Matthew G. Cowan, Reece G. Miller, Sally Brooker

The synthesis of the symmetric pyrazine imide ligand, N-(2-pyrazylcarbonyl)-2-pyrazinecarboxamide, (Hdpzca) and five new first row transition metal complexes of it are reported: [M(II)(dpzca)2], M(II) = Fe, Cu, Zn; [Cu(II)(dpzca)(H2O)2]BF4, [Cu(II)(dpzca)(H2O)3]2SiF6. The crystal structures of Hdpzca, [Co(II)(dpzca)2], [Cu(II)(dpzca)2], {[Co(III)(dpzca)2](BF4)}2·5CH3CN and [Cu(II)(dpzca)(H2O)3]2SiF6·2H2O were determined and reveal an orthogonal positioning of the 'spare' pyrazine nitrogen atoms and 'spare' pairs of imide oxygen atoms. The [M(II)(dpzca)2] complexes are therefore useful six-coordinate building blocks for producing larger supramolecular assemblies. Two examples of secondary assembly of [M(II)(dpzca)2] complexes, with M = Co and Ni, with silver nitrate gave single crystals; {[Co(III)(dpzca)2Ag](NO3)2·2H2O}n and {([Ni(II)(dpzca)2Ag(I)1/2](1/2NO3)(xH2O}n were structurally characterised. The redox processes of [M(II)(dpzca)2], with M(II) = Fe, Ni, Cu and Zn, are reported and, as seen for M(II) = Co, reversible metal- and ligand-based redox processes are observed, with Em(M(II)/M(III)) values 0.15-0.24 V higher than for the analogous complexes of Hpypzca (non-symmetric pyridine/pyrazine imide ligand), and 0.35-0.36 V higher than for the complexes of Hbpca (symmetric pyridine imide ligand).