Self-ordering of metallogrid complexes via directed hydrogen-bonding

Abstract

Reaction of imidazole aldehydes with dihydrazino derivatives of 2-phenylpyrimidine provides a family of bis(acylhydrazone) ligands which form [2 × 2] metallogrid complexes with transition metal ions including Fe(II), Co(II), Cu(II) and Zn(II). The free ligands show H-bonding interactions, both donor and acceptor, largely involving the imidazole units, while binding of the metal ions occupies all the acceptor sites and leaves only the pyrrolic-NH site as an H-bond donor, although its deprotonation by a strong base can regenerate an acceptor. These H-bonding interactions have been studied by ¹H NMR spectroscopy in solution and in the solid state by means of several crystal structure determinations. The Fe(II) grids appear to be exclusively high-spin species over a wide temperature range in solution. In the solid state various forms of spin-crossover behaviour can be observed between 1.8 and 300 K, which has been rationalised in terms of the varied forms of hydrogen-bonding possible in the crystalline state.