STRUCTURE AND REACTIVITY OF THE NICKEL(II) COMPLEX OF A NEW OPEN-CHAIN AMINE 6,6-BIS(4-AMINO-2-AZABUTYL)-1,4-DIAZACYCLOHEPTANE AND OF THE NICKEL(III) COMPLEX OF ITS MACROCYCLIC ANALOG - EFFECTS ON THE REDUCTION OF PERCHLORATE ION

The syntheses of the Ni(II) complex of the protonated form (HL1+) of a new open-chain hexaaza ligand L1 (L1 = 6,6-bis(4-amino-2-azabutyl)-1,4-diazacycloheptane) and of the corresponding macrocyclic analogue (H2L3(2+); L3 = 2,5,9,12,16,19-hexaaza-7-spiro[6.13]eicosane) are described. In the presence of perchlorate and iodide, the Ni(II) complex of HL1+ crystallizes with either one triiodide and two iodide ions or two triiodides and one iodide as counterions. The structure of [Ni(II)(HL1)]I7.H2O (P1BAR, triclinic, a = 9.317 (3) angstrom, b = 18.276 (5) angstrom, c = 9.132 (3) angstrom, alpha = 99.43 (3)degrees, beta = 72.89 (2)degrees, gamma = 87.54 (3)degrees, V = 1459 angstrom 3) has been refined to an R value of 0.0595 (R(w) = 0.0624) by using 2751 (I > 5-sigma(I)) of the 3807 reflections collected. The nickel ion adopts a square-planar geometry with an average Ni-N distance of 1.935 (14) angstrom. Iodine donors on each triiodide ion lie about 3.5 angstrom on each side of the Ni(II) center. In acidic perchlorate media containing chloride, the Ni(II) complex of H2L3(2+) crystallized as the trans-dichloronickel(III) complex. The structure of this Ni(III) species, [Ni(III)Cl2(H2L3)](Cl)(ClO4)2.2H2O (orthorhombic, noncentrosymmetric, space group P2(1)2(1)2(1) (No. 19), a = 10.996 (3) angstrom, b = 31.535 (8) angstrom, c = 7.808 (2) angstrom, has been refined to an R value of 0.0614 (R(w) = 0.0628) for 325 parameters by using 1249 reflections (I > 4-sigma(I)) of the 1500 collected. The complex is pseudooctahedral with an average Ni-N distance of 1.983 (14) angstrom and a Ni-Cl distance of 2.415 (6) angstrom. The Ni(III) species shows an axial ESR spectrum with g perpendicular-to = 2.17 and g parallel-to 2.02; A parallel-to = 30 G. The Ni2+/3+ couple is only quasi-reversible in 0.1 M lithium perchlorate or triflate media. However, in 1.0 M LiCl ([H+] = 0.1 M) a reversible wave at 0.57 V vs SCE was observed. Similar behavior is noted for the Ni(II) complex of the open-chain ligand HL1+. The two nitrogens of the 1,4-diazacycloheptane rings in the ligands L1 and L3 are not accessible to coordination. However, these nitrogens can be protonated and the presence of such secondary ammonium centers in the Ni(II) complexes of HL1+ and H2L3(2+) enhances a redox process between perchlorate ion and the Ni(II) centers. The formation of both the triodide anions in the preparation of the Ni(II) complexes of HL1+ and of the oxidized center in trans-dichloronickel(III) species is also explained in terms of such a redox reaction.