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Low temperature methods have been applied to the synthesis of many advanced materials. Non-hydrolytic sol-gel (NHSG) processes offer an elegant route to stable and metastable phases at low temperatures. Excellent atomic level homogeneity gives access to polymorphs that are difficult or impossible to obtain by other methods. The NHSG approach is most commonly applied to the preparation of metal oxides, but can be easily extended to metal sulfides. Exploration of experimental variables allows control over product stoichiometry and crystal structure. This paper reviews the application of NHSG chemistry to the synthesis of negative thermal expansion oxides and selected metal sulfides.

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A series of five ortho-lithiated imines (Li-L(n); n = 1-5) was synthesized via the reaction of an aryl or alkyl acetophenone imine with n-butyllithium. The ortho-lithiated imines were subsequently reacted with Ti(NR)Cl(2)py(3) (R = C(CH(3))(3), 2,6-Me(2)C(6)H(3), 2,6-Et(2)C(6)H(3), or 2,6-(i)Pr(2)C(6)H(3)), yielding complexes of the form (L(n))(2)Ti(NR). Several of the resulting complexes [(L(1))(2)Ti(NC(CH(3))(3)), 1a; (L(3))(2)Ti(N-2,6-Me(2)C(6)H(3)), 3b; and (L(5))(2)Ti(NC(CH(3))(3)), 5a] were structurally characterized using small molecule X-ray diffraction. The C(2) symmetric complexes produced in these reactions displayed a distorted square pyramidal geometry. In each complex the titanium center was located above the square plane of the two coordinated bidentate ligands and the chelating C approximately N ligands were folded away from the metal center. When a less sterically demanding alkylimine was used (L(4)), the resulting complex was isolated as an equilibrium mixture of cis and trans isomers of the empirical formula (L(4))(2)Ti(NC(CH(3))(3))py (cis/trans 4a).