Formation of mixed spin-state macrocyclic dinickel(II) complexes through variation of hole size

Abstract

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.