Synthesis and characterization of the pentadentate macrobicyclic ligand, 14-thia-1,4,8,11-tetraazabicyclo[9.5.3]nonadecane (L1) and its nickel(II) complexes.: X-ray crystal structure of [Ni(L1)(ClO4)](ClO4)•2[Ni(L1)(OH2)](ClO4)2•6H2O

The pentadentate macrobicycle,14-thia-1,4,8,11-tetraazabicyclo[9.5.3]nonadecane (L1), has been synthesized by high dilution cyclization of 1-thia-4,8-diazacyclododecane ([10]aneN(2)S) (2) with N,N'-bis(alpha -chloro acetamido) propane (3) and subsequent reduction of the di-oxo intermediate. The structure of the [Ni(L1)(ClO4)](ClO4).2[Ni(L1)(OH2)](ClO4)(2). 6H(2)O complex (monoclinic, P2(1)/c, a = 13.9261(4) Angstrom, b = 30.279(2) Angstrom, c = 17.1248(3) Angstrom, beta = 94.5065(3)degrees) at R = 0.039 (R-w = 0.034) for 911 parameters using 18 266 reflections with I > 3 sigmaI has been determined. The ligand adopts a trans-III configuration. The Ni(II) ion is pseudooctahedral with Ni-S = 2.3896(10) Angstrom in [Ni(L1)(ClO4)](+) and 2.4193(10) Angstrom, 2.4225(10) Angstrom, in the two [Ni(L1)(H2O)](2+) cations. Both nickel(II) and nickel(III) complexes are six-coordinatein solution. Oxidation of the [Ni(L1)(OH2)](2+) complex with K2S2O8 in aqueous solution yielded an ESRactive Ni(III) species and the frozen solution spectrum displayed axial symmetry with g(perpendicular to) = 2.159 and g(parallel to) = 2.024. In CH3CN, the [Ni(L1)(solv)](2+) complex showed two reversible redox waves corresponding to the Ni2+/+ couple at E-1/2 = -1.807 V vs. Fc(+/0) and Ni3+/2+ couple at E-1/2 = 0.715 V vs. Fc(+/0).