MONONUCLEAR AND DINUCLEAR ZINC(II) COMPLEXES OF BIOLOGICAL RELEVANCE - CRYSTAL-STRUCTURES OF [L2ZN](PF6)2, [L'ZN(O2CPH)2(H2O)], [L'2ZN2(MU-OH)2](CLO4)2, AND [L'2ZN2(MU-OH)(MU-CH3CO2)2](CLO4)BULLET-H2O (L = 1,4,7-TRIAZACYCLONONANE, L' = 1,4,7-TRIMETHYL-1,4,7-TRIAZACYCLONONANE)

The macrocycle 1,4,7-triazacyclononane (C6H15N3;L) reacts with Zn(II) ions in methanolic solution forming the 2:1 species [L2Zn]2+. The crystal structure of [L2Zn](PF6)2 (1) has been determined. Crystal data: space group C2/c, a = 9.719 (2) angstrom, b = 16.312 (3) angstrom, c = 15.017 (3) angstrom, beta = 92.04 (3)-degrees, V = 2379.3 (8) angstrom 3, and Z = 4. The zinc ions are in a distorted octahedral environment of six amine nitrogen donor atoms. In contrast, the sterically more demanding tridentate macrocycle 1,4,7-trimethyl-1,4,7-triazacyclononane (C9H21N3;L') forms 1:1 species containing the L'Zn fragment. In the presence of sodium benzoate the mononuclear species [L'Zn(O2CPh)2(H2O)] (2) is generated. Crystal data: space group P1BAR, a = 8.193 (2) angstrom, b = 12.173 (2) angstrom, c = 13.387 (3) angstrom, alpha = 79.53 (3)-degrees, beta = 72.48 (3)-degrees, gamma = 70.93 (3)-degrees, V = 1198.2 (4) angstrom 3, and Z = 2. The Zn(II) ions are in a distorted octahedral environment composed of three facially coordinated amine nitrogen, two carboxylate oxygen atoms, and a water molecule. The two carbonyl oxygen atoms of the carboxylato groups are intramolecularly hydrogen bonded to the coordinated water molecule. In aqueous solution in the absence of coordinating ligands the L'Zn fragment was found to generate the di-mu-hydroxo-bridged dinuclear species [L'2Zn2(mu-OH)2](ClO4)2 (3). Crystal data: space group P2(1)/n, a = 8.703 (2) angstrom, b = 8.325 (2) angstrom, c = 20.470 (4) angstrom, beta = 90.96 (3)-degrees, V = 1482.9 (6) angstrom 3, and Z = 2. The Zn(II) ions are in a distorted square base pyramidal environment (five-coordinate). In the presence of excess sodium acetate L'Zn fragments form the dinuclear species [L'2Zn2(mu-OH)(mu-O2CCH3)2](ClO4).H2O (4). Crystal data: space group P4(1)2(1)2, a = 10.90 (1) angstrom, c = 27.86 (1) angstrom, V = 3310.0 (10) angstrom 3, and Z = 4. The dinuclear cation contains the (mu-hydroxo)bis(mu-acetato)dizinc(II) core and two tridentate macrocyclic capping ligands. Both zinc ions are in an octahedral ligand environment. Complexes 3 and 4 serve as structural models for the spatial arrangement of the two zinc(II) ions in the active sites of the enzymes phospholipase C from Bacillus Cereus and leucine aminopeptidase from bovine lens, respectively.