SEXIDENTATE COORDINATION OF THE PENDANT-ARM MACROCYCLE 6,13-DIMETHYL-1,4,8,11-TETRAAZACYCLOTETRADECANE-6,13-DIAMINE (L1) TO ZINC(II) - CRYSTAL-STRUCTURE OF [ZNL1][CLO4]2.H2O

The pendant-arm macrocycle 6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine (L1) co-ordinates as a sexidentate ligand to zinc(II) in neutral aqueous solution. The complex [ZnL1]-[ClO4]2.H2O crystallises in the monoclinic space group P2(1)/c, a = 9.488(4), b = 14.736(9), c = 16.037(4) angstrom, beta = 97.95(3)-degrees and Z = 4. The Zn-N bond lengths in [ZnL1]2+ are, on average, the shortest known for a hexaaminezinc(II) complex. The stability constant for formation of [ZnL1]2+ was determined to be log K 15.0 +/- 0.1, from potentiometric titrations. Five of the six successive protonation constants for the hexaamine L1 were measured similarly and values pK(a) 2.9, 5.5, 6.3, 9.9 and 11.0 found.