412. Structural chemistry of the alkoxides. Part IV. Normal alkoxides of silicon, titanium, and zirconium

Abstract

The normal alkoxides, Ti(OC,H,,+,), where n = 2, 3, 4, 5, 6, 7, and 8, and Zr(OC,H,,+,), where n = 2, 3, 4, 5, 6, and 8, have been prepared and their molecular weights and boiling points measured. Molecular complexity is practically independent of chain length while boiling points increase linearly with molecular weight. Structures for the complex alkoxides are discussed. Vapour pressures and vapour densities were measured for zirconium tetraethoxide and tetraisopropoxide and it is suggested that the vaporisation process is [Zr(OR)J, (liquid) + nZr(OR), (vapour), and that the energy of intermolecular attraction is ca. 18 kcals./mole. Entropies of vaporisation for the n-alkoxides of silicon and titanium increase with chain length, and this behaviour is discussed in terms of molecular " entanglement " in the liquid state.

Full spectroscopic characterization of an hydrolytically stable and colored Ti(IV)-precursor in solution

“…16 be applied to the equilibrium (3/4) [Ti 4 (OEt) 16 ] <-> [Ti 3 (OEt) 12 ] showing that this entropy-driven depolymerization (DS = +94-95 J.mol À1 .K À1 ) should be an endothermic process characterized by DH = +92 kJ.mol À1 for transformation of the tetramer into the 565-trimer against DH = +2350 kJ.mol À1 for transformation into the 555-trimer. Considering that four ethoxy bridges are broken on going from the tetramer towards the 565-trimer, the enthalpy content of a Ti-OEt-Ti bridge may be estimated as ÀDH/4 = À23 kJ.mol À1 in good agreement with the value À21 kJ.mol À1 derived from latent heat vaporization measurements [72] or the value À23 kJ.mol À1 derived from 1 H NMR data [73]. The same value derived from the 555-isomer being in complete disagreement with available experimental data, the existence of this structure in solution may be ruled out beyond any doubt on thermodynamic grounds.…”

Anionic coordinated polymerization ofɛ-caprolactone with aluminium, zirconium and some rare earths alkoxides as initiators in the presence of alcohols

“…Concerning the structure of these compounds, multinuclear aggregates have been reported in which zirconium has usually a coordination number of six 38,39) . Bulky ligands such as tert-butoxy are required to stabilize the monomeric species.…”

“…Bulky ligands such as tert-butoxy are required to stabilize the monomeric species. In 2-propanol, zirconium isopropoxide is dimeric 38) of general formula Zr 2 (OiPr) 8 (iPrOH) 2 , with an edgeshared octahedral structure due to hydrogen bonding 40) (Scheme 4). It may be assumed that adding alcohol could break the former aggregates because new ROH e Zr bonds would replace the ROZr e Zr bonds to give dimers.…”

Structural role of polyethylene glycol in the formation of anatase nanocrystalline titania at low temperature

“…Ti(O n Bu) 4 can have a trimeric [22,23] or dimeric [24,25] structure, as shown below: 4 and Ti(O t Am) 4 was studied by Nabavi et al [26] for which NMR signals were easily observed, whereas no signal was detected for Ti(O n Bu) 4 . However, the authors extrapolated their conclusions to all titanium alkoxide/alcohol systems.…”