Prerpints.org logo
Preprint
Article

Synthesis, Crystal Structure and Spin-Orbit Coupling Analysis for Mono-Scorpionate Eu(III) Complexes

Altmetrics

Downloads

129

Views

45

Comments

0

A peer-reviewed article of this preprint also exists.

supplementary.zipΒ (2.63MB )

Submitted:

25 August 2023

Posted:

25 August 2023

You are already at the latest version

Alerts
Abstract
Complexes of triply positive europium ion with organic ligands are popular objects for studying photophysical properties. This is related not only to the bright red emission of this 4f element, but also to some spectroscopic peculiarities of its luminescence: the first excited spin-orbit level (7F1) lies only about 300 cmβˆ’1 above the ground state (7F0), so that at room temperature its population is around 25–30%. However, such electronic structure of Eu(III) provides its paramagnetism under ordinary conditions. This fact is often ignored by researchers, which is shortsighted from the materials science point of view. A comprehensive and systematic study of the magnetic behavior for the Eu(III) molecular coordination compounds is a challenging task for the development of new polyfunctional materials. The present work presents synthesis, single crystal XRD analysis results, and a magnetic study for the firstly prepared europium(III) complexes with two neutral scorpionate ligands: trispyrazolylmethane (HCPz3) and its methylated analog, tris(3,5-dimethyl-1-pyrazolyl)methane (HC(PzMe2)3). The values of the spin-orbit coupling parameter obtained for Eu-trication by a theoretical approximation of the experimental magnetic susceptibility data are compared with those known for the scarce amount of the magnetically studied molecular compounds.
Keywords:Β 
Subject:Β Chemistry and Materials ScienceΒ  - Β  Inorganic and Nuclear Chemistry

1. Introduction

The design of molecular materials with newly developed functionalities holds potential for technological advances. Switchable by different stimuli molecules are appealing model compounds due to their potential for electronic handling. This requires implementation of diverse physical properties within monophasic materials designable at the molecular level. As the result, such materials should become the tool for optical, magnetic, electronic, and multifunctional devices linking high performance with extreme miniaturization. For these purposes, realizing how the fundamental properties of molecular coordination compounds arise and how they can be controlled is very important for the creation of new functional molecular materials.
The unique electronic and physical properties of rare earth ions have been utilized for a variety of applications, including magnetic and luminescent materials. The focus in this direction is on luminescent single-molecule magnets (SMMs) searching for rational synthetic approaches resulting in strong magnetic anisotropy and enhanced photoluminescence since the latter can be used to probe the electronic structure of lanthanide based SMMs deposited on a surface [1,2].
The most common are the lanthanide (Ln) compounds in which the metal ion is in the trivalent state, and the redox activity in lanthanide complexes is usually limited to the ligand. However, lanthanide-based redox activity is also possible. Among the divalent lanthanides, europium possesses the most reachable divalent oxidation state, Eu2+, because of its half-filled 4f7 electronic configuration and, therefore, a high stabilization from exchange energy [3,4]. For this reason in a vast majority of the magnetically studied Eu3+ molecular complexes, their magnetic susceptibility experiences an increase at near liquid helium temperatures since the presence a tiny amount of Eu2+ impurity [5,6].
To date, there is abundant information on the photophysical properties of Eu3+ molecular complexes, which are quite well studied spectroscopically. However, due to the non-magnetic ground term 7F (S = L = 3) of the ion, researchers often leave the magnetic properties of europium luminescent compounds unattended. Although due to the thermal population of the excited states, Eu3+ becomes noticeably paramagnetic already at 100 K, reaching a value of effective magnetic moment of ~ 3.2 Β΅B at room temperature. Given the low redox potential of the Eu2+/Eu3+ pair [7], which in combination with non-innocent organic ligands can lead to interesting both photo- and magnetically switchable materials, including SMMs [8,9].
Tuning the electronic properties of a compound is the most common challenge for materials scientists. This can be achieved by varying the ligand environment of the central atom, namely the geometry of the polyhedron and the ligand field strength. The latter is mainly determined by the nature of the donor atoms, whereas the former depends not only on the geometry of the ligand but also on the predictable way in which it is coordinated. Organic tripod molecules having donor atoms on each of the three legs are the most prospective for the chemical construction of various complexes with a prescribed geometry. Moreover, the latter can be easily adjusted by methods of synthetic organic chemistry.
Previously, we have obtained the monoradical, [LnRad(NO3)3] (Ln3+ = Gd, Tb, Dy, Tm [10], and biradical [Ln(Rad)2(OTf)3] (Ln3+ = Eu and Dy) [11] complexes, where Rad is a tripodal nitroxyl radical (Scheme 1(a)), 4,4-dimethyl-2,2-bis(pyridin-2-yl)-1,3-oxazolidine-3-oxyl. We were somewhat surprised by molar magnetic susceptibility values of 1.78 and 0.348 emuK/mol at 300 and 2 K respectively for the biradical complex, comparing them with those of [Eu(radical)2(anion)3] compounds [12,13,14,15,16,17,18]. In this series, they were varied from 1.93 to 3.09 emu K/mol at room temperature, and from 0.035 to 0.42 emuK/mol at low temperature. Analyzing the literature data for known Eu3+ biradical complexes, we have noticed that the rough estimates of magnetic parameters values for such systems resulted in a large scatter in values of Ξ», spin-orbit coupling (SOC) parameter.
It should also be pointed out that there is no reasonable explanation for the underestimated magnitudes of the molar magnetic susceptibility of [Eu(radical)(anion)3] complexes at low temperature (0.192Γ·0.252 instead of 0.375 emuK/mol) [19,20,21] when a singlet state is operative for Eu3+. These two facts are most likely due to the lack of models to account for the strong spin-orbit coupling (SOC) for the Eu3+ complexes with paramagnetic ligands. In addition, preliminary magnetic studies of the isomorphic analogue [EuRad(NO3)3] did not clarify the situation with the underestimation of the low-temperature Ο‡MT value for the monoradical europium complexes mentioned above, since the value of Ο‡MT for [EuRad(NO3)3] at 2 K lies in the same range. Considering that the Ln–Rad antiferromagnetic coupling found for the [GdRad(NO3)3] complex is –23 cmβˆ’1 [10], an ambient temperature Ο‡MT value for [EuRad(NO3)3] can be estimated as a sum of the contributions of the uncorrelated radical (0.375 emuK/mol) and [EuLdia(NO3)3]. The latter is a model complex of a diamagnetic tripodal ligand possessing a coordination polyhedron geometry close to that of the radical complex. Such a strategy of diamagnetic substitution for obtaining information on the crystal field (CF) effects in paramagnetic Ln ions has been applied earlier [15,22,23]. This experimental approach aims to reveal the nature of the coupling between the radical and the lanthanide subtracting the CF splitting. This method was applied for two homologous series of complexes: [LnNNtrz2(NO3)3] and [Ln(Nitrone)2(NO3)3] [15]; [Ln(HBPz3)2SQ] and [Ln(HBPz3)2Trp] [22,23]. Where NNtrz is 2-(4β€²,5β€²-dimethyl-1β€²,2β€²,3β€²-triazolyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy-3-oxide, and SQ is 3,5-di-tert-butylsemiquinonato respectively, while the diamagnetic homologue ligands, Nitrone and Trp are 3-N-tert-butylnitrone-4,5-dimethyltriazole and tropolonate correspondingly.
To determine the reference values of the magnetic susceptibility of Eu(III) complexes with diamagnetic tripodal ligands with similar geometry of the coordination polyhedron, we synthesized and magnetically studied three Eu3+ complexes comprising diamagnetic tripodal ligand depicted in Scheme 1.

2. Short Theoretical Background

The trivalent europium ion (Eu3+) shows an intense red photoluminescence upon irradiation with ultra violet radiation [24]. This luminescence is observed not only for Eu3+ ions doped into crystalline host matrices or glasses, but also for europium(III) complexes with organic ligands [25]. These ligands can act as an antenna to absorb the excitation light and to transfer the excitation energy to the higher energy levels of the Eu3+ ion, from which the emitting excited levels can be populated [2]. Not only its red luminescence, but also the narrow transitions in luminescence spectra are typical features of the Eu3+ ion [26], and these spectroscopic properties have been known from the earliest history of the chemical element europium [27]. Many Eu3+ compounds show an intense photoluminescence, due to the 5D0 β†’ 7FJ transitions (J = 0–6) from the 5D0 excited state to the J levels of the ground term 7F. The fine structure and the relative intensities of the transitions in luminescence spectra of Eu3+ can be used to probe the local surroundings of the europium. The spectroscopic experimental data provide information on the point group symmetry of the Eu3+ site and as well as on the polyhedron geometry [26], which it is especially useful for solution study. Other techniques (optical, magnetic or magneto-optical) can also be used for determination of the position and assignment of the CF energy levels inside the 4f shell: two-photon absorption, Zeeman spectroscopy and magnetic circular dichroism [24].
In the first approximation, a lanthanide ion in a molecular coordination compound behaves as a free-ion. The paramagnetic behavior of the tripositive Ln3+ ions is due to the presence of unpaired 4f-unpaired electrons. Since these electrons are shielded by the outer electronic closed shell, the spin-orbit interaction is believed to play a decisive role in their magnetic properties. Therefore, depending on the sign of the spin-orbit interaction, their total magnetic moments J defined as J = L Β± S, where L means the angular momentum and S – the spin momentum. It follows that the magnetic moment of the complex should indicate whether these 4f-electrons are involved in bond formation or not. For a majority of the Ln3+ ions, the 2s+lLJ free-ion ground state (GS) is well isolated in energy from the first excited state. Therefore, only the GS is thermally populated in the temperature range of 0Γ·300 K. In the free-ion approximation the molar magnetic susceptibility for a mononuclear species is given by [28]
Ο‡ J = N g J 2 Ξ² 2 J J + 1 3 k T + 2 N Ξ² 2 g J βˆ’ 1 3 Ξ»
where Ξ» is the spin-orbit coupling parameter and gJ is equal to
g J = 3 2 + S S + 1 –   L L + 1 2 J J + 1
and L is the orbital quantum momentum. For J = 0 there is obviously no first-order Zeeman splitting. However, application of a magnetic field can result in second-order splitting and appearance of a net magnetic moment. The last part in (1) is a temperature independent contribution arising from the coupling between the ground and excited states through the Zeeman perturbation. For Ln molecular compounds the Ο‡MT versus T curve often differs slightly from what is predicted by (1). This deviation occurs for two reasons: the crystal field, which partially removes the 2J + 1 degeneracy of the GS in zero field, and the thermal population of Ln3+ excited states. The latter is most pronounced for tripositive samarium and europium, which possess excited states located close in energy to the ground one. In the case of europium, its 7F ground term is split by the spin-orbit coupling into seven multiplets (7F0, 7F1, 7F2, 7F3, 7F4, 7F5, 7F6), whose energies are E(J) = Ξ»J(J + 1)/2, where the energy of the 7F0 ground state is taken as the origin. Since Ξ» is small enough for the first excited states to be thermally populated, the magnetic susceptibility may be written as
Ο‡ M = βˆ‘ J = 0 6 J + 1 Ο‡ J e βˆ’ Ξ» J J + 1 2 k T βˆ‘ J = 0 6 2 J + 1 Ο‡ J e βˆ’ Ξ» J J + 1 2 k T    [ 28 ]
where Ο‡J is given by equation (1). In the case of Eu3+, all of the gJ are equal to 3/2, except g0, which is equal to 2 + L(=2 + S) = 5, i.e. (Ο‡MT)Eu can be expanded as [29]:
N Ξ² 2 3 k x [ 24 + 27 2 x βˆ’ 3 2 e βˆ’ x + 135 x βˆ’ 9 2 e βˆ’ 3 x + 189 x βˆ’ 7 2 e βˆ’ 6 x + 405 x βˆ’ 9 2 e βˆ’ 10 x + 1485 2 x βˆ’ 11 2 e βˆ’ 15 x + 2457 2 x βˆ’ 13 2 e βˆ’ 21 x ] [ 1 + 3 e βˆ’ x + 5 e βˆ’ 3 x + 7 e βˆ’ 6 x + 9 e βˆ’ 10 x + 11 e βˆ’ 15 x + 13 e βˆ’ 21 x ]
where x = Ξ»/kT.
At moderate temperatures, owing to the value of Ξ» ~ 350 cmβˆ’1 [28], only the first three lower states (7F0, 7F1, 7F2) having the energies 0, Ξ», and 3Ξ» can be considerably populated; since the 7F0 ground state is formally nonmagnetic, the lower limit of Ο‡T is zero. However, the low-temperature limit of the magnetic susceptibility, Ο‡LT, is nonzero due to the temperature-independent contribution arising from the coupling between the ground and excited states. According to equation (4) which acquires a very simple form in the T = 0 limit, the Ο‡LT value is directly related to Ξ» as:
Ο‡LT = 8NΞ²2/Ξ» = (2.085 Γ— l0βˆ’3)/Ξ» (Ξ» in cmβˆ’1)
Although the aforementioned description has proved to capture the key qualitative features of the magnetic susceptibility of Eu3+-based compounds, its performance turns out to be not as good when it comes to precise determination of Ξ» and quantitative comparison with spectroscopic results. The problem stems from the crystal-field splitting of the excited J β‰  0 multiplets that has not been taken into account by the equation (4) [29,30,31] Given that the 7F1 multiplet is the closest one in energy to the ground level, its splitting into three Stark sublevels plays the most important role. For example, when we consider the low-T magnetic susceptibility and take into account the splitting of the first excited multiplet, the equation (6) turns into:
Ο‡LT = (8NΞ²2/3)(1/E1+1/E2+1/E3)
where E1, E2, E3 are the energies of the 7F1-multiplet Stark sublevels. Apparently, when the multiplet splitting is negligible, the eq. (6) and (7) are equivalent, as 1/E1= 1/E2= 1/E3= 1/Ξ». But, in the opposite case of strong splitting, the average (1/E1+1/E2+1/E3)/3 becomes significantly larger than 1/Ξ», resulting in the magnetic susceptibility in the low-temperature plateau region to be enhanced in comparison with the values predicted by the eq. (4) [31].

3. Results and Discussion

3.1. Synthetic Aspects

As can be seen in Scheme 1, the paramagnetic tripod, Rad, has a close to its diamagnetic relatives organization of the organic molecule. Formally, it can be referred to methane derivatives, like the other two tripodal ligands, since for all three molecules the bridgehead atom is a carbon. In addition, despite the difference in the donor atoms on the legs of the paramagnetic tripod (oxygen atom from the nitroxyl group instead of the nitrogen of the pyrazole), it also forms three six-membered chelate cycles when coordinated.
Upon coordination of the neutral tripods, (tris(pyrazol-1-yl)methanes), anionic ligands enter the coordination sphere of the formed complex to compensate for the charge of the central atom [32,33], in contrast to their negatively charged congeners, tris(pyrazol-1-yl)borates (TPB), for which the neutral complexes LnIII(TPB)3 [34,35,36,37,38] and LnII(TPB)2 [39,40,41] can be assembled.
An interaction of Eu(NO3)3Ξ‡5H2O with a tripodal ligand in a 1:1 ratio in acetonitrile solution leads to a formation of mono-aqua complex [Eu(HCPz3)(NO3)3H2O]Ξ‡2MeCN (1), when reacting with unsubstituted trispyrazolylmethane tripod, (HCPz3); and a water free nitrate compound, [Eu(HC(PzMe2)3)(NO3)3]Ξ‡MeCN (2), upon coordination of the methylated congener of HCPz3 – tris(3,5-dimethyl-1-pyrazolyl)methane. The absence of aqua–ligand in 2 is most likely due to the steric hindrance of the PzMe2–tripod. It is worth noting that for the chloride analogue, [Ln(HC(PzMe2)3)Cl3]Ξ‡2MeCN, no water molecule were also found enter the coordination sphere upon the reaction in acetonitrile under obvious conditions [42], whereas the interaction of hydrated salt, EuCl3Ξ‡6H2O, with HCPz3 in tetrahydrofuran results in a six-aqua complex – [EuHC(Pz)3(H2O)6]Cl3 [25].
The seven-coordinate mono-tripod complexes, [Ln(HC(PzMe2)3)(OTf)3(thf)], where Ln = Y, Ho, Dy were formed in a dry and inert tetrahydrofuran media [32]. However, in open air, a reaction of one equivalent of europium(III) triflate with one equivalent of HCPz3 in acetonitrile solution results in a dimerized entity [Eu(HCPz3)H2O(CF3SO3)3]2 (3), in which the central atoms are also seven-coordinate. The crystals of 3 contain the solvate molecules of acetonitrile and diethyl ether, which escape easily during storage of the compound. Interestingly, using unsubstituted anionic tripod, hydro-tris(pyrazolyl)borate (HBPz3), in an inert and dry atmosphere in , the dimeric compounds [Ln(HBPz3)2(CF3SO3)]2 were also obtained for Ln = Y, Eu in which the two triflates are bridged. In contrast, the molecular structures of Gd and Yb are monomeric THF-adducts [Ln(HBPz3)2(CF3SO3)thf] [43].

3.2. Description of the Crystal Structures 1–3

A summary of the crystallographic data and the structure refinement is given in Table S1 (Supplementary information, SI). As established by X-ray diffraction experiment, the mononuclear compounds crystallize in the following space groups P–1, I2/c, and P21/n for 1, 1a and 2 respectively, whereas a binuclear specie 3 – in P21/c. In all compounds, each metal central atom is capped with one neutral tripodal ligand. Among the structurally studied heteroleptic complexes, only 1a does not have solvate molecules. 1 differs from 1a by presence of solvate acetonitrile molecules in its crystal structure. In both compounds, a europium center has a coordination number of ten consisting of three nitrogens of trispyrazolylmethane, six oxygens of bidentate nitrate anions and one aqua–oxygen, Figure 1.
The Eu-N distances of 1 are in the range of 2.5810(12) to 2.5932(12) Γ…, which are somewhat larger than those for nitrates (2.4846(10)-2.5687(11) Γ…), the distance of the Eu-Oaqua bond of 2.4191(11) Γ… being a shortest one, Table 1. The same tendency is observed and for other compounds. However, the most compact is a coordination environment of 2, which contains one solvated acetonitrile molecule, Figure 2a. According to analysis of the 10-coordinate polyhedrons using SHAPE program [44], a geometry of the lanthanide site in 1 and 1a can be best described as a sphenocorona (C2v), while for the 9-coordinate environment of 2, a spherical tricapped trigonal prism (D3h) is more acceptable (Table S2, SI).
Among all studied complexes 1-3, the most intriguing is a molecular structure of 3 in which there are two independent Eu3+ sites with coordination number of eight (Figure S1), which is composed of three trispyrazolylmethane nitrogens, two ΞΌ2-oxygens of bidentate triflate anions, two oxygens from monodentate triflate ligand, and one aqua–oxygen. A duplication of the corresponding independent parts via an inversion center gives two different dimeric molecules. One of them is shown in Figure 2b. In addition to the two bidentate triflate ligands, each binuclear entity is supported by two water–triflate hydrogen bonds, which are in a plane perpendicular to that in which the bridging anions are located, thus forming a Chinese lantern structure. The stereochemical analysis results indicate that the geometry of the coordination environment for both metal sites corresponds to a square antiprism (D4d) to a good approximation (Figure S2, Table S2, SI). Nevertheless, despite the similar polyhedron geometry, the two Eu sites differ quite significantly in the bond lengths of europium atoms to donors being on average shorter for Eu1 (Table 1).
Crystal packing analysis shows that the shortest Eu …. Eu distances are in the range of 6.073 Γ· 8.931 Γ… (Table 1). These distances have an intermolecular character only for 2, for which no hydrogen bonds were detected, while 3 is a binuclear specie and the compounds 1 and 1a are dimerized by double hydrogen bounding (Figure S3, SI). The distances of the shortest intermolecular contacts between a tripod and anionic ligand, CHL…Oanion, are 3.281, 3.245, 3.334 and 3.325 Γ… for 1, 1a, 2 and 3 respectively.

3.3. Magnetic Behavior of The Complexes

The experimental dc magnetic susceptibility for the complexes 1–3 measured in the temperature range from 1.77 to 300 K at the applied magnetic field H = 1 kOe are shown in Figure 3 as plots of Ο‡MT vs. T, where Ο‡M is the molar magnetic susceptibility corrected for the diamagnetic core contribution. As expected, due to the thermal depopulation of the excited levels with non-zero J values, Ο‡MT gradually decreases with cooling and tends to a value very close to zero as the temperature approaches absolute zero. The Ο‡MT values at low and room temperature for all complexes are summarized in Table 2. Below β‰ˆ 100 K, Ο‡MT varies almost linearly with T (Figure 3), implying the magnetic susceptibility Ο‡M to be nearly temperature independent at low T. Indeed, the Ο‡M(T) dependencies (presented in Figure S4, SI) exhibit a smooth growth upon cooling, tending to saturate and form a plateau below ~100 K. A small increase of Ο‡M at very low temperatures is due to the inevitable presence of Eu2+ impurities (at a level of 0.01-0.017 at.%) or other rare-earth impurity ions possessing paramagnetic ground state. Subtraction of this impurity contribution recovers the intrinsic temperature-independent magnetic susceptibility of Eu3+ ions.
The temperature dependences of Ο‡MT in Figure 3 can be analyzed using the van Vleck approximation (3), (4) and assuming a simplified electronic structure of Eu3+ ion composed of seven multiplets with energies E(J) = Ξ»J(J + 1)/2 [29]. The least squares fitting using equation (4) with Ξ» as the only adjustable parameter (dashed blue lines in Figure 3) results in the Ξ» values of β‰ˆ 383–406 cmβˆ’1 for 1-3 (Table 2) – values typical for Eu3+ compounds. A common feature of all these fits that is worth mentioning is that the fits underestimate the Ο‡MT values in the low-temperature region where Ο‡M exhibits a plateau. As we have discussed in Sec.2, this feature is quite expected because the equation (4) does not take into account zero-field splitting of the excited multiplets with J β‰  0. The latter inevitably reduces the energy difference between the ground-state J = 0 level and the lowest in energy sublevel of the J = 1 multiplet, E1 [29,30,31]. In the case of strong zero-field splitting, E1 may be significantly smaller than Ξ», thereby providing the low-T magnetic susceptibility to be much larger than Ο‡LT = 8NΞ²2/Ξ» predicted by the equation (4) [31].
In the entire available temperature range the field dependences of the magnetization M(H) demonstrate an almost perfect linear behavior (Figure 4). The magnitude of the magnetization is however 2-3 orders of magnitude lower than for other rare-earth ions with a J β‰  0 ground state; even at the lowest temperature T = 1.77 K the magnetization at H = 10 kOe amounts only to β‰ˆ 0.01 ΞΌB per Eu3+ ion. These features are common to many other europium(III) complexes with diamagnetic ligands accumulated in Table 2.

3.4. Spin-orbit Coupling Parameter Analysis

For all compounds, the values of R, the factors of agreement of the theoretical curves with the experimental ones, given in Table 2, indicate the applicability of the chosen qualitative model. However, for nitrate-containing complexes 1 and 2 this agreement is better compared to 3. This is most likely due to the significant difference in the splitting of Eu3+ excited levels (especially of 7F1 state) under the action of the crystal field.
Indeed, despite approximately the same set of donor atoms: nitrogens from a tripodal ligand and oxygens from the anion ligands, the latter, in compound 3, have a pronounced electron withdrawing character. Whereas nitrate ligands do not possess such a property, which is confirmed by the difference in the lengths of Eu-O bonds (Table 1). In addition, despite the presence of two different europium sites in 3, the symmetry of their local environment (D4d) is higher than that of the other two: C2v for 1 and D3h for 2 (Table S2, SI). Based on the above, it is not surprising that simulating the experimental curve using just one variable, Ξ», for 3 leads to a lower-quality result compared to 1 and 2. In addition, for a more accurate description of the high-temperature interval, it may be necessary to neglect the Eu-Eu exchange interaction, for which it may be necessary to take into account the interaction between Eu ions, by introducing into the set of variables also the coupling constant jEu-Eu. However, without an additional experimental data such as the luminescence spectra, the use of five independent variables would lead to overparametrization.
According to the agreement coefficients R, the modelling quality achieved is sufficient to conclude that the spin-orbit coupling parameters Ξ» in 1 and 2 are different (by ~10 cmβˆ’1). Indeed, despite the same type of tripod and anionic ligands, the coordination environment of the Eu site is significantly different for 1 and 2, due to the presence of one water molecule in the former. Therefore, 1 has a lower symmetry of the coordination polyhedron compared to 2, which leads to a smaller splitting of the excited levels in the crystal field. This fact is consistent with the higher value of Ξ»: 406 for 1 vs. 396 cmβˆ’1 for 2.

4. Experimental Section

4.1. Materials and Physical Measurements

Ln(CF3SO)3 salts (Thermo Fisher GmbH, Kandel, Germany) were purchased from Alfa Aesar. Eu(NO3)3Β·6H2O was prepared upon dissolution of the corresponding Eu2O3 in diluted HNO3 at 50Β°C followed by crystallization during slow evaporation of reaction mixture. Solvents of the reagent grade (EKOS-1, Moscow, Russia) were distilled prior to use. The complexes were synthesized under aerobic conditions. Elemental (C, H, N, S) analyses were carried out by standard methods with a Euro-Vector 3000 analyzer (Eurovector, Redavalle, Italy).
Magnetic measurements were performed using a Quantum Design MPMS-XL SQUID magnetometer in the temperature range of 1.77–300 K at magnetic fields up to 10 kOe. In order to determine the paramagnetic component of the molar magnetic susceptibility, Ο‡MT(T), the temperature-independent diamagnetic contribution, Ο‡d, and a possible magnetization of ferromagnetic micro-impurities, Ο‡FM(T), were evaluated and subtracted from the measured values of the total molar susceptibility, Ο‡ = M/H. The diamagnetic intrinsic contributions of the compounds Ο‡d were estimated using the Pascal’s Constants [58]. Fourier transform infrared (FTIR) spectra were measured in KBr pellets with a Perkin–Elmer System 2000 FTIR spectrometer (Perkin Elmer, Waltham, MA, USA) in the 4000–400 cmβˆ’1 range.

4.2. Single-crystal XRD experiment and data refinment details

Single-crystal XRD data for crystals of the compounds were collected at 150 K with a Bruker D8 Venture diffractometer (0.5Β° Ο‰- and Ο†-scans, fixed-Ο‡ three circle goniometer, CMOS PHOTON III detector, IΞΌS 3.0 micro-focus source, focusing Montel mirrors, Ξ» = 0.71073 Γ… MoKΞ± radiation, N2-flow thermostat). Data reduction was performed routinely via APEX 3 suite [59]. The crystal structures were solved using the ShelXT [60] and were refined using ShelXL [61] programs assisted by Olex2 GUI [62]. Atomic displacements for non-hydrogen atoms were refined in harmonic anisotropic approximation, with the exception for partially occupied diethyl ether molecule in 3. Hydrogen atoms were located geometrically with the exception for those in water molecules in 1 and 1a, which were refined freely with the restraints on O–H bond. All hydrogens were placed in geometrically idealized positions, and refined in a riding model. Crystals of compound 3 tend to form twins; as a result, the quality of the structure is lower than in the others. The structures of were deposited to the Cambridge Crystallographic Data Centre (CCDC) as a supplementary publication, No. 2285187-2285190.

4.3. Synthesis of the Complexes

[Eu(HCPz3)(NO3)3H2O]Ξ‡2MeCN (1) A solution of trispyrazolylmethane (64.5 mg, 0.3 mmol) in acetonitrile (0.5 mL) was added dropwise to a stirred warm solution of Eu(NO3)3(H2O)5 (128 mg, 0.3 mmol) in acetonitrile (0.5 mL). The next day, the crystalline colorless precipitate was filtered, washed with a small amount of acetonitrile, and Et2O and air-dried. Yield: 158 mg (81%) (652.32 g/mol). Storage of the compound resulted in unsolvated 1. Anal. calcd. (%) for C10H12EuN9O10: C, 21.02; H, 2.12; N, 22.07. Found: C, 21.1; H, 2.0; N, 22.1. IR (KBr): Ξ½ (cmβˆ’1) 3423 (m), 3115 (m), 3111 (m), 2505 m, 2427 (sh), 1507 (s), 1384 (s), 1317 (s), 1285 (s), 1230 (m),1148 (s), 1186 (s), 1148 (s), 1136 (s), 1119 (m), 1042 (m), 1028 (m), 1009 (m), 981 (m), 963 (m), 904 (m), 876 (m), 730 (s), 723 (s), 672 (s), 664 (s), 651 (m).
[Eu(HCPz3)(NO3)3H2O] (1a). The mother liquor combined with flushing liquids (the both left after synthesis of 1 were evaporated to dryness. The white powder formed (30 mg) was dissolved in hot dry acetonitrile (2 mL). After filtration, the filtrate was left in a refrigerator at a temperature of 4 C during one week. The colorless crystals were filtered, rinsed with a small amount of cold acetonitrile and air-dried. Yield: 17 mg (570.22 g/mol); Anal. calcd. (%) for C10H12EuN9O10: C, 21.02; H, 2.12; N, 22.07. Found: C, 21.2; H, 2.1; N, 22.0. I. IR (KBr) is similar to that of 1.
[Eu(HC(PzMe2)3)(NO3)3]Ξ‡MeCN (2) To a stirred and hot solution of the metal salt (84 mg (0.2 mmol) of Eu(NO3)3(H2O)5) in acetonitrile (1.5 mL), solid tris(3,5-dimethyl-1-pyrazolyl)methane (60 mg, 0.2 mmol) was gradually added under heating. The solution was filtered and kept at room temperature overnight, and then the resulting colorless crystalline solid was sucked off, washed twice with cold acetonitrile and air-dried. Yield: 112 mg (84 %) (677.41 g/mol). Storage of the compound resulted in unsolvated 3. Anal. calcd. (%) for C16H22EuN9O9: C, 30.14; H, 3.48; N, 19.65. Found C, 30.2; H, 3.3; N, 19.65. IR (KBr) Ξ½ (cmβˆ’1) : 487 (m); 636 (w); 707 (s); 746 (s); 802 (m); 811 (s); 822 (w); 836 (m); 859 (s); 864 (s); 906 (s); 983 (m); 1024 (s); 1042 (s); 1109 (m); 1153 (w); 1169 (w); 1276 (s); 1304 (s); 1417 (m); 1515 (s); 1530 (m); 1570 (s); 1732 (w); 1771 (w); 1977 (w); 2043 (w); 2268 (m); 2292 (w); 2533 (w).
[Eu(HCPz3)H2O(CF3SO3)3]2·2MeCN·0.73Et2O (3). A solution of trispyrazolylmethane (54 mg, 0.25 mmol) in acetonitrile (1 mL) was added dropwise to a stirred solution of Eu(CF3SO3)3·(150 mg, 0.25 mmol) in acetonitrile (2 mL). The reaction mixture was halved by heating (65 C) and slowly cooled to room temperature, and then left undisturbed overnight in a closed vessel with a few drops of Et2O. The crystalline colorless solid was filtered, washed with a small amount of acetonitrile, and Et2O and air-dried. Yield: 209 mg (45%) C32.9H37.24Eu2F18N14O20.73S6 (1798.66 g/mol). Storage of the compound resulted in unsolvated 4. Anal. calcd. (%) for C26H24Eu2F18S6N12O20 (1662.8 g/mol): Anal. calcd. (%): C, 18.78, H, 1.45, N, 10.11; S, 11.7; found: C, 18.6, H, 1.6, N, 10.0; S, 11.5. IR (KBr) ν (cm-1) : 3140 (w); 3130 (w); 1578 (m); 1549 (m); 1527 (m); 1409 (m); 1292 (s); 1200 (s); 1166 (s); 1110 (m); 1094 (m); 1029 (m); 960 (m); 920 (m); 889 (m); 857 (m); 824 (m); 810 (m); 755 (s); 722 (m); 638 (s); 597 (m); 574 (m); 517 (m); 410 (w); 389 (w); 351 (w).

5. Conclusions and perspectives

In the absence of analytical models accounting for strong spin-orbit coupling for Eu3+ complexes with paramagnetic ligands, alternative approaches are needed to determine the nature and magnitude of the exchange coupling between paramagnetic centers in such complicated systems. The proposed earlier solution, based on subtraction from the experimental dependence of the magnetic susceptibility, Ο‡M(T), for a series of lanthanide complexes with radicals [15,23] the same dependence of the model compound of the corresponding Ln with a diamagnetic ligand possessing a similar coordination polyhedron geometry turned out to be particularly effective for [Ln(HBPz3)2SQ] [23].
In the present study, we were able to find a model system, [Ln(HC(PzMe2)3)(NO3)3], for monoradical complexes [LnRad(NO3)3] since both types of compounds have the same type of coordination polyhedron and very close Ln – donor atoms distances. It is quite possible that the neutral ligand HC(PzMe2)3 can also be used for the synthesis of bis-tripodal complexes [Ln(HC(PzMe2)3)2](anion)3 as model systems for biradical compounds with sterically hindered paramagnetic tripods [Ln(Rad)Me2](anion)3, for which the corresponding ligands are under preparation. As surprising as it may be, the homoleptic Ln3+ complexes involving two balky diamagnetic tripods of type HC(PzMe2)3 in their composition are still unknown. Consequently, developing methods to synthesize them is a particular challenge.

Author Contributions

Conceptualization, K.E.V.; funding acquisition, K.E.V.; investigation, K.E.V., V.S.M. and E.V.P.; supervision K.E.V.; visualization, K.E.V. and V.S.M.; writingβ€”original draft, K.E.V., V.S.M. and E.V.P.; writingβ€”review and editing, K.E.V., V.S.M. and E.V.P. All authors have read and agreed to the published version of the manuscript.

Supplementary Materials

The following supporting information can be downloaded at the website of this paper posted on Preprints.org, Table S1: Crystal data and structure refinement for the compounds; Figure S1: The asymmetric unit in the crystal structure of [Eu(HCPz3)H2O(CF3SO3)3]2 (3); Figure S2: Square antiprism coordination environment - of Eu3+ sites in [Eu(HCPz3)H2O(CF3SO3)3]2 (3) for: (a) around Eu1 central atom, (b) around Eu2 central atom; Table S2: Geometry analysis of the complexes by SHAPE software; Figure S3: Dimerized species in 1 (left) and 1a (right); Figure S4: The temperature-dependent molar magnetic susceptibility for 1–3 measured at a field of 1 kOe in the 1.8–300 K temperature range.

Author Contributions

Conceptualization, K.E.V. and A.N.L.; methodology, K.E.V.; software, T.S.S.; formal analysis, T.S.S.; investigation, K.E.V. and A.N.L.; resources, X.X.; data curation, T.S.S.; writingβ€”original draft preparation, K.E.V.; writingβ€”review and editing, K.E.V. and A.N.L.; visualization, K.E.V. and A.N.L.; supervision, K.E.V.; funding acquisition, K.E.V. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Russian Science Foundation, Grant No. 23-23-00437, and partially supported by the Ministry of Science and Higher Education of the Russian Federation (crystal structure determination for the complexes, 121031700313-8).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

CCDC 2285187-2285190 for 1–4 contain the supplementary crystallographic data for this paper, and can be obtained free of charge from The Cambridge Crystallographic Data Centre via https://www.ccdc.cam.ac.uk/structures/ (accessed on 31 July 2023).

Acknowledgments

In this section, you can acknowledge any support given which is not covered by the author contribution or funding sections.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Yi, X.; Bernot, K.; Pointillart, F.; Poneti, G.; Calvez, G.; Daiguebonne, C.; Guillou, O.; Sessoli, R. A Luminescent and Sublimable DyIII-Based Single-Molecule Magnet. Chem. – A Eur. J. 2012, 18, 11379–11387. [Google Scholar] [CrossRef]
  2. Marin, R.; Brunet, G.; Murugesu, M. Shining New Light on Multifunctional Lanthanide Single-Molecule Magnets. Angew. Chemie Int. Ed. 2021, 60, 1728–1746. [Google Scholar] [CrossRef] [PubMed]
  3. Suta, M.; Wickleder, C. Synthesis, Spectroscopic Properties and Applications of Divalent Lanthanides Apart from Eu2+. J. Lumin. 2019, 210, 210–238. [Google Scholar] [CrossRef]
  4. Morss, L.R.B.T.-H. on the P. and C. of R.E. Chapter 122 Comparative Thermochemical and Oxidation-Reduction Properties of Lanthanides and Actinides. In Lanthanides/Actinides: Chemistry; Elsevier, 1994; Vol. 18, pp. 239–291 ISBN 0168-1273.
  5. Rodrigues, L.C.V.; HΓΆlsΓ€, J.; Brito, H.F.; MaryΕ‘ko, M.; Matos, J.R.; Paturi, P.; Rodrigues, R.V.; Lastusaari, M. Magneto-Optical Studies of Valence Instability in Europium and Terbium Phosphors. J. Lumin. 2016, 170, 701–706. [Google Scholar] [CrossRef]
  6. Chen, J.; Carpenter, S.H.; Fetrow, T.V.; Mengell, J.; Kirk, M.L.; Tondreau, A.M. Magnetism Studies of Bis(Acyl)Phosphide-Supported Eu3+ and Eu2+ Complexes. Inorg. Chem. 2022, 61, 18466–18475. [Google Scholar] [CrossRef]
  7. Evans, W.J. Perspectives in Reductive Lanthanide Chemistry. Coord. Chem. Rev. 2000, 206–207, 263–283. [Google Scholar] [CrossRef]
  8. Dolai, M.; Ali, M.; RajnΓ‘k, C.; TitiΕ‘, J.; Boča, R. Slow Magnetic Relaxation in Cu(II)–Eu(III) and Cu(II)–La(III) Complexes. New J. Chem. 2019, 43, 12698–12701. [Google Scholar] [CrossRef]
  9. Wang, J.; Ruan, Z.-Y.; Li, Q.-W.; Chen, Y.-C.; Huang, G.-Z.; Liu, J.-L.; Reta, D.; Chilton, N.F.; Wang, Z.-X.; Tong, M.-L. Slow Magnetic Relaxation in a {EuCu5} Metallacrown. Dalt. Trans. 2019, 48, 1686–1692. [Google Scholar] [CrossRef]
  10. Perfetti, M.; Caneschi, A.; Sukhikh, T.S.; Vostrikova, K.E. Lanthanide Complexes with a Tripodal Nitroxyl Radical Showing Strong Magnetic Coupling. Inorg. Chem. 2020, 59, 16591–16598. [Google Scholar] [CrossRef]
  11. Rey, P.; Caneschi, A.; Sukhikh, T.S.; Vostrikova, K.E. Tripodal Oxazolidine-N-Oxyl Diradical Complexes of Dy3+ and Eu3+. Inorganics 2021, 9, 91. [Google Scholar] [CrossRef]
  12. Tretyakov, E.V.; Fokin, S. V; Zueva, E.M.; Tkacheva, A.O.; Romanenko, G. V; Bogomyakov, A.S.; Larionov, S. V; Popov, S.A.; Ovcharenko, V.I. Complexes of Lanthanides with Spin-Labeled Pyrazolylquinoline. Russ. Chem. Bull. 2014, 63, 1459–1464. [Google Scholar] [CrossRef]
  13. Wang, X.; Li, Y.; Hu, P.; Wang, J.; Li, L. Slow Magnetic Relaxation and Field-Induced Metamagnetism in Nitronyl Nitroxide-Dy(III) Magnetic Chains. Dalt. Trans. 2015, 44, 4560–4567. [Google Scholar] [CrossRef]
  14. Wang, Y.; Fan, Z.; Yin, X.; Wang, S.; Yang, S.; Zhang, J.; Geng, L.; Shi, S. Structure and Magnetic Investigation of a Series of Rare Earth Heterospin Monometallic Compounds of Nitronyl Nitroxide Radical. Zeitschrift fΓΌr Anorg. und Allg. Chemie 2016, 642, 148–154. [Google Scholar] [CrossRef]
  15. Kahn, M.L.; Sutter, J.-P.; Golhen, S.; Guionneau, P.; Ouahab, L.; Kahn, O.; Chasseau, D. Systematic Investigation of the Nature of the Coupling between a Ln(III) Ion (Ln = Ce(III) to Dy(III)) and Its Aminoxyl Radical Ligands. Structural and Magnetic Characteristics of a Series of {Ln(Radical)2} Compounds and the Related {Ln(Nitrone)2} Derivat. J. Am. Chem. Soc. 2000, 122, 3413–3421. [Google Scholar] [CrossRef]
  16. Lv, X.-H.; Yang, S.-L.; Li, Y.-X.; Zhang, C.-X.; Wang, Q.-L. A Family of Lanthanide Compounds Based on Nitronyl Nitroxide Radicals: Synthesis, Structure, Magnetic and Fluorescence Properties. RSC Adv. 2017, 7, 38179–38186. [Google Scholar] [CrossRef]
  17. Fan, Z.; Hou, Y.-F.; Wang, S.-P.; Yang, S.-T.; Zhang, J.-J.; Shi, S.-K.; Geng, L.-N. Synthesis, Crystal Structure, and Magnetic Property of New Trispin Ln(III)-Nitronyl Nitroxide Complexes. Helv. Chim. Acta 2016, 99, 732–741. [Google Scholar] [CrossRef]
  18. Wang, Y.-L.; Gao, Y.-Y.; Ma, Y.; Wang, Q.-L.; Li, L.-C.; Liao, D.-Z. Syntheses, Crystal Structures, Magnetic and Luminescence Properties of Five Novel Lanthanide Complexes of Nitronyl Nitroxide Radical. J. Solid State Chem. 2013, 202, 276–281. [Google Scholar] [CrossRef]
  19. Xu, J.-X.; Ma, Y.; Liao, D.; Xu, G.-F.; Tang, J.; Wang, C.; Zhou, N.; Yan, S.-P.; Cheng, P.; Li, L.-C. Four New Lanthanideβˆ’Nitronyl Nitroxide (LnIII = PrIII, SmIII, EuIII, TmIII) Complexes and a TbIII Complex Exhibiting Single-Molecule Magnet Behavior. Inorg. Chem. 2009, 48, 8890–8896. [Google Scholar] [CrossRef]
  20. Buchler, J.W.; De Cian, A.; Fischer, J.; Kihn-Botulinski, M.; Weiss, R. Metal Complexes with Tetrapyrrole Ligands. 46. Europium(III) Bis(Octaethylporphyrinate), a Lanthanoid Porphyrin Sandwich with Porphyrin Rings in Different Oxidation States, and Dieuropium(III) Tris(Octaethylporphyrinate). Inorg. Chem. 1988, 27, 339–345. [Google Scholar] [CrossRef]
  21. Klementyeva, S.V.; Gritsan, N.P.; Khusniyarov, M.M.; Witt, A.; Dmitriev, A.A.; Suturina, E.A.; Hill, N.D.D.; Roemmele, T.L.; Gamer, M.T.; BoerΓ©, R.T.; et al. The First Lanthanide Complexes with a Redox-Active Sulfur Diimide Ligand: Synthesis and Characterization of [LnCp*2(RN=)2S], Ln=Sm, Eu, Yb; R=SiMe3. Chem. - A Eur. J. 2017, 23, 1278–1290. [Google Scholar] [CrossRef]
  22. Caneschi, A.; Dei, A.; Gatteschi, D.; Poussereau, S.; Sorace, L. Antiferromagnetic Coupling between Rare Earth Ions and Semiquinones in a Series of 1 ∢ 1 Complexes. Dalt. Trans. 2004, 1048–1055. [Google Scholar] [CrossRef] [PubMed]
  23. Dei, A.; Gatteschi, D.; PΓ©caut, J.; Poussereau, S.; Sorace, L.; Vostrikova, K. Crystal Field and Exchange Effects in Rare Earth Semiquinone Complexes. Comptes Rendus l’Academie des Sci. - Ser. IIC Chem. 2001, 4. [Google Scholar] [CrossRef]
  24. Gaft, M.; Reisfeld, R.; Panczer, G. Modern Luminescence Spectroscopy of Minerals and Materials; Springer-Verlag: Berlin/Heidelberg, 2005; ISBN 3-540-21918-8. [Google Scholar]
  25. Machado, K.; Mukhopadhyay, S.; Videira, R.A.; Mishra, J.; Mobin, S.M.; Mishra, G.S. Polymer Encapsulated Scorpionate Eu3+ Complexes as Novel Hybrid Materials for High Performance Luminescence Applications. RSC Adv. 2015, 5, 35675–35682. [Google Scholar] [CrossRef]
  26. Binnemans, K. Interpretation of Europium(III) Spectra. Coord. Chem. Rev. 2015, 295, 1–45. [Google Scholar] [CrossRef]
  27. BΓΌnzli, J.-C.G. On the Design of Highly Luminescent Lanthanide Complexes. Coord. Chem. Rev. 2015, 293–294, 19–47. [Google Scholar] [CrossRef]
  28. Sorace, L.; Gatteschi, D. Electronic Structure and Magnetic Properties of Lanthanide Molecular Complexes. In Lanthanides and Actinides in Molecular Magnetism; Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, Germany, 2015; pp. 1–26. [Google Scholar]
  29. Andruh, M.; Bakalbassis, E.; Kahn, O.; Trombe, J.C.; Porcher, P. Structure, Spectroscopic and Magnetic Properties of Rare Earth Metal(III) Derivatives with the 2-Formyl-4-Methyl-6-(N-(2-Pyridylethyl)Formimidoyl)Phenol Ligand. Inorg. Chem. 1993, 32, 1616–1622. [Google Scholar] [CrossRef]
  30. Huang, J.; Loriers, J.; Porcher, P.; Teste de Sagey, G.; Caro, P.; Levy-Clement, C. Crystal Field Effect and Paramagnetic Susceptibility of Na5Eu(MoO4)4 and Na5Eu(WO4)4. J. Chem. Phys. 1984, 80, 6204–6209. [Google Scholar] [CrossRef]
  31. Caro, P.; Porcher, P. The Paramagnetic Susceptibility of C-Type Europium Sesquioxide. J. Magn. Magn. Mater. 1986, 58, 61–66. [Google Scholar] [CrossRef]
  32. Sella, A.; Brown, S.E.; Steed, J.W.; Tocher, D.A. Synthesis and Solid-State Structures of Pyrazolylmethane Complexes of the Rare Earths. Inorg. Chem. 2007, 46, 1856–1864. [Google Scholar] [CrossRef]
  33. Chen, S.-J.; Li, Y.-Z.; Chen, X.-T.; Shi, Y.-J.; You, X.-Z. Tetrabutylammonium Tetrakis(Nitrato-ΞΊ2O,Oβ€²)[1,3,5-Tris(Pyrazolyl) Methane-ΞΊ3N]Cerate(III). Acta Crystallogr. Sect. E Struct. Reports Online 2002, 58, m753–m755. [Google Scholar] [CrossRef]
  34. Bagnall, K.W.; Tempest, A.C.; Takats, J.; Masino, A.P. Lanthanoid Poly(Pyrazol-1-yl) Borate Complexes. Inorg. Nucl. Chem. Lett. 1976, 12, 555–557. [Google Scholar] [CrossRef]
  35. Stainer, M.V.R.; Takats, J. X-Ray Crystal and Molecular Structure of Tris[Hydridotris(Pyrazol-1-yl)Borato]Ytterbium(III), Yb(HBPz3)3. Inorg. Chem. 1982, 21, 4050–4053. [Google Scholar] [CrossRef]
  36. Apostolidis, C.; Rebizant, J.; Kanellakopulos, B.; von Ammon, R.; Dornberger, E.; MΓΌller, J.; Powietzka, B.; Nuber, B. Homoscorpionates (Hydridotris(1-Pyrazolyl)Borato Complexes) of the Trivalent 4fions. The Crystal and Molecular Structure of [(HB(N2C3H3)3]3LnIII, (Ln = Pr, Nd). Polyhedron 1997, 16, 1057–1068. [Google Scholar] [CrossRef]
  37. Apostolidis, C.; Rebizant, J.; Walter, O.; Kanellakopulos, B.; Reddmann, H.; Amberger, H.-D. Zur Elektronenstruktur Hochsymmetrischer Verbindungen Der F-Elemente. 35 [1] Kristall- Und MolekΓΌlstrukturen von Tris(Hydrotris(1-Pyrazolyl)Borato)-Lanthanid(III) (LnTp3; Ln = La, Eu) Sowie Elektronenstruktur von EuTp3. Zeitschrift fΓΌr Anorg. und Allg. Chemie 2002, 628, 2013–2025. [Google Scholar] [CrossRef]
  38. Apostolidis, C.; KovΓ‘cs, A.; Morgenstern, A.; Rebizant, J.; Walter, O. Tris-{Hydridotris(1-Pyrazolyl)Borato}lanthanide Complexes: Synthesis, Spectroscopy, Crystal Structure and Bonding Properties. Inorganics 2021, 9, 44. [Google Scholar] [CrossRef]
  39. Reger, D.L.; Knox, S.J.; Lindeman, J.A.; Lebioda, L. Poly(Pyrazolyl) Borate Complexes of Terbium, Samarium, and Erbium. X-Ray Crystal Structure of {[Ξ·3-HB(Pz)3]2Sm(Β΅-O2CPh)}2 (Pz = Pyrazolyl Ring). Inorg. Chem. 1990, 29, 416–419. [Google Scholar] [CrossRef]
  40. Chowdhury, T.; Evans, M.J.; Coles, M.P.; Bailey, A.G.; Peveler, W.J.; Wilson, C.; Farnaby, J.H. Reduction Chemistry Yields Stable and Soluble Divalent Lanthanide Tris(Pyrazolyl)Borate Complexes. Chem. Commun. 2023, 59, 2134–2137. [Google Scholar] [CrossRef]
  41. Qi, H.; Zhao, Z.; Zhan, G.; Sun, B.; Yan, W.; Wang, C.; Wang, L.; Liu, Z.; Bian, Z.; Huang, C. Air Stable and Efficient Rare Earth Eu(II) Hydro-Tris(Pyrazolyl)Borate Complexes with Tunable Emission Colors. Inorg. Chem. Front. 2020, 7, 4593–4599. [Google Scholar] [CrossRef]
  42. Long, J.; Lyubov, D.M.; Mahrova, T.V.; Cherkasov, A. V.; Fukin, G.K.; Guari, Y.; Larionova, J.; Trifonov, A.A. Synthesis, Structure and Magnetic Properties of Tris(Pyrazolyl)Methane Lanthanide Complexes: Effect of the Anion on the Slow Relaxation of Magnetization. Dalt. Trans. 2018, 47, 5153–5156. [Google Scholar] [CrossRef]
  43. Chowdhury, T.; Horsewill, S.J.; Wilson, C.; Farnaby, J.H. Heteroleptic Lanthanide(III) Complexes: Synthetic Utility and Versatility of the Unsubstituted Bis-Scorpionate Ligand Framework. Aust. J. Chem. 2022, 75, 660–675. [Google Scholar] [CrossRef]
  44. Llunell, M.; Casanova, D.; Cirera, J.; Alemany, P.; Alvarez, S. SHAPE, Version 2.1, Program for the Stereochemical Analysis of Molecular Fragments by Means of Continuous Shape Measures and Associated Tools. Univ. Barcelona, Barcelona, Spain 2013, 2103. [Google Scholar]
  45. Rousset, E.; Piccardo, M.; Gable, R.W.; Massi, M.; Sorace, L.; Soncini, A.; Boskovic, C. Elucidation of LMCT Excited States for Lanthanoid Complexes: A Theoretical and Solid-State Experimental Framework. Inorg. Chem. 2022. [Google Scholar] [CrossRef] [PubMed]
  46. Arauzo, A.; Lazarescu, A.; Shova, S.; BartolomΓ©, E.; Cases, R.; LuzΓ³n, J.; BartolomΓ©, J.; Turta, C. Structural and Magnetic Properties of Some Lanthanide (Ln = EuIII, GdIII and NdIII) Cyanoacetate Polymers: Field-Induced Slow Magnetic Relaxation in the Gd and Nd Substitutions. Dalt. Trans. 2014, 43, 12342–12356. [Google Scholar] [CrossRef] [PubMed]
  47. Wu, M.-F.; Wang, M.-S.; Guo, S.-P.; Zheng, F.-K.; Chen, H.-F.; Jiang, X.-M.; Liu, G.-N.; Guo, G.-C.; Huang, J.-S. Photoluminescent and Magnetic Properties of a Series of Lanthanide Coordination Polymers with 1-H-Tetrazolate-5-Formic Acid. Cryst. Growth Des. 2011, 11, 372–381. [Google Scholar] [CrossRef]
  48. Li, Y.; Zheng, F.-K.; Liu, X.; Zou, W.-Q.; Guo; Lu, C. -Z.; Huang, J.-S. Crystal Structures and Magnetic and Luminescent Properties of a Series of Homodinuclear Lanthanide Complexes with 4-Cyanobenzoic Ligand. Inorg. Chem. 2006, 45, 6308–6316. [Google Scholar] [CrossRef]
  49. Xu, N.; Wang, C.; Shi, W.; Yan, S.-P.; Cheng, P.; Liao, D.-Z. Magnetic and Luminescent Properties of Sm, Eu, Tb, and Dy Coordination Polymers with 2-Hydroxynicotinic Acid. Eur. J. Inorg. Chem. 2011, 2011, 2387–2393. [Google Scholar] [CrossRef]
  50. Han, M.; Li, S.; Ma, L.; Yao, B.; Feng, S.-S.; Zhu, M. Luminescent and Magnetic Bifunctional Coordination Complex Based on a Chiral Tartaric Acid Derivative and Europium. Acta Crystallogr. Sect. C Struct. Chem. 2019, 75, 1220–1227. [Google Scholar] [CrossRef]
  51. De Oliveira Maciel, J.W.; Lemes, M.A.; Valdo, A.K.; Rabelo, R.; Martins, F.T.; Queiroz Maia, L.J.; de Santana, R.C.; Lloret, F.; Julve, M.; Cangussu, D. Europium(III), Terbium(III), and Gadolinium(III) Oxamato-Based Coordination Polymers: Visible Luminescence and Slow Magnetic Relaxation. Inorg. Chem. 2021, 60, 6176–6190. [Google Scholar] [CrossRef]
  52. Vaz, R.C.A.; Esteves, I.O.; Oliveira, W.X.C.; Honorato, J.; Martins, F.T.; Marques, L.F.; dos Santos, G.L.; Freire, R.O.; Jesus, L.T.; Pedroso, E.F.; et al. Mononuclear Lanthanide(III)-Oxamate Complexes as New Photoluminescent Field-Induced Single-Molecule Magnets: Solid-State Photophysical and Magnetic Properties. Dalt. Trans. 2020, 49, 16106–16124. [Google Scholar] [CrossRef]
  53. Shintoyo, S.; Fujinami, T.; Matsumoto, N.; Tsuchimoto, M.; Weselski, M.; BieΕ„ko, A.; Mrozinski, J. Synthesis, Crystal Structure, Luminescent and Magnetic Properties of Europium(III) and Terbium(III) Complexes with a Bidentate Benzoate and a Tripod N7 Ligand Containing Three Imidazole, [LnIII(H3L)Benzoate](ClO4)2Β·H2OΒ·2MeOH (LnIII=EuIII and TbIII). Polyhedron 2015, 91, 28–34. [Google Scholar] [CrossRef]
  54. Benelli, C.; Caneschi, A.; Gatteschi, D.; Pardi, L.; Rey, P. Structure and Magnetic Properties of Linear-Chain Complexes of Rare-Earth Ions (Gadolinium, Europium) with Nitronyl Nitroxides. Inorg. Chem. 1989, 28, 275–280. [Google Scholar] [CrossRef]
  55. Liu, R.; Zhao, S.; Xiong, C.; Xu, J.; Li, Q.; Fang, D. Three New One-Dimensional Lanthanide Complexes Bridged by Nitronyl Nitroxide Radicals: Crystal Structures and Magnetic Characterization. J. Mol. Struct. 2013, 1036, 107–110. [Google Scholar] [CrossRef]
  56. Mei, X.; Wang, X.; Wang, J.; Ma, Y.; Li, L.; Liao, D. Dinuclear Lanthanide Complexes Bridged by Nitronyl Nitroxide Radical Ligands with 2-Phenolate Groups: Structure and Magnetic Properties. New J. Chem. 2013, 37, 3620–3626. [Google Scholar] [CrossRef]
  57. Zhu, M.; Jia, L.; Li, Y.; Li, Y.; Zhang, L.; Zhang, W.; LΓΌ, Y. Nitronyl Nitroxide Bridged 3d–4f Hetero-Tri-Spin Chains: Synthesis Strategy, Crystal Structure and Magnetic Properties. CrystEngComm 2018, 20, 420–431. [Google Scholar] [CrossRef]
  58. Bain, G.A.; Berry, J.F. Diamagnetic Corrections and Pascal’s Constants. J. Chem. Educ. 2008, 85, 532. [Google Scholar] [CrossRef]
  59. Apex3 Software Suite: Apex3, SADABS-2016/2 and SAINT 8.40a; Publisher: Bruker AXS Inc. 2017.
  60. Sheldrick, G.M. SHELXT – Integrated Space-Group and Crystal-Structure Determination. Acta Crystallogr. Sect. A Found. Adv. 2015, 71, 3–8. [Google Scholar] [CrossRef]
  61. Sheldrick, G.M. Crystal Structure Refinement with SHELXL. Acta Crystallogr. Sect. C Struct. Chem. 2015, 71, 3–8. [Google Scholar] [CrossRef]
  62. Dolomanov, O.V.; Bourhis, L.J.; Gildea, R.J.; Howard, J.A.K.; Puschmann, H. OLEX2 : A Complete Structure Solution, Refinement and Analysis Program. J. Appl. Crystallogr. 2009, 42, 339–341. [Google Scholar] [CrossRef]
Preprints 83275 sch001
Scheme 1. The tripodal ligands: (a) 4,4-dimethyl-2,2-bis(pyridin-2-yl)-1,3-oxazolidine-3-oxyl (Rad); (b) Trispyrazolylmethane (HCPz3); (b) tris(3,5-dimethyl-1-pyrazolyl)methane (HC(PzMe2)3).
Scheme 1. The tripodal ligands: (a) 4,4-dimethyl-2,2-bis(pyridin-2-yl)-1,3-oxazolidine-3-oxyl (Rad); (b) Trispyrazolylmethane (HCPz3); (b) tris(3,5-dimethyl-1-pyrazolyl)methane (HC(PzMe2)3).
Preprints 83275 sch001
Preprints 83275 g001
Figure 1. The asymmetric units in the crystal structure of: (a) [Eu(HCPz3)(NO3)3H2O]Ξ‡2MeCN (1); (b) [Eu(HCPz3)(NO3)3H2O] (1a).
Figure 1. The asymmetric units in the crystal structure of: (a) [Eu(HCPz3)(NO3)3H2O]Ξ‡2MeCN (1); (b) [Eu(HCPz3)(NO3)3H2O] (1a).
Preprints 83275 g001
Preprints 83275 g002
Figure 2. (a) An asymmetric unit in the crystal structure of [Eu(HC(PzMe2)3)(NO3)3]Ξ‡MeCN (2); (b) A dimer organization for Eu01 site in the crystal structure of [Eu(HCPz3)H2O(CF3SO3)3]2 (3).
Figure 2. (a) An asymmetric unit in the crystal structure of [Eu(HC(PzMe2)3)(NO3)3]Ξ‡MeCN (2); (b) A dimer organization for Eu01 site in the crystal structure of [Eu(HCPz3)H2O(CF3SO3)3]2 (3).
Preprints 83275 g002
Preprints 83275 g003
Figure 3. The Ο‡MT versus T data (β—‹) measured at the applied magnetic field H = 1 kOe. The blue lines show the best fits to the data of Eq. (4) with the spin-orbit coupling Ξ» being the only adjustable parameter; resulting values of Ξ» are presented in Table 2.
Figure 3. The Ο‡MT versus T data (β—‹) measured at the applied magnetic field H = 1 kOe. The blue lines show the best fits to the data of Eq. (4) with the spin-orbit coupling Ξ» being the only adjustable parameter; resulting values of Ξ» are presented in Table 2.
Preprints 83275 g003
Preprints 83275 g004
Figure 4. Field dependences of the magnetization measured for 1-3 at T = 1.77 K.
Figure 4. Field dependences of the magnetization measured for 1-3 at T = 1.77 K.
Preprints 83275 g004
Table 1. The coordination polyhedron bond and Eu …. Eu distances (Γ…) in the studied compounds.
Table 1. The coordination polyhedron bond and Eu …. Eu distances (Γ…) in the studied compounds.
1 1a 2 3
Eu11 Eu21
Euβ€”N 2.5810(12) 2.5678(16) 2.5402(19) Eu1β€”N1 2.520(8) Eu2β€”N7 2.533(8)
2.5926(12) 2.5180(17) 2.5592(19) Eu1β€”N3 2.537(8) Eu2β€”N9 2.542(9)
2.5932(12) 2.6072(16) 2.5158(18) Eu1β€”N5 2.552(8) Eu2β€”N11 2.552(9)
mean 2.5889 2.5643 2.5384 5.36 5.42
Euβ€”Oanion 2.5687(11) 2.4909(14) 2.4440(17) Eu1β€”O1 2.378(6) Eu2β€”O11 2.382(7)
2.4846(10) 2.7172(16) 2.4883(17) Eu1β€”O3i 2.404(6) Eu2β€”O14 2.520(8)
2.5153(11) 2.4288(13) 2.4718(17) Eu1β€”O4 2.376(6) Eu2β€”O17 2.537(8)
2.4655(11) 2.4983(15) 2.4465(17) Eu1β€”O7 2.334(6) Eu2β€”O19ii 2.552(8)
2.5234(11) 2.5306(15) 2.4674(17) mean 2.373 mean 2.498
2.5005(11) 2.5199(15) 2.4514(17)
mean 2.5097 2.5310 2.4616
Euβ€”Oaqua 2.4191(11) 2.4237(15) Eu1β€”O10 2.382(7) Eu2β€”O20 2.360(8)
Eu …. Eu 6.151 6.646 8.931 6.137 6.073
1 Symmetry codes for compound 3: (i) βˆ’x+3, βˆ’y+2, βˆ’z+2; (ii) βˆ’x+2, βˆ’y+2, βˆ’z+2.
Table 2. Magnetic parameters for europium(III) molecular compounds.
Table 2. Magnetic parameters for europium(III) molecular compounds.
Compound Ο‡MT (emuΞ‡K/mol) Ξ» (cm–1)a Rb Reference
2 K 300 K
Free Eu3+ 0 1.280 220–380 [21,45]
1 0.0113 1.228 406 1.02Γ—10–4 this work
2 0.0114 1.251 396 4.10Γ—10–5 this work
3/Eu 0.0120 1.255 383 3.26Γ—10-4 this work
[Eu2(L1)6(H2O)4]n/Eu 0.025 1.325 343/360c [46]
[Eu2(tzf)3(H2O)6]n/Eu 0.020 1.388 344 2.7Γ—10-4 [47]
[Eu2L26Pen2(H2O)2]/Eu 404/379d 3.1Γ—10-4 [48]
[EuL3(H2O)2SO4]n 336 4.28Γ—10–4 [49]
[EuL43(CH3OH)3]n 360 9.65Γ—10–5 [50]
[Eu2(Hpcpa)3(H2O)5]n sap 1.2 356/351c 2.2Γ—10–5 [51]
[Eu(HLCl)4(dmso)]βˆ’ 1.37 348 4.1Γ—10βˆ’5 [52]
[Eu(HLF)4(dmso)]βˆ’ 1.37 336 2.1Γ—10βˆ’5 [52]
[EuL52(H2O)4](ClO4)3] 362/370c 7.0Γ—10–4 [29]
[Eu(trippBAP)3] 363 [6]
[EuL6PhCOO](ClO4)2 0.015 1.30 370/410d [53]
[Eu(Nitrone)2(NO3)3] 1.25 371.5 [15]
[Eu(HBPz3)2Trp] 0.037 1.48 [22]
[Eu(hfac)3NNe] 0.192 1.946 332 2.0Γ—10βˆ’3 [19]
Eu(OEP)2–(OEP)–] 0.208 1.575 [20]
[EuIII(AP2–)(ISQ)–] 0.252 1.834 [21]
[Eu(HBPz3)2SQ] 0.28 1.59 [22]
[Eu(hfac)3NN2]SMMTb 0.035 2.24 259 [12]
[Eu(hfac)3PhOMeNN2] 0.11 1.89 [13]
[Eu(hfac)3NN2] 0.12 1.98 309 [14]
[EuNNtrz2(NO3)3] 0.24 1.93 [15]
[Eu(hfac)3NN2] 0.419 3.09 [16]
[Eu(hfac)3NN2] 2.38 175 [17]
[Eu(hfac)3NN2] 2.12 331 [18]
[EuRad2(OTf)3] 0.348 1.78 [11]
[Eu(hfac)3NNEt]n 0.89 1.9 [54]
[Eu(hfac)3NN]n 1.88 267 1.47Γ—10βˆ’4 [55]
[Eu2(acac)4PhONN2] 0.66 3.47 326 2.67Γ—10-5 [56]
[NN4CuL2(Eu(hfac)3)3] 0.38 5.78 1.8 ×10–3 [57]
a Spin-orbit coupling parameter; b Agreement factor; c Found from optic data at 77 K; d found from optic data at RT; e NN is nitronyl nitroxide type radical ligand.
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.
Copyright: This open access article is published under a Creative Commons CC BY 4.0 license, which permit the free download, distribution, and reuse, provided that the author and preprint are cited in any reuse.
Prerpints.org logo

Preprints.org is a free preprint server supported by MDPI in Basel, Switzerland.

facebook logotwitter logolinkedin logo
MDPI Initiatives
Important Links
Subscribe

Disclaimer

Terms of Use

Privacy Policy

Β© 2024 MDPI (Basel, Switzerland) unless otherwise stated