METAL-SELENOLATE CHEMISTRY - STEREOCHEMISTRY OF ADAMANTANE-TYPE CLUSTERS OF FORMULA [(MU-SEPH)6(MSEPH)4]2- (M = ZN AND CD)

The structures of three tetramethylammonium salts containing anions of formula [(mu-SePh)6(MSePh)4]2- (M = Zn and Cd) were determined by single crystal X-ray diffraction techniques. The Zn salt crystallizes in different space groups depending upon the solvent combination used in the synthesis. Thus crystals of (Me4N)2[Zn4(SePh)10], 1, grown from a mixture of methanol, acetonitrile, and acetone are triclinic, space group P1BAR, with cell dimensions a = 13.214(2), b = 23.859(2), c = 13.072(1) angstrom, alpha = 91.134(8), beta = 113.350(8), gamma = 79.865(9)-degrees, and Z = 2. In the absence of acetone, a solvated crystal (Me4N)2[Zn4(SePh)10] - CH3CN, 2, is formed, which belongs to did monoclinic space group P2(1)/n with a = 14.248(1), b = 39.722(2), c = 13.408(1) angstrom, beta = 97.132(5)-degrees, and Z = 4. The Cd salt (Me4N)2[Cd4(SePh)]10], 3, crystallizes in the monoclinic space group P2(1)/c, with a = 20.830(2), b = 14.282(l), c = 25.872(1) angstrom, beta = 99.626(6)-degrees, and Z = 4. These three salts are the first examples of homoleptic, tetranuclear selenolatometal(II) anions with (mu-Se)6M4 cages of adamantane-type stereochemistry. In each case the phenyl substituents of the bridging ligands adopt the configuration [aae, aae, aee, aee], which has the minimum number of two 1,3-axial-axial non-bonding substituent interactions.