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 °C, followed by crystallization at −20 °C, afforded
(TiCl4)2(Se2(CH3)2)
(78%) and
(TiCl4)2(Se2(CH2CH3)2)
(63%), respectively, as red and orange crystalline solids.
(TiCl4)2(Se2(CH2CH3)2)
is stable in solution and in the
solid state at 23 °C, but
(TiCl4)2(Se2(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 °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
TiCl4(Se(CH2CH3)2)2
(96%), respectively.
X-ray crystal structures of
(TiCl4)2(Se2(CH2CH3)2),
TiCl4(Se(CH3)2)2, and
TiCl4(Se(CH2CH3)2)2
were determined
to establish solid state nuclearities.
(TiCl4)2(Se2(CH2CH3)2)
crystallizes in the hexagonal space group
P3121
with a = 12.106(1) Å, c =
10.786(1) Å, V = 1368.8(4) Å3, and
Z = 3.
TiCl4(Se(CH3)2)2
crystallizes in the
monoclinic space group P21/n with
a = 8.175(1) Å, b = 13.051(1) Å,
c = 16.871(3) Å, β = 102.675(8)°,
V =
1756.3(2) Å3, and Z = 4.
TiCl4(Se(CH2CH3)2)2
crystallizes in the monoclinic space group
P21/n with a
=
6.404(4) Å, b = 16.376(7) Å, c =
13.058(8) Å, β = 101.45(4)°, V =
1342(1) Å3, 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 °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.