PREPARATION, VIBRATIONAL-SPECTRA, NORMAL- COORDINATE ANALYSIS, AND CRYSTAL-STRUCTURE OF FAC-(PPN)2[RECLBR2I3]

By treatment of cis-[ReBr2I4]2- with HCl fac-[ReClBr2I3]2- is formed b eside other mixed complex ions of the Type [ReCl(k)Br(l)I(m)]2-, k + l + m = 6, which have been separated by ion exchange chromatography on diethylaminoethyl cellulose. The X-ray structure determination on sing le crystals of (PPN)2[ReClBr2I3] (monoclinic, space group P2(1)/c, a = 22.059(3), b = 13.569(2), c = 23.9679(2) angstrom, beta = 106.194(4)- degrees, Z = 4) reveals the complete ordering of the complex anions. D ue to the different trans influence the bond lengths ReCl (2.39) and R eBr (2.50) are slightly increased, the average ReI distance (2.66 angs trom) is a little shortened as compared with corresponding homoleptic octahedral complexes. The well resolved low temperature (80 K) IR and Raman spectra exhibit rhenium-halogen stretching vibrations in charact eristic regions. The assignment is confirmed by the normal coordinate analysis based on a general valence force field. Taking into account i ncrements of the trans influence on the valence force constants of the structural groups an adjustment between calculated and observed frequ encies within a few cm-1 is achieved.