Titania samples prepared by different non-hydrolytic sol–gel methods, mainly based on the etherolysis and alcoholysis of titanium tetrachloride, have been found to differ in both structure and texture. Thus, the reaction of diethyl ether with TiCl4 at 110 °C affords anatase, which begins to convert into rutile only around 1000 °C. The reaction of TiCl4 with ethanol leads to rutile as early as 110 °C, whereas the reaction of tert-butyl alcohol at 110 °C leads to the singular formation of brookite.

Preparation of anatase, brookite and rutile at low temperature by non-hydrolytic sol–gel methods

Publisher Summary This chapter discusses the transition-metal alkoxides. Primary alkoxides of chromium (III) do not appear to undergo alcoholysis reactions, even under forcing conditions with other alcohols. This is rather unusual in view of the usually strong lability of the alkoxy groups exhibited in alkoxides of most of the metals studied; the main factor hindering such facile interchange has generally been explained on the basis of steric requirements. The general inertness of the primary alkoxides of chromium (III), a more detailed investigation of their substitution reactions has been carried out, and it has been shown that although these are inert to other simple alcohols they undergo interchange with chelating ligands such as ethanolamine, β-diketones and carboxylic acids.

Transition-Metal Alkoxides

Alkoxides and alkylalkoxides of metals and metalloids

Metal oxide nanoparticles can be fabricated under high control via nonaqueous sol–gel synthesis. This route has been shown to lead to highly crystalline, uniform nanostructures, which explains the high and growing interest it is receiving. The underlying mechanisms are, however, so far only rudimentarily understood on a molecular scale. Here, we applied in situ FTIR spectroscopy and other techniques to monitor the nonaqueous synthesis of titania nanoparticles that can be easily stabilised in polar solvents and thus, possess high potential for application. A special focus is put on the kinetics of the organic condensation mechanisms enabling the reaction of the precursor to the inorganic nanoparticles. By comparing these kinetics to the process of nanoparticle formation monitored via complementary methods such as TEM and dynamic light scattering, a detailed insight into the principles and mechanisms of nanoparticle formation via the nonaqueous sol–gel synthesis is achieved.

In situ investigation of molecular kinetics and particle formation of water-dispersible titania nanocrystals

The reactions of TiCl4 and Ti(OiPr)Cl3 with 1−3 molar equiv of 2-propanol give the dimeric complexes [TiCl3(HOiPr)(μ-Cl)]2 (1), [TiCl2(OiPr)(HOiPr)(μ-Cl)]2 (2), and [TiCl2(OiPr)(HOiPr)(μ-OiPr)]2 (3). The reactions are shown to proceed stepwise with the consecutive addition of 2-propanol. Complexes 2 and 3 are dynamic in solution. However, the proton VT NMR studies show that they are static and remain the dimeric features in solution at low temperatures. Two inequivalent methyl environments are observed for the 2-propanol ligand of complex 3, probably due to the intramolecular hydrogen bonding from the isopropanolic hydrogen to the chloride on the second titanium metal center. 2 crystallizes in the orthorhombic space group Pbca with cell parameters of a = 12.605(3) A, b = 12.841(4) A, c = 15.414(4) A, Z = 4, Dcalcd = 1.456 g/cm3, R = 0.049, Rw = 0.062, and GOF = 1.38. 3 crystallizes in the monoclinic space group P21/c with cell parameters of a = 9.457(2) A, b = 15.277(2) A, c = 11.354(4), β = 112.76(2)°, Z...

Stepwise Reactions of TiCl4 and Ti(OiPr)Cl3 with 2-Propanol. Variable-Temperature NMR Studies and Crystal Structures of [TiCl2(OiPr)(HOiPr)(μ-Cl)]2 and [TiCl2(OiPr)(HOiPr)(μ-OiPr)]2

J. S. Jennings

Papers

146. Some esters of titanium