1,3,5-TRIAMINO-1,3,5-TRIDEOXY-CIS-INOSITOL, A NEW LIGAND WITH A REMARKABLE VERSATILITY FOR METAL-IONS .1. PREPARATION, X-RAY STRUCTURE, AND STABILITY OF THE NICKEL(II), COPPER(II), AND ZINC(II) COMPLEXES

Compounds of the composition M(taci)2(NO3)2.xH2O and M(taci)2Br2.XH2O (M = Ni, Cu, Zn, taci = 1,3,5-triamino-1,3,5-trideoxy-cis-inositol, 0 less-than-or-equal-to x less-than-or-equal-to 4) have been prepared from aqueous solution and characterized by spectroscopic methods (vis, EPR, NMR). Single-crystal X-ray analysis of M(taci)2Br2.4H2O revealed an isomorphous structure for Ni(II), Cu(II), and Zn(II) with space group Cmcm and Z = 4. Ni complex: a = 9.410 (5) angstrom, b = 11.383 (7) angstrom, c = 22.000 (13) angstrom. Cu complex: a = 9.391 (6) angstrom, b = 11.475 (7) angstrom, c = 21.924 (12) angstrom. Zn complex: a = 9.425 (5) angstrom, b = 11.431 (6) angstrom, c = 22.104 (11) angstrom. In contrast to Cr(taci)2(3+), where the ligands are coordinated to the metal via oxygen and nitrogen atoms, Ni, Cu, and Zn were exclusively bound to the three nitrogen atoms of taci, forming a MN6 octahedron. In the case of Cu, the significant distortion corresponds to the usual Jahn-Teller effect, whereas the distortion of the Ni and Zn complexes as provoked by the crystal packing is not significant. In accordance, the NMR data showed D3d symmetry for Zn(taci)2(2+) in solution. The formation constants beta-1 for M(taci)2+ and beta-2 for M(taci)2(2+) were investigated by potentiometric titration in aqueous solution (25-degrees-C, 0.1 M KNO3). pK of taci: 5.95, 7.40, 8.90 (estimated standard deviations <0.01). Ni: log beta-1 = 12.37 (1), log beta-2 = 20.94 (1). Cu: log beta-1 = 12.09 (1), log beta-2 = 18.79 (1). Zn: log beta-1 = 8.40 (1), log beta-2 = 13.56 (1). Two minor species, HCu(taci)23+ and the dimer Cu2(OH)2(taci)22+ , have also been identified. The permutation of the usual Irving Williams order is a consequence of the rigid ligand geometry which enforces facial coordination. The complex formation constants were compared with those of other triamines.