Syntheses and crystal structures of Ni(II) complexes with pyridine-based macrocyclic ligands

Abstract

Three pyridine-based macrocyclic ligands, two containing one pyridine pendant arm (L1 and L2) and one containing piperazine rings in the macrocyclic scaffold (L3), with an increasing size of the macrocycle from 12-, 14- to 30-membered ring for L1–L3 were synthesized and characterized. A series of Ni(II) complexes with all these ligands, with molecular formulas [NiL1(CH3OH)](ClO4)2 (1), [NiL2(CH3CN)](ClO4)2 (2), and [Ni2L3(DMF)2(CH3CN)2](ClO4)4 (3) (DMF = N,N–dimethylformamide), was prepared and thoroughly characterized. Single crystal X-ray structural analysis confirmed that all the complexes have a coordination number of six and their geometries are close to octahedral. In the case of the mononuclear complexes 1 and 2, all the nitrogen atoms of the macrocycle are coordinated, however, in the dinuclear complex 3 with the piperazine-based ligand L3, two nitrogen donor atoms (of the total number of ten) are uncoordinated. The first coordination spheres of all the complexes are completed by solvent molecules. The values of effective magnetic moments, determined by the Evans method in solution, are 3.12, 3.19 and 4.36 µB for complexes 1, 2 and 3, respectively, which correspond well to the theoretical spin-only values.