Adducts of titanium tetrachloride with alkylselenium compounds: Molecular precursors to titanium diselenide films

Treatment of titanium tetrachloride (2 equiv) with dimethyl diselenide or diethyl diselenide (1 equiv) in hexane at 0 degrees C, followed by crystallization at -20 degrees C, afforded (TiC4)(2)(Se-2(CH3)(2)) (78%) and (TiCl4)(2)(Se-2(CH2CH3)(2)) (63%), respectively, as red and orange crystalline solids. (TiCl4)(2)(Se-2(CH2CH3)(2)) is stable in solution and in the solid state at 23 degrees C, but (TiCl4)(2)(Se-2(CH3)(2)) decomposes to TiCl4(Se(CH3)(2))(2), gray selenium, and other products upon standing in hexane solution, in the solid state, or upon sublimation at 250 degrees C. Treatment of titanium tetrachloride with 2 equiv of dimethyl selenide or diethyl selenide in hexane at ambient temperature afforded a spectroscopically pure brick red solid of TiCl4(Se(CH3)(2))(2) (96%) or TiC4(Se(CH2CH3)(2))(2) (96%), respectively. X-ray crystal structures of (TiC4)(2)(Se-2(CH2CH3)(2)), TiCl4(Se(CH3)(2))(2), and TiCl4(Se(CH2CH3)(2))(2) were determined to establish solid state nuclearities. (TiCl4)(2)(Se-2(CH2CH3)(2)) crystallizes in the hexagonal space group P3(1)21 with a = 12.106(1) Angstrom, c = 10.786(1) Angstrom, V = 1368.8(4) Angstrom(3), and Z = 3. TiCl4(Se(CH3)(2))(2) crystallizes in the monoclinic space group P2(1)/n with a = 8.175(1) Angstrom, b = 13.051(1) Angstrom, c = 16.871(3) Angstrom, beta = 102.675(8)degrees, V = 1756.3(2) Angstrom(3), and Z = 4. TiCl4(Se(CH2CH3)(2))(2) crystallizes in the monoclinic space group P2(1)/n with a 6.404(4) Angstrom, b = 16.376(7) Angstrom, c = 13.058(8) Angstrom, beta = 101.45(4)degrees, V = 1342(1) Angstrom(3), and Z = 4. TiCl4(Se(CH3)(2))(2) and TiCl4(Se(CH2CH3)(2))(2) were evaluated as precursors to titanium diselenide films. TiCl4(Se(CH3)(2))(2) was not a good precursor, but TiCl4(Se(CH2CH3)(2))(2) afforded rose-bronze colored titanium diselenide films at substrate temperatures of 500-600 degrees C. The films were characterized by X-ray powder diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. Surprisingly, titanium diselenide films prepared from TiCl4(Se(CH2CH3)(2))(2) are moisture sensitive and are apparently hydrolyzed by ambient moisture to titanium dioxide and hydrogen selenide. The relevance of the coordination chemistry to the development of precursors to titanium diselenide films is discussed.