Iron(ii) and cobalt(ii) complexes of tris-azinyl analogues of 2,2′:6′,2″-terpyridine

The syntheses of 2,6-di(pyrid-2-yl)pyrazine (L1), 2,6-di(pyrazinyl)pyridine (L2), 2,2′:6′,2″- terpyrazine (L3), 2,6-di(pyrimidin-4-yl)pyridine (L4), 2,6-di(1,2,4-triazin-3-yl)pyridine (L5), 4-hydroxy-2,6-di(pyrazinyl) pyridine (L6) and 4-hydroxy-2,6-di(pyrimidin-2-yl)pyridine (L 7) are described. Homoleptic iron(ii) and cobalt(ii) complexes of these ligands have been prepared and, in four cases, structurally characterised. The iron complexes are all low-spin. However, while the cobalt complexes of the pyrazine-rich ligands L2, L3 and L6 are all predominantly low-spin in the solid state, the other cobalt complexes are essentially high-spin between 5-300 K. The voltammetric M(iii)/(ii) (M = Fe or Co) oxidations and metal- or ligand-based reductions all become more anodic as the nitrogen content of the ligands increases, which correlates well with Lever's additive electrochemical parameters for the heterocyclic donor groups in each complex. This journal is © The Royal Society of Chemistry 2013.