Search

Metathesis of solid GaCl 3 with NaOEt/EtOH (1:3) provided, after separation of the NaCl precipitate, a solution containing oxoalkoxide chloride complexes of gallium. Residues from evacuation of the latter were redissolved in either toluene/ MeCN (solution 1) or toluene/pyridine (solution 2). Storage of the first solution provided crystals of Ga 5 (μ 5 -O)(μ-OEt) 8 Cl 5 (1), and of the second solution - [Ga 12 (μ 4 -O)2(μ 3 -O) 5 (μ-OEt) 10 -Cl 12 Py 4 ]Py (2), both at room temperature and in relatively high yields. Compound 1 crystallizes as a vertically contracted tetragonal pyramid with the μ 5 -O ligand situated in the center of the equatorial plane defined by four trigonal bipyramidal coordinated gallium atoms. The axial Ga atom has octahedral coordination. All eight edges of the pyramid are capped by μ-OEt groups, and all the chloride ligands are situated in terminal positions. Crystals of [Ga 12 (μ 4 -O) 2 (μ 3 -O) 5 (μ-OEt) 10 Cl 12 Py 4 ]Py (2) contain two [Ga 5 (μ 4 -O) (μ 3 -O) 2 (μ-OEt) 5 -Cl 5 Py] fragments connected through a cyclic [Ga 4 (μ 3 -O) 5 -Cl 2 Py 2 ) unit with a μ 3 -O ligand in its center. Of the metal atoms, three possess tetrahedral, seven trigonal bipyramidal, and two octahedral coordination. The mass spectrum of 1 contains penta- and tetranuclear fragments. The spectrum of 2 contains heptameric fragments in addition to the pentanuclear fragments that are analogous to those in the spectrum of 1. The factors leading to formation of polymeric M(OR) n and related oligonuclear oxocomplexes are discussed.

Dissolution of BaO in 90–95% MeOH provides [Ba(OH)2(H2O)2](MeOH)2 (1) as rectangular platelet crystals. Interaction of BaO or Ba(OH)2 with 98–100% methanol results in the formation of needle shaped crystals of [Ba(OH)2(MeOH)2](MeOH) (2). The structure of 1 is composed of planar layers of tetragonally distorted [Ba(OH)4/2(H2O)4/2] cubes altered by the layers of alcohol molecules oriented in the direction perpendicular to the metal hydroxide layers. The structure of 2 is formed by layers of distorted antiprisms of Ba(μ3-ROH)(μ-OH)4(μ-ROH)2(ROH)] and [Ba(μ3-ROH)2(μ-ROH)2(μ-OH)4] composition. IR spectra of 1 and 2 are in good agreement with the observed structures. The structures of compounds 1 and 2 are compared with those of Ba(OH)2 · nH2O (n = 1, 3).

Interaction of FeX 3 , X = Cl, Br with 3 equiv. of NaOEt in toluene/ethanol media provides mixtures of iron (III) oxoethoxide, Fe 5 O(OEt) 13 , and its halide alkoxide analogs. The latter have been identified by mass-spectrometric study as Fe 5 O(OEt) 12 X and Fe 5 O(OEt) 11 X 2 . Application of FeBr 3 as a starting material leads to much more pure samples of Fe 5 O(OEt) 13 isolated with higher yields.

Prolonged storage of solutions in the Al(OPri)3–Ta(OPri)5–iPrOH system containing additional nPrOH leads to crystallization with minor yields of a new aluminium oxopropoxide, Al11O6(OPrn)10(OPri)10(OR)(ROH)2 (R=Pri, Prn) (1). Interaction of Al(OPri)3 with Mg(acac)2 (in a 1:1 ratio) in toluene on refluxing leads to formation of Al5Mg4O3(OH)3(OPri)8(acac)6 · 0.5PhMe (2) in minor yields. Both molecules contain two pentanuclear cores [M5(μ4-O)(μ3-O)(μ-OX)6(Y)4] (X=H, Prn, Y=OPri, acac/2) and differ only in the manner in which they are attached to each other, i.e. via the central [Al(μ3-O)2(μ-O)2(OR)] unit in 1, and via a common [Al–(μ3-O)] edge and an additional (μ-OH)-group in 2. The core structures in the molecules of aluminium and iron oxoalkoxides are discussed.

The electrochemical synthesis of Sc(OMe)3 (1), Sc(OEt)3 (2) and Sc5O(OPri)13 (3) was carried out via anodic oxidation of scandium metal in aliphatic alcohols. X-ray single crystal study showed 3 to be analogous to the known isopropoxides of Y, Er, Yb and In. The interaction of 3 with excess ROH (R=Me, Et, Bun, Bus, But) gives non-volatile amorphous 1, 2 and Sc(OBun)3 (4), and volatile Sc5O(OBus)13 (5) and Sc5O(OPri)8(OBut)5 (6). Oxoalkoxides Sc5O(OPri)8(OR)5 (R=Bun 7, Me 8) were obtained on reaction of 3 with n-ROH in 1:5 ratio. The mass spectral study shows 5 is an individual compound, whereas 6–8 in the gas phase consist of a number of aggregates with different extents of substitution for OPri groups, Sc5O(OR)n(OPri)13−n: for R=But n≤5, for R=Bun n≤8, and for R=Me n≤12. The maximal intensity in the spectrum of 6 is observed for Sc5O(OPri)10(OBut)2+, and in the spectra of 7 and 8 for Sc5O(OPri)12−n(OBun)n+, n=4, 5, and Sc5O(OPri)9(OMe)3+ respectively. The presence of the Sc5O(OMe)12+ ion in the spectrum of 8 indicates the possibility of replacing all the OPri in the pentanuclear core and demonstrates the existence of a ‘volatile scandium methoxide’ in the gas phase. Study of the complex formation of Sc(OR)3 with Al(OR)3 has shown that 2 and 4 form volatile Sc[Al(OR)4]3, R=Et 9, Bun 10, while 3 does not react under these conditions. Sc[Al(OPri)4]3 (11) can be obtained only on exchange reaction of ScCl3 with KAl(OPri)4. The results obtained indicate rather high stability of the [Sc5O(OR)8] core for primary and secondary R.

The colorless needle-shaped crystals of a new heterometallic 2-methoxyethoxide, BaMo2O5(OC2H4OMe)4(HOC2H4OMe) (1), have been obtained by the saturation of barium 2-methoxyethoxide solution in 2-methoxyethanol with the crystalline MoO2(OC2H4OMe)2. The precipitation started when the Ba:Mo ratio achieved a 1:2 value and the precipitate formed contained BaMoO4 as an admixture thus indicating that the formation of oxo species led partially even to formation of inorganic molybdates. Molecules of 1 involve the metal–oxygen framework quite typical of trinuclear homo- and heterometallic alkoxide species. The rather high coordination number of the barium atom (10) and the lengths of the observed interatomic distances permit to suggest that this atom in 1 forms predominantly ionic bonds and, therefore, complex 1 can be formulated as [Ba(HOC2H4OMe)]2[Mo2O5(OC2H4OMe)4]2−.

The study of the side products of the anodic dissolution of molybdenum and tungsten metals in alcohols in the presence of LiCl showed them to be [LiMo2O2(OMe)7(MeOH)] 1 in the case of MeOH and [LiMo2O4(OEt)5(EtOH)] 2 in EtOH. Treatment of 2 with an excess of PriOH gave [LiMo2O4(OPri)5(PriOH)] 3, the structure of which was confirmed by a study of [{LiMo2O4(OPri)4(OC2H4OMe)}2] 4, the product of partial substitution of OR groups in 3 by 2-methoxyethoxide ligands. Reaction of 2 with an excess of MeOC2H4OH led to an equimolar mixture of [MoO2(OC2H4OMe)2] and [LiMoO2(OC2H4OMe)3] 5. In PriOH a crystalline product identified as [Mo6O10(OPri)12] 6 was isolated. Anodic oxidation of tungsten in MeOH gave a mixture of homometallic W(OMe)6 and [WO(OMe)4]. Electrosynthesis in EtOH gave as major product an amorphous glass-like mass {after separation of crystalline [WO(OEt)4] by filtration and subsequent drying of the filtrate in vacuo}. Treatment of the latter with an excess of HOC2H4OMe led to crystallization of [{LiWO2(OC2H4OMe)3}2· 2Li(HOC2H4OMe)2]2+[W6O19]2– 7. Complexes 1, 4 and 7 were characterized by X-ray single-crystal studies. A GLC-mass spectrometric study of the composition of organic side products indicated that the processes were associated with formation of ethers, alkyl halides, aldehydes or ketones and their derivatives. The nature of the possible side reactions was deduced on the basis of the data obtained.

The reaction of lanthanum isopropoxide with the isopropoxide of molybdenum(VI), MoO(OPr i ) 4 , in 1:2 molar ratio in hexane, leads to the formation of the mixed-metal hexanuclear complex La 2 Mo 4 O 4 ( μ 4 -O) 4 ( μ -OPr i ) 8 (OPr i ) 6 ( 1 ), formally derived from the dioxomolybdenum species MoO 2 (OPr i ) 2 . The molecule of 1 contains an unusual tetragonal bipyramidal La 2 Mo 4 metal core supported by four tetradentate oxobridging ligands binding two neighbouring molybdenum and both lanthanum atoms each. Complex 1 readily decomposes either in solution in iso-propanol or on heating in vacuo to 90°C. The mechanism of the latter process is discussed.

The crystalline Li2(WO)2(OMe)10·MeOH (I) is formed as a side product in the process of anodic oxidation of tungsten in methanol in the presence of LiCl, which is used as a conductive additive. The structure of I as determined by the X-ray diffraction (XRD) method features infinite chains made up of two alternating tetranuclear species [Li2(WO)2(OMe)10] (A) and [Li2(WO)2(OMe)10(MeOH)2] (B), linked via LiOW bridges involving the Li atom belonging to fragment A and tungstenyl group from fragment B. Each fragment occupies a special position in the crystallographic inversion center and has a metal–oxygen framework. All tungsten atoms have octahedral coordination, whereas all lithium vertices have five-coordinated trigonal bipyramidal environments. The H-bonds of the (A)WO…HOMe(B) type in the crystal of I provide the links between the A and B fragments belonging to the different chains.

MoO(OMe) 4 has been prepared by anodic oxidation of molybdenum metal in anhydrous methanol containing LiCl as an electrolyte. The X-ray single crystal study showed the complex to consist of pseudo-centrosymmetric dimeric molecules, [MoO(OMe) 3 (μ-OMe)] 2 . The general effect of the M(μ-OR) 2 M ring upon the arrangement of bonds with increased multiplicity is discussed in this and related molecules.

The review surveys the pathways of formation of crystalline oligomeric oxoalkoxides M mO n(OR) p, which are products of partially controlled (or uncontrolled) hydrolysis, oxidation, thermal decomposition of mono- and bimetallic alkoxides of the ortho series M(OR) n and M mM 'n(OR) p or elimination of ethers from these compounds. The physicochemical properties of oxoalkoxides (solubility, the behaviour in solutions, volatility, etc.) differ considerably from the properties of the corresponding alkoxides. Hence, oxoalkoxides can be considered as immediate precursors of oxide materials produced by sol–gel technology. The M mO n(OR) p compounds are classified according to the sizes of associates. The crystal chemistry of alkoxides is discussed. The bibliography includes 249 references.

The hexanuclear complex of calcium oxo ethoxide ethanol solvate, [Ca6O2(OEt)8]·14EtOH 1 has been isolated after the prolonged refluxing of an ethanol solution of calcium ethoxide in the presence of the oxygen in air and studied by X-ray diffraction; the metal-oxygen framework is built of two [Ca4O4] cubes sharing a common [Ca2O2] face, which involves both oxo groups.

Reaction of MoO(OEt)4 with an excess of methoxyethanol leads to the formation of MoO(OC2H4OMe)4, which decomposes to give complex MoO2(OC2H4OMe)2 1, an X-ray structural study of which shows that its crystals are constructed of monomeric molecules with both methoxyethoxide groups forming chelate rings around the molybdenum atoms; interaction of 1 with NaOC2H4OMe in methoxyethanol results in the formation of a complex NaMoO2(OC2H4OMe)3 2, whose polymeric structure, established by X-ray analysis, contains a planar tetranuclear fragment analoguous to that found in Ti4(OMe)16.

The solvate LiOMe·2MeOH (1) was isolated from a solution of LiOMe in MeOH, its tetrameric unit [Li4(μ-OR)4(μ-ROH)2(ROH)4]·2ROH may be described as two distorted squares [Li2(μ-OR)(μ-ROH)], linked by bridging alkoxy groups and two hydrogen bonds; 1 easily loses the solvate alcohol yielding polymeric LiOMe.

The X-ray single-crystal studies of [M{Ti2(OR)9}2](M = Ca, Ba; R = Et) obtained from EtOH solutions in 1 : 4 metal–titanium ratios show that these complexes, both in the solid state and in solution, are composed of symmetric molecules, in which the central eight-coordinated metal atom is bound to two face-sharing bioctahedral [Ti2(OR)9] groups.

An X-ray structural study of the crystals isolated from the solutions obtained by the reaction of Ba metal with Ti(OPri)4 in isopropyl alcohol has been carried out; the crystals of the compound, which is a precursor for the synthesis of BaTiO3, contain molecules of two different kinds [Ba4Ti4O4(OR)16(ROH)4] and [Ba4Ti4O4(OR)16(ROH)3], where R = Pri.

CONTENTS I. Classification of the alcohol derivatives of the elements 161 II. Alkoxides of the alkali and alkaline earth metals, magnesium, and thallium(I) 162 III. Phenoxides of the alkali and alkaline earth metals, magnesium, and thallium(I) 177