On chalcogenide halogenides of rhenium:: Synthesis and crystal structures of the triangular clusters Re3E7X7 (E = S, Se; X = Cl, Br)

The compounds Re3E7X7 are obtained from rhenium tetrahalides ReX4, elemental chalcogens and the respective chalcogen halides E2X2 or SeX4 (E = S, Se; X = Cl, Br). Re3S7Cl7, Re3S7Br7 and Re3Se7Br7 are formed in solutions of sulfur or selenium halides or SiBr4 in form of black crystals and crystallize isotypically in the trigonal space group P31c. Re3Se7Cl7 is formed by solid state reaction of ReCl4, Se and SeCl4 or by thermal decomposition of Se-4[ReCl6], crystallizing as red, in thin layers transparent crystals in the orthorhombic space group Pbcm. The crystal structures consist of discrete positively charged cluster units and halide ions according to the formula [Re-3(mu(3)-E)(mu(2)-E-2)(3)X-6]X-+(-). In the rhenium triangular clusters the Re-Re distances range from 269,0 to 270,4 pm for the sulfur and from 273,3 to 275,3 pm fur the selenium containing compounds. The Re-3 units are capped by chalcogen atoms, three E-2 groups form bridges over the edges of the Re-3 triangles. The trigonal and the orthorhomhic structure type show differences in the site symmetry of the clusters (C-3 vs. C-5) and in the stacking sequence of the molecules, which are packed in the motif of a closest packing of spheres.