1. Introduction

2. Results

2.2. DFT Calculations

In order to elucidate the molecular structures of fragment ions detected in mass spectrometry experiments, a series of DFT calculations has been performed, starting from the computation of the minimum energy structures of the three neutral complexes [Ni(L)₂TMEDA] (Figure 3). Additionally, all fragments discussed in the previous section have been subjected to structural optimizations. The resulting optimized geometries are depicted in Figure 3, Figure 4, Figures S1 and S2, while relevant geometrical parameters are reported in Table 2 2, Table 4 and Table S1.

A graphical representation of the optimized structures of the neutral complexes obtained for L= tfa, fod, and thd is shown in Figure 3a,c,e, respectively. Since all ESI-HRMS spectra showed a base peak due to the loss of a β-diketonate ligand L, a search for the minimum energy structures of [M-L]⁺ species has been performed starting from the optimized structures of neutral complexes and removing a β-diketonate ligand. The resulting optimized geometries of [Ni(L)TMEDA]⁺ with L = tfa, fod, and thd are depicted in Figure 3b,d,f, respectively.

As far as the neutral complexes are concerned, their molecular geometries are similar among each other and close to the structural parameters computed with another density functional approximation [32]. In particular, in all the three neutral complexes Ni exhibits a slightly distorted octahedral coordination environment, characterized by Ni-O distances shorter than Ni-N ones (see Table 2), suggesting that the interactions between metal center and oxygen atoms should be stronger than those with nitrogen ones. This hypothesis is substantiated by the bond order (BO) trend, as the Ni-O BOs are systematically higher than the Ni-N ones for all three compounds (see Table 2). Interestingly, whereas BO values for Ni-O bonds are quite similar among the three complexes, the Ni-N bond order for the non-fluorinated compound 3 - bearing two tert-butyl group per diketonate ligand - is slightly lower than that found for fluorinated complexes 1 and 2. These data indicate that, whereas F-containing groups cope to increase the Ni-N bond strength, the presence of tert-butyl substituents has the opposite effect – i.e., weakening Ni-N interactions. Nonetheless, beside these slight differences, both the molecular geometry and the electronic structure underlying the metal-ligand bonding scheme show a strong similarity in the three compounds, as evidenced by Figure 3 and the data in Table 2. This result might rationalize the similar fragmentation behavior of the target complexes as deduced from Figure 1, in particular the presence of [M-L]⁺ as the base peak in all ESI-HRMS spectra.

Indeed, similar considerations hold for the minimum energy structures calculated for [M-L]⁺ fragments, all characterized by very similar geometric arrangements and metal-ligand bonding schemes. Specifically, as illustrated by Figure 3b,d,f, all three ions are characterized by a square-planar geometry, typical of tetra-coordinated Ni(II) complexes in the singlet spin state. Moreover, data in Table 2 indicate that both geometrical parameters and BOs values show only very slight differences in passing from compound 1 to 2 to 3. This finding is further supported by the Natural Bond Orbital (NBO) analysis performed on the electronic structure of the three [M-L]⁺ fragments. In particular, the data reported in Table S2 indicate a very strong similarity of the NBOs localized on the metal-ligand bonds. Irrespective of the diketonate nature, all NBOs have σ-character. While the bonding components (BD(σ)) are mostly localized on ligand’s nitrogen and oxygen atoms (≈90%), the antibonding components (BD(σ*)) are predominantly localized on Ni. Taken together, NBO data indicate that electron charge is transferred by the ligands towards Ni. This finding is further clarified by the graphical representation of the aforementioned bonding NBO’s - depicted in Figures S3, S4, and S5 for L = tfa, fod, and thd, respectively –, highlighting the net σ-character of the orbital, as well as Ni participation to the bonding scheme. Such a close similarity in the electronic structure might suggest that all three ions are characterized by a similar stability and may all easily form in ESI-HRMS conditions.

Notably, for all the target complexes, Ni-O and Ni-N distances undergo a significant shortening upon passing from neutral compounds to [M-L]⁺ fragments. This trend is paralleled by the considerable increase of the corresponding bond orders, which are nearly doubled in the fragment ions. Hence, in terms of the metal-ligand bonding, the loss of a diketonate ligand results in a significant strengthening of Ni-TMEDA interactions and of Ni-O bonds of the remaining diketonate moiety.

A useful feature of NBO analysis is the opportunity of partitioning the electronic density between ‘subsystems’ – i.e., specific portions of a given molecule, allowing thus to estimate the total charge on each subsystem. In this case, it is particularly instructive to inspect the total NBO charges localized on Ni, diketonate ligand L, and TMEDA, reported in Table 3. Interestingly, the data show that the positive charge on Ni decreases by ≈ 25-30% on passing from neutral complex to [M-L]⁺ cations. This result, that may appear counterintuitive given the fragments’ positive charge, may be explained by considering that the donation of electronic charge from both L and TMEDA to Ni increases significantly upon the loss of a diketonate ligand. Indeed, the total negative charge on L decreases by 50%, whereas the total (positive) charge on TMEDA is more than doubled (Table 3). Hence, these data clearly indicate that all [M-L]⁺ species are stabilized by a strong donation of electronic density from the ligands towards the metal center. This effect is slightly stronger in the fragment derived from compound 3, due to the higher electron-donor character of the two tert-butyl substituents on the diketonate moiety with respect to fluorine-containing groups, present in compounds 1-2.

Beside the main peak, which is common to the three complexes, ESI-HRMS spectra indicated the formation of other cations (see Figure 1 and Table 1). A careful computational search of the minimum energy structure of these species has been performed as well. Graphical representations of optimized geometries of [M+Na]⁺, [M-TMEDA+Na]⁺, [M-TMEDA+H]⁺, [HL+H]⁺ and [TMEDA+H]⁺ are shown in Figure S1, while selected geometrical parameters are reported in Table S1. It should be pointed out that Na⁺ is present only in ESI-HRMS spectra of the fluorine-richest compound 2. In [M+Na]⁺, Ni maintains its octahedral environment in spite of the entrance of Na⁺ in the second coordination shell (Figure S1a). Specifically, three O atoms appear to be at coordination distances from Na (average Na-O distance = 2.416 Å), which is also interacting with a fluorine atom (Na-F distance = 2.441 Å). The consequent distortion of the octahedral Ni environment is evidenced by the lengthening of Ni-O and Ni-N bonds with respect to the neutral complex [Ni(fod)₂TMEDA]. This effect is particularly relevant for the bonds involving the three oxygen atoms also coordinated with Na⁺ (Table S1). Similarly, the species [M-TMEDA+Na]⁺ - exhibiting a distorted square-planar Ni coordination geometry, is characterized by significant O-Na⁺ and F-Na+ interactions (Table S1, Figure S1b). In a different way, the [M-TMEDA+H]⁺ species - namely [Ni(thd)₂+H]⁺ - is protonated at the CH1 carbon. For this ion, two structures very close in energy (ΔE = 0.32 kcal/mol) have been found (Figure S1c,d). The most stable one exhibits a distorted tetrahedral arrangement around the Ni center, and has triplet spin multiplicity, whereas the less stable one shows a distorted square planar arrangement and singlet spin multiplicity. Given the modest energy difference, both structures might be formed during the ESI process. The presence of the protonated diketonate species [HL+H]⁺ has been detected only for the case of the more electron-donor thd ligand. Its optimized structure is characterized by the protonation of both carbonylic groups (Figure S1e). On the other hand, the other protonated ligand [TMEDA+H]⁺ is detected in the fragmentation of all three complexes. In this case, the protonation occurs on one of the nitrogen atoms (see Figure S1f).

As far as MS² spectra are concerned, attention was focused on the subsequent fragmentation of [M-L]⁺ cations. Even in this case, the spectra of the three cations presented common features, in particular the formation of [M-L]⁺ - NH(CH₃)₂ species. The theoretical search of the minimum energy structure of these moieties led to the molecular geometries depicted in Figure 4a,c,f for L = tfa, fod, thd, respectively. Remarkably, these cations have very similar geometries and Ni-ligands bonding patterns. Whereas the diketonate remains coordinated to Ni with both its oxygen atoms, only one nitrogen atom (the one survived to the fragmentation) is linked to the metal center. Nevertheless, Ni maintains its nearly square-planar coordination geometry thanks to the interaction with a double C=C bond formed upon - NH(CH₃)₂ release. Specifically, the Ni-CHT and Ni-CH2T distances become ≈ 2 Å in these fragments (see Table 4). Moreover, data in Table 4 clearly indicate a net shortening of CHT-CH2T bond length (Figure 4) compared to the same distance in [M-L]⁺ species (Table 2). This distance shortening is accompanied by a significant increase of the CHT-CH2T bond order (from values of ≈ 1 to values greater than 1.5, see Table 2 and Table 4). Correspondingly, Ni-CHT and Ni-CH2T BOs values become comparable to those of Ni-O/Ni-N bonds, indicating appreciable Ni-C interactions which are greater for the terminal C atom (CH2T), closer to Ni. These observations are common to the three cations, underlining once again the similarity of the metal-ligand bonding scheme among systems derived from compounds 1, 2, 3.

The loss of a -CH₃CH₂N(CH₃)₂ group is detected only for the fluorinated [M-L]⁺ species derived from complexes 1 and 2. In these cations (see Figure 4 b,d), the bonding pattern around Ni is practically the same as in [M-L]⁺ - NH(CH₃)₂ species, discussed previously. The planar tetra-coordinated Ni structure is characterized by two Ni-O bonds, one Ni-N bond and a cation-π intramolecular interaction between the Ni center and the CHT=CH2T double bond. Figures S6-S10 report a graphical representation of the relevant orbitals involved in this cation-π interaction, whereas Tables S3 and S4 report the quantitative NBO analysis. As can be seen from both orbital representations and NBO analysis, Ni cation actively participates to such an interaction, with the π structure predominantly localized on the CHT=CH2T double bond.

Concerning complex 2, species corresponding to the loss of a CH₃C=CH₂ group from [Ni(fod)TMEDA]⁺ have been detected ([Ni(fod)TMEDA]⁺-(CH₃)₂C=CH₂) in ESI-MS spectra. Their stoichiometry indicates a rearrangement of the fod ligand (see Figure 1 and Table 1). In order to identify the structure of these cations, geometry optimizations have been performed on different hypothetical guess structures characterized by such a stoichiometry. Figure S2 contains a graphical representation of the six most stable structures, along with their relative stability (including the zero-point contribution). The most stable structure (Figure S2a) is characterized by a distribution of fluorine atoms on both diketonate ligand sides. A similar feature is also present in the other lower energy isomers.

Finally, the trend of the Bader charges on passing form the neutral complex to the positive ions further evidences common features in the fragmentation of the three complexes (see Tables S5-S8). Indeed, it is possible to deduce a displacement of electrons from ligands to the metal center, whose positive charge is significantly depleted along the fragmentation. This finding is also in line with the arguments deduced from NBO analysis. Notably, such an electron-enrichment tendency of the metal center during [Ni(L)₂TMEDA] precursors’ fragmentation might be relevant for CVD processes, where an electron-richer Ni cation (nearly +1) could be more prone to be oxidized by the molecular oxygen present in the reaction atmosphere, facilitating thus the formation of NiO films.

Table 4. Selected bond lengths (BL) (in Å) and corresponding bond orders (BO) from the optimized structures of fragments detected in ESI-MS² spectra of [M-L]⁺ ions for compounds 1, 2, and 3. Different colors in the BO columns refer to different ligands (brown = diketonate, gray = TMEDA). Atom labels as in Figure 4.

Table 4. Selected bond lengths (BL) (in Å) and corresponding bond orders (BO) from the optimized structures of fragments detected in ESI-MS² spectra of [M-L]⁺ ions for compounds 1, 2, and 3. Different colors in the BO columns refer to different ligands (brown = diketonate, gray = TMEDA). Atom labels as in Figure 4.

Bond distance	1		2			33
	[M-tfa]+- NH(CH3)2	[M-tfa]+- CH3CH2N(CH3)2	[M-fod]+- NH(CH3)2	[M-fod]+- CH3CH2N(CH3)2	[M-fod]+-  -(CH3)2C=CH2	[M-thd]+- NH(CH3)2
	BL  BO	BL  BO	BL  BO	BL  BO	BL  BO	BL BO
Ni-O1	1.811 0.523	1.799 0.557	1.814 0.506	1.794 0.554	1.837 0.450	1.808 0.535
Ni-O2	1.830 0.511	1.819 0.541	1.816 0.518	1.815 0.543	1.842 0.453	1.803 0.546
Ni-N1	-	-	1.929 0.391	1.946 0.402	1.938 0.415	1.941 0.368
Ni-N2	1.932 0.393	1.943 0.408	2.153 0.201	1.947 0.387	1.937 0.414	1.957 0.368
Ni-CHT	1.972 0.248	1.987 0.264	1.976 0.239	1.986 0.264	2.165 0.178	1.974 0.243
Ni-CH2T	2.096 0.394	2.128 0.368	2.098 0.393	2.128 0.363	2.165 0.178	2.108 0.375
O1-C5	1.277 1.288	1.281 1.267	1.280 1.258	1.281 1.263	1.265 1.342	1.288 1.264
O2-C7	1.281 1.297	1.279 1.308	1.279 1.314	1.280 1.299	1.270 1.318	1.287 1.264
C5-CH1	1.384 1.444	1.381 1.463	1.380 1.468	1.381 1.458	1.400 1.345	1.399 1.381
C7-CH1	1.409 1.315	1.412 1.300	1.417 1.281	1.413 1.292	1.389 1.404	1.403 1.361
CHT-CH2T	1.379 1.566	1.373 1.588	1.380 1.567	1.373 1.590	1.508 1.027	1.378 1.579

3. Materials and Methods

4. Conclusions

References

1. Sialvi, M.Z.; Mortimer, R.J.; Wilcox, G.D.; Teridi, A.M.; Varley, T.S.; Wijayantha, K.G.U.; Kirk, C.A. Electrochromic and colorimetric properties of nickel(II) oxide thin films prepared by aerosol-assisted chemical vapor deposition. ACS Appl. Mater. Interfaces 2013, 5, 5675–5682. [Google Scholar] [CrossRef] [PubMed]
2. Wilson, R.L.; Macdonald, T.J.; Lin, C.-T.; Xu, S.; Taylor, A.; Knapp, C.E.; Guldin, S.; McLachlan, M.A.; Carmalt, C.J.; Blackman, C.S. Chemical vapour deposition (CVD) of nickel oxide using the novel nickel dialkylaminoalkoxide precursor [Ni(dmamp')₂] (dmamp' = 2-dimethylamino-2-methyl-1-propanolate). RSC Adv. 2021, 11, 22199–22205. [Google Scholar] [CrossRef] [PubMed]
3. Han, S.W.; Kim, I.H.; Kim, D.H.; Park, K.J.; Park, E.J.; Jeong, M.-G.; Kim, Y.D. Temperature regulated-chemical vapor deposition for incorporating NiO nanoparticles into mesoporous media. Appl. Surf. Sci. 2016, 385, 597–604. [Google Scholar] [CrossRef]
4. Kitchamsetti, N.; Ramteke, M.S.; Rondiya, S.R.; Mulani, S.R.; Patil, M.S.; Cross, R.W.; Dzade, N.Y.; Devan, R.S. DFT and experimental investigations on the photocatalytic activities of NiO nanobelts for removal of organic pollutants. J. Alloys Compd. 2021, 855, 157337. [Google Scholar] [CrossRef]
5. Zywitzki, D.; Taffa, D.H.; Lamkowski, L.; Winter, M.; Rogalla, D.; Wark, M.; Devi, A. Tuning coordination geometry of nickel ketoiminates and its influence on thermal characteristics for chemical vapor deposition of nanostructured NiO electrocatalysts. Inorg. Chem. 2020, 59, 10059–10070. [Google Scholar] [CrossRef] [PubMed]
6. An, W.-J.; Thimsen, E.; Biswas, P. Aerosol-chemical vapor deposition method for synthesis of nanostructured metal oxide thin films with controlled morphology. J. Phys. Chem. Lett. 2010, 1, 249–253. [Google Scholar] [CrossRef]
7. Weidler, N.; Schuch, J.; Knaus, F.; Stenner, P.; Hoch, S.; Maljusch, A.; Schäfer, R.; Kaiser, B.; Jaegermann, W. X-ray photoelectron spectroscopic investigation of plasma-enhanced chemical vapor deposited NiO_x, NiO_x(OH)_y, and CoNiO_x(OH)_y: influence of the chemical composition on the catalytic activity for the oxygen evolution reaction. J. Phys. Chem. C 2017, 121, 6455–6463. [Google Scholar] [CrossRef]
8. Hussain, N.; Yang, W.; Dou, J.; Chen, Y.; Qian, Y.; Xu, L. Ultrathin mesoporous F-doped α-Ni(OH)2 nanosheets as an efficient electrode material for water splitting and supercapacitors. J. Mater. Chem. A 2019, 7, 9656–9664. [Google Scholar] [CrossRef]
9. Mishra, S.; Daniele, S. Metal–organic derivatives with fluorinated ligands as precursors for inorganic nanomaterials. Chem. Rev. 2015, 115, 8379–8448. [Google Scholar] [CrossRef]
10. Bekermann, D.; Barreca, D.; Gasparotto, A.; Maccato, C. Multi-component oxide nanosystems by Chemical Vapor Deposition and related routes: challenges and perspectives. CrystEngComm 2012, 14, 6347–6358. [Google Scholar] [CrossRef]
11. Mishra, S.; Daniele, S. Molecular engineering of metal alkoxides for solution phase synthesis of high-tech metal oxide nanomaterials. Chem. Eur. J. 2020, 26, 9292–9303. [Google Scholar] [CrossRef] [PubMed]
12. Barreca, D.; Fois, E.; Gasparotto, A.; Maccato, C.; Oriani, M.; Tabacchi, G. The early steps of molecule-to-material conversion in chemical vapor deposition (CVD): a case study. Molecules 2021, 26, 1988. [Google Scholar] [CrossRef] [PubMed]
13. Klotzsche, M.; Barreca, D.; Bigiani, L.; Seraglia, R.; Gasparotto, A.; Vanin, L.; Jandl, C.; Pöthig, A.; Roverso, M.; Bogialli, S. , et al. Facile preparation of a cobalt diamine diketonate adduct as a potential vapor phase precursor for Co₃O₄ films. Dalton Trans. 2021, 50, 10374–10385. [Google Scholar] [CrossRef] [PubMed]
14. Barreca, D.; Bigiani, L.; Klotzsche, M.; Gasparotto, A.; Seraglia, R.; Jandl, C.; Pöthig, A.; Fois, E.; Vanin, L.; Tabacchi, G. , et al. A versatile Fe(II) diketonate diamine adduct: preparation, characterization and validation in the chemical vapor deposition of iron oxide nanomaterials. Mater. Chem. Phys. 2022, 277, 125534. [Google Scholar] [CrossRef]
15. Stienen, C.; Grahl, J.; Wölper, C.; Schulz, S.; Bendt, G. Fluorinated β-diketonate complexes M(tfac)₂(TMEDA) (M = Fe, Ni, Cu, Zn) as precursors for the MOCVD growth of metal and metal oxide thin films. RSC Adv. 2022, 12, 22974–22983. [Google Scholar] [CrossRef] [PubMed]
16. Utke, I.; Swiderek, P.; Höflich, K.; Madajska, K.; Jurczyk, J.; Martinović, P.; Szymańska, I.B. Coordination and organometallic precursors of group 10 and 11: focused electron beam induced deposition of metals and insight gained from chemical vapour deposition, atomic layer deposition, and fundamental surface and gas phase studies. Coord. Chem. Rev. 2022, 458, 213851. [Google Scholar] [CrossRef]
17. Utriainen, M.; Kröger-Laukkanen, M.; Johansson, L.-S.; Niinistö, L. Studies of metallic thin film growth in an atomic layer epitaxy reactor using M(acac)₂ (M=Ni, Cu, Pt) precursors. Appl. Surf. Sci. 2000, 157, 151–158. [Google Scholar] [CrossRef]
18. Lindahl, E.; Ottosson, M.; Carlsson, J.-O. Atomic layer deposition of NiO by the Ni(thd)₂/H₂O precursor combination. Chem. Vap. Deposition 2009, 15, 186–191. [Google Scholar] [CrossRef]
19. Lindahl, E.; Lu, J.; Ottosson, M.; Carlsson, J.O. Epitaxial NiO (100) and NiO (111) films grown by atomic layer deposition. J. Cryst. Growth 2009, 311, 4082–4088. [Google Scholar] [CrossRef]
20. Utriainen, M.; Kröger-Laukkanen, M.; Niinistö, L. Studies of NiO thin film formation by atomic layer epitaxy. Mater. Sci. Eng., B 1998, 54, 98–103. [Google Scholar] [CrossRef]
21. Chandrakala, M.; Raj Bharath, S.; Maiyalagan, T.; Arockiasamy, S. Synthesis, crystal structure and vapour pressure studies of novel nickel complex as precursor for NiO coating by metalorganic chemical vapour deposition technique. Mater. Chem. Phys. 2017, 201, 344–353. [Google Scholar] [CrossRef]
22. Emmenegger, F.; Schlaepfer, C.W.; Stoeckli-Evans, H.; Piccand, M.; Piekarski, H. Chelate effect in the gas phase. The complexes of Ni(2,2,6,6-tetramethyl-3,5-heptanedionate)₂ with bidentate ligands. Inorg. Chem. 2001, 40, 3884–3888. [Google Scholar] [CrossRef]
23. Maccato, C.; Bigiani, L.; Carraro, G.; Gasparotto, A.; Seraglia, R.; Kim, J.; Devi, A.; Tabacchi, G.; Fois, E.; Pace, G. , et al. Molecular engineering of Mn^II diamine diketonate precursors for the vapor deposition of manganese oxide nanostructures. Chem. Eur. J. 2017, 23, 17954–17963. [Google Scholar] [CrossRef]
24. Barreca, D.; Carraro, G.; Devi, A.; Fois, E.; Gasparotto, A.; Seraglia, R.; Maccato, C.; Sada, C.; Tabacchi, G.; Tondello, E. , et al. b-Fe2O3 nanomaterials from an iron(II) diketonate-diamine complex: a study from molecular precursor to growth process. Dalton Trans. 2012, 41, 149–155. [Google Scholar] [CrossRef]
25. Barreca, D.; Carraro, G.; Gasparotto, A.; Maccato, C.; Seraglia, R.; Tabacchi, G. An iron(II) diamine diketonate molecular complex: synthesis, characterization and application in the CVD of Fe₂O₃ thin films. Inorg. Chim. Acta 2012, 380, 161–166. [Google Scholar] [CrossRef]
26. Bandoli, G.; Barreca, D.; Gasparotto, A.; Maccato, C.; Seraglia, R.; Tondello, E.; Devi, A.; Fischer, R.A.; Winter, M. A cobalt(II) hexafluoroacetylacetonate ethylenediamine complex as a CVD molecular source of cobalt oxide nanostructures. Inorg. Chem. 2009, 48, 82–89. [Google Scholar] [CrossRef] [PubMed]
27. Gasparotto, A.; Barreca, D.; Devi, A.; Fischer, R.A.; Fois, E.; Gamba, A.; Maccato, C.; Seraglia, R.; Tabacchi, G.; Tondello, E. Innovative M(hfa)₂•TMEDA (M=Cu, Co) precursors for the CVD of copper-cobalt Oxides: an integrated theoretical and experimental approach. ECS Trans. 2009, 25, 549–556. [Google Scholar] [CrossRef]
28. Bandoli, G.; Barreca, D.; Gasparotto, A.; Seraglia, R.; Tondello, E.; Devi, A.; Fischer, R.A.; Winter, M.; Fois, E.; Gamba, A. , et al. An integrated experimental and theoretical investigation on Cu(hfa)₂•TMEDA: structure, bonding and reactivity. Phys. Chem. Chem. Phys. 2009, 11, 5998–6007. [Google Scholar] [CrossRef] [PubMed]
29. Fois, E.; Tabacchi, G.; Barreca, D.; Gasparotto, A.; Tondello, E. “Hot” surface activation of molecular complexes: insight from modeling studies. Angew. Chem. Int. Ed. 2010, 49, 1944–1948. [Google Scholar] [CrossRef]
30. Barreca, D.; Fois, E.; Gasparotto, A.; Seraglia, R.; Tondello, E.; Tabacchi, G. How does Cu^II convert into Cu^I? An unexpected ring-mediated single-electron reduction. Chem. Eur. J. 2011, 17, 10864–10870. [Google Scholar] [CrossRef]
31. Tabacchi, G.; Fois, E.; Barreca, D.; Gasparotto, A. CVD precursors for transition metal oxide nanostructures: molecular properties, surface behavior and temperature effects. Phys. Status Solidi A 2014, 211, 251–259. [Google Scholar] [CrossRef]
32. Benedet, M.; Barreca, D.; Fois, E.; Seraglia, R.; Tabacchi, G.; Roverso, M.; Pagot, G.; Invernizzi, C.; Gasparotto, A.; Heidecker, A.A. , et al. Interplay between coordination sphere engineering and properties of nickel diketonate–diamine complexes as vapor phase precursors for the growth of NiO thin films. Dalton Trans. 2023, 52, 10677–10688. [Google Scholar] [CrossRef] [PubMed]
33. Benedet, M.; Maccato, C.; Pagot, G.; Invernizzi, C.; Sada, C.; Di Noto, V.; Rizzi, G.A.; Fois, E.; Tabacchi, G.; Barreca, D. Growth of NiO thin films in the presence of water vapor: insights from experiments and theory. J. Phys. Chem. C, 1021. [Google Scholar] [CrossRef]
34. Kruve, A.; Kaupmees, K.; Liigand, J.; Oss, M.; Leito, I. Sodium adduct formation efficiency in ESI source. J. Mass Spectrom. 2013, 48, 695–702. [Google Scholar] [CrossRef] [PubMed]
35. Zhao, Y.; Truhlar, D.G. The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics, noncovalent interactions, excited states, and transition elements: two new functionals and systematic testing of four M06-class functionals and 12 other functionals. Theor. Chem. Account 2008, 120, 215–241. [Google Scholar] [CrossRef]
36. Frisch, M.J.; Trucks, G.W.; Schlegel, H.B.; Scuseria, G.E.; Robb, M.A.; Cheeseman, J.R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G.A.; et al. Gaussian 09, Revision D.02; Gaussian, Inc.: Wallingford, CT, USA, 2009. [Google Scholar]
37. Martin, J.M.L.; Sundermann, A. Correlation consistent valence basis sets for use with the Stuttgart–Dresden–Bonn relativistic effective core potentials: the atoms Ga–Kr and In–Xe. J. Chem. Phys. 2001, 114, 3408–3420. [Google Scholar] [CrossRef]
38. Dunning Jr., T. H.; Hay, P.J., Ed.; in. Modern Theoretical Chemistry; Vol. 3, pp. 1–28, Plenum: New York, 1977. [Google Scholar]
39. Reed, A.E.; Weinhold, F. Natural localized molecular orbitals. J. Chem. Phys. 1985, 83, 1736–1740. [Google Scholar] [CrossRef]
40. Bader, R.F.W. A quantum theory of molecular structure and its applications. Chem. Rev. 1991, 91, 893–928. [Google Scholar] [CrossRef]
41. Tang, W.; Sanville, E.; Henkelman, G. A grid-based Bader analysis algorithm without lattice bias. J. Phys. Condens. Matter 2009, 21, 084204. [Google Scholar] [CrossRef]