The synthesis of tellurometalates by the reduction of binary telluride melts with potassium in liquid ammonia

Abstract

The reduction of binary telluride melts with potassium in liquid ammonia in the presence of 18-Crown-6 or 2,2,2-Crypt has been employed to synthesize and precipitate tellurometalates. The method is more rapid than conventional extraction techniques and, since lower temperatures are involved, potentially unstable fragments are conserved. A melt of nominal composition CdTe3 dissolved with K and 18-Crown-6 in liquid NH3 affords [K(18-Crown-6)]4[Cd4Te12] (1) after recrystallization from CH3CN–Et2O. Compound 1 crystallizes in the triclinic space group [Formula: see text] with one formula unit in a cell of dimensions a = 12.673(1) Å, b = 13.694(3) Å, c = 14.483(3) Å, α = 117.54(2)°, β = 96.43(1)°, and γ = 100.00(1)° at 113 K. Full anisotropic refinement of the structure on Fo2 led to a value of R1 = 0.026 for those 6654 reflections having Fo2 > 2σ(Fo2). The [Cd4Te12]4− anion of 1, which may be formulated as [Cd4(Te)2(Te2)2(Te3)2]4−, consists of a rectangular array of four Cd2+ centers linked by Te2−, Te2−, and Te32− ligands. As expected from the solid-state structure, the 125Te NMR spectrum of 1 in CD3CN shows four resonances at −11, −259, −548, and −1682 ppm. A melt of nominal composition PbTe2 was dissolved with K and 2,2,2-Crypt in liquid NH3 to afford [K(2,2,2-Crypt)]2[Pb2Te3]•CH3CN (2) after recrystallization from CH3CN. Compound 2 crystallizes in the triclinic space group CI1−P1 with one formula unit in a cell of dimensions a = 11.105(3) Å, b = 11.748(4) Å, c = 11.922(3) Å, α = 118.78(2)°, β = 96.52(2)°, and γ = 91.03(3)° at 113 K. Full anisotropic refinement of the structure on Fo2 led to a value of R1 of 0.074 for those 11 135 reflections having Fo2 > 2σ(Fo2). The anion of 2 consists of a triangle of Te2− ligands capped above and below the plane by two Pb2+ centers to define a trigonal bipyramid. The 125Te NMR spectrum of 2 in CD3CN shows one resonance at −928 ppm (JPb–Te: 1090 Hz). Keywords: tellurometalates, liquid ammonia, synthesis, crystal structure.