QUATERNARY CHLORIDES AND BROMIDES WITH INTERSTITIALLY STABILIZED DOUBLE OCTAHEDRA, A(2)[GD-10(C-2)(2)]CL-19 (A=RB, CS), A(2)[GD-10(C-2)(2)]BR-19 (A=K, RB), RB-2[TB-10(C-2)(2)]BR-19, AND K-2[GD-10(C-2)(2)]BR-20

The new quaternary chlorides and bromides, A(2)[Gd-10(C-2)(2)]Cl-19 (A =Rb,Cs), A(2)[Gd-10(C-2)(2)]Br-19 (A=K,Rb), Rb-2[Tb-10(C-2)(2)]Br-19, and K-2[Gd-10(C-2)(2)]Br-20, have been synthesized in sealed niobium c ontainers as single crystals through reduction of the respective rare- earth halide with rare-earth or alkali metal in the presence of alkali halide and hexahalobenzene as the carbon source. The structure determ inations for CS2[Gd-10(C-2)(2)]Cl-19 (as a representative for this cla ss of compounds) and K-2[Gd-10(C-2)(2)]Br-20 are reported in detail. T he connection patterns of the basic [Gd-10(C-2)(2)]X(18)(i)X(8)(a) uni ts are as as essentially ionic with strong gadolinium-carbon covalent bonding inside the [Gd-10(C-2)(2)] clusters and with one and zero exce ss electrons, respectively.