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 (H2L2) contains one -NH(CH2)3NH- and one -NH(CH2)2NH- moiety have been studied. In the inclusion complex [Ni2L1(H2O)4][ClO4]2·4NH2CONH21, 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]I22 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)]I24; 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(1), b= 26.499(3), c= 11.434(1)Å, β= 96.89(1)°, Z= 2, R= 0.051 and R'= 0.059. Complex 2: a= 11.386(1), b= 20.094(2), c= 13.158(1)Å, β= 102.16(1)°, Z= 4, R= 0.050, R'= 0.059