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.