Synthesis, structure and properties of the polychalcogenides [M₄Te₁₂]^4- (M=Cd, Hg)

The cluster anions, [M₄Te₁₂]^4- (MCd, Hg) are reported. (Et₄N)₄[Cd₄Te₁₂] (I) was prepared by the reaction of CdI₂, K₂Te₂ and Et₄NBr in a 2:3:2 molar ratio, in DMF. I crystallizes in the orthorhombic space group Cmca (No. 64) with a = 15.482(5), b = 22.563(4), c = 18.027(4) Å, V = 6297(5) ų and Z = 4. The black rectangular platelet crystals of (Me₄N)₄[Hg₄Te₁₂] (II) were obtained from the reaction of HgCl₂ and K₂Te in a 2:5 molar ratio in DMF. II crystallizes in the monoclinic space group P2₁/n (No. 14) with a = 10.324(3), b = 21.851(6), c = 11.125(4) Å, β = 110.63(3)°, V = 2348(3) ų and Z = 2. [M₄Te₁₂]^4- is a cluster with two Te^2-, two Te₂^2- and two Te₃^2- ligands connecting a planar array of four tetrahedral M²⁺ metal centers. Its shape may be described as a basket, consisting of an {M₄(Te₂)₂Te₂} core with two side Te₃^2- handles. The average M-Te and Te-Te distances are 2.85(8) and 2.74(2) Å for I, respectively, and 2.86(12) and 2.73(1) Å for II, respectively. The far-IR spectra show two absorptions at 173 and 160 cm^-1 for I and at 167 and 148 cm^-1 for II. Thermal gravimetric analysis data are reported.