SYNTHESIS, STRUCTURE AND PROPERTIES OF THE CLUSTER ANIONS [(MO6CL8(I))X6(A)](2-) WITH XA-EQUIVALENT-TO-F, CL, BR, I

The tetrabutylammonium (TBA) salts of the octa-mu-3-Chloro-hexahalogeno-octahedro-hexamolybdate (2-) ions [(Mo6Cl8i)X6a;]2- with X(a) = (BF4)-, Cl-, Br-, I- and the appropriate free acid of the type H-2[(Mo6Cl8i)X6a] with X(a)=(BF4)-, Cl-, Br-, I- and the corresponding TBA halide. The crystal structures determined from single crystals show systematic changes in bond distances and angles with the F(a) --> I(a) ligand exchange (increasing Mo6 octahedron; slight compression of the Cl8i cube). Infrared and Raman spectra were measured in solution and in the solid state (80 K). The vibrational modes of the cluster kernel Mo6Cl8i are approximately site constant, but all vibrations with contributions of the X(a) ligands show characteristic shifts. The most important bands are assigned by use of normal coordinate analyses.