N. I. Kozlova

Bio: N. I. Kozlova is an academic researcher from Moscow State University. The author has contributed to research in topics: Alkoxide & X-ray crystallography. The author has an hindex of 4, co-authored 8 publications receiving 84 citations. Previous affiliations of N. I. Kozlova include Russian Academy of Sciences.

The alkoxides of zirconium and hafnium: direct electrochemical synthesis and mass-spectral study. Do “M(OR)4”, where M=Zr, Hf, Sn, really exist?

Abstract: The direct electrochemical synthesis of zirconium (1a) and hafnium (1b) alkoxides, M(OPri)4·PriOH, Zr(OBui)4·BuiOH (4a) and M(OR)4, where R=Et (2a,b), Bun (3a), Bus (5a), C2H4OMe (6a,b) has been carried out by anodic oxidation of metals in anhydrous alcohols in the presence of LiCl as a conductive additive to give quantitative yields. The solubility polytherms and dissociation pressure of1a,b have been investigated. It has been proved by means of chemical analysis, X-ray powder, and IR spectral studies that the desolvation of 1a,b and Sn(OPri)4·PriOH (1c) is accompanied by the formation of amorphous oxocompounds M3O(OPri)10. On the basis of1H NMR data it has been proved that the structure of the latter is analogous to that of known triangular cluster molecules M3(μ3-O)(μ3-OR)(μ-OR)3(OR)6, where M=Mo, W, U. Mass-spectral data and the determined physicochemical characteristics of1–5 permit to conclude that the samples of composition M(OR)4, where M=Zr, Hf, and2,3,5 contain tri- and tetranuclear oxocomplexes M3O(OR)10 and M4O(OR)14 respectively, along with Zr(OR)4 oligomers of different molecular complexity.

Direct electrochemical synthesis of metal alcoholates

Abstract: 1. The authors have studied the conditions for electrochemical synthesis of the alcoholates of Ga, Sc, Y, Ge, Ti, Zr, Nb, and Ta with anodic dissolution of the metals in absolute alcohols in the presence of a base electrolyte. The optimal base electrolytes are the salts R4NBr and R4NBF4. The limits of applicability of this synthesis method are determined when various metals are used as the anode. 2. It is postulated that the primary products of anodic oxidation of the metals are alkoxyhalides, the nature of which governs the further direction of the electrode process.

Studies on Mixed β-Diketonate/Isopropoxide Compounds of Zirconium and Hafnium, the X-ray Single-Crystal Structures of [M2(OPri)6(tmhd)2] (M = Zr, Hf): Some Chemistry Important in the MOCVD of Oxides

Abstract: Reactions of the homoleptic alkoxides [M(OPri)4·(PriOH)] (M = Zr or Hf) with different stoichiometric amounts of the β-diketone ligand tmhd-H (2,2,6,6-tetramethylheptane-3,5-dione) have been investigated. Crystalline, but powdery, materials with a stoichiometry close to [M(OPri)2(tmhd)2] have been isolated by reacting 2 mol of the β-diketone with 1 mol of the metal alkoxide; we present a full explanation based on the 1H NMR results for their behavior in solution. The compounds [M2(OPri)6(tmhd)2] [M = Zr (1b), and Hf (2b)] have been obtained from the exhaustive recrystallization of the above reaction mixture or as the products of the 3:1 stoichiometric reaction between [M(OPri)4.(PriOH)]2 and tmhd-H. Compounds 1b and 2b have been shown by X-ray crystallography to be isomorphous and are useful precursors for the deposition of the metal oxides by methods such as liquid injection CVD. The symmetrical, dimeric structure of the compounds, with one β-diketonate attached to each half of the dimer, may explain why...

Chemistry of 2,2,6,6,-tetramethyl-3,5-heptanedione (Hthd) modification of zirconium and hafnium propoxide precursors.

Abstract: The modification of different zirconium propoxide and hafnium propoxide precursors with 2,2,6,6,-tetramethyl-3,5-heptanedione (Hthd) was investigated by characterization of the isolated modified species. The complexes [Zr(OnPr)3(thd)]2, [Zr(OnPr)(OiPr)2(thd)]2, Zr(OiPr)(thd)3, [Hf(OnPr)3(thd)]2, and Hf(OiPr)(thd)3 were isolated and characterized. The structure of the n-propoxide analogue of Zr(OiPr)(thd)3 could not be refined, but its existence was clearly demonstrated by XRD and 1H NMR. The modification of the propoxide precursors involves mono- and trisubstituted intermediate compounds and does not involve a disubstituted compound; thus, the commercial product that is claimed to be “Zr(OiPr)2(thd)2” and is most commonly used for the MOCVD preparation of ZrO2 does not exist. No evidence was found for the presence of such a compound in either zirconium- or hafnium-based systems. Formation of the dimeric hydroxo-di-thd-substituted complex, [Hf(OH)(OiPr)(thd)2]2, which could be isolated only for hafnium-based systems, occurs on microhydrolysis. All heteroleptic intermediates are eventually transformed to the thermodynamically stable Zr(thd)4 or Hf(thd)4. The compounds obtained from isopropoxide precursors showed a higher stability than those with n-propoxide ligands or a combination of both types. In addition, it is important to note that residual alcohol facilitates the transformation and strongly enhances its rate. The unusually low solubility and volatility of MIV(thd)4 has been shown to be due to close packing and strong van der Waals interactions in the crystal structures of these compounds.

Atomic layer deposition of ZrO2 thin films using a new alkoxide precursor

Abstract: Zirconium oxide thin films were grown by atomic layer deposition using a new type of Zr alkoxide: [Zr(O t Bu) 2 (dmae) 2 ] 2 (dmae is dimethylaminoethoxide). Water was used as the oxygen source. The films grown at 190–240 °C were amorphous, and the films grown at 290–340 °C were nanocrystalline. The highest refractive index of the films was 2.08 at a wavelength of 580 nm. The permittivity of a film grown at 240 °C was 25.