FORMATION OF MIXED SPIN-STATE MACROCYCLIC DINICKEL(II) COMPLEXES THROUGH VARIATION OF HOLE SIZE

Dinuclear nickel(II) complexes of two tetraaminodiphenol macrocyclic ligands in which one (H2L1) has two -NH(CH2)3NH- units and the other (H1L2) contains one -NH(CH2)3NH- and one -NH(CH2)2NH-moiety have been studied. In the inclusion complex [Ni2L1(H2O)4][ClO4]2.4NH2CONH2 1, both metal centres are in octahedral configuration. On reaction with pyridine (py), complex 1 transforms into the square-pyramidal complex [Ni2L1(PY)2] [ClO4]2. The macrocycle H2L2 forms the mixed spin-state complex [Ni2L2(H2O)2]I2 2 in which one metal centre is square planar and the other octahedral. On reaction with pyridine, complex 2 produces the square-planar-square-pyramidal complex [Ni2L2(py)] 12 4; the low-spin Ni2+ of both 2 and 4 is accommodated by the smaller N2O2 cavity provided by the phenolic oxygens and -NH(CH2)2NH- nitrogens. The redox properties of complexes 1 and 2 have been studied by cyclic voltammetry and their crystal structures determined. Complex 1: a = 7.530(l), b = 26.499(3), c = 11.434(l) angstrom, beta = 96.89(1)-degrees, Z = 2, R = 0.051 and R' = 0.059. Complex 2: a = 11.386(l), b = 20.094(2), c = 13.158(l) angstrom, beta = 102.16(l)-degrees, Z = 4, R = 0.050, R' = 0.059.