Structural diversities and magnetic properties of azido- and dicyanamido-bridged coordination polymers with 4,5-diphenylimidazole as a terminal ligand

Abstract

With the aim of assessing the role and impact of pseudohalides on the molecular and supramolecular structures of copper(II)/heavily substituted imidazole complexes, the synthesis and characterization of the complexes {[Cu(N₃)₂(HL)]}_n (1), {[Cu{N(CN)₂}₂(HL)]·Me₂CO}_n (2·Me₂CO) and [Cu(NCO)₂(HL)₂]·MeCN (3·MeCN) have been carried out; HL is the 4,5-diphenylimidazole ligand. The organic molecule behaves as a monodentate ligand through the pyridine-type nitrogen atom of the imidazole ring. The 1D polymer 1 is made up of undulating {–Cu–(N₃)₂–Cu–(N₃)₂–} chains, with the HL ligands extending from both sides of the chains. The square pyramidal metal ions are alternately doubly bridged by two different types (basal–basal and basal–apical) of end-on azido groups. In 2·Me₂CO, the N(CN)₂⁻ ions behave as end-to-end (μ-1,5 or 2.101) ligands forming a 2D polymeric lattice, consisting of four-membered Cu^II rings interconnected by four dicyanamido bridges; the five-coordinate Cu^II ion adopts a geometry intermediate between square pyramidal and trigonal bipyramidal. The metal centre in the mononuclear complex 3·MeCN is bonded to two HL ligands and two terminal isocyanato groups; the coordination geometry of Cu^II is closest to a seesaw conformation. The crystal structures of the complexes are built with a variety of supramolecular interactions, including the synthons N−H⋯X (X = N and O), which are critically discussed. The IR spectra of the compounds are discussed in terms of the coordination modes of the pseudohalido ligands. The magnetic properties of 1 and 2 have also been studied in the temperature and field ranges of 1.8–300 K and 0–50 kOe, respectively. Complex 1 exhibits both ferromagnetic and antiferromagnetic Cu^II⋯Cu^II exchange interactions propagated through the two different end-on bi-azido bridges, whereas the exchange interactions are negligible (if any) in the 2D polymer 2 as a consequence of the μ-1,5 ligation mode of the dicyanamido ligand and the resultant long Cu^II⋯Cu^II distances.