Pyrazine-imide complexes: reversible redox and MOF building blocks

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)(H(2)O)(2)]BF(4), [Cu(II)(dpzca)(H(2)O)(3)](2)SiF(6). The crystal structures of Hdpzca, [Co(II)(dpzca)(2)], [Cu(II)(dpzca)(2)], {[Co(III)(dpzca)(2)](BF(4))}(2)·5CH(3)CN and [Cu(II)(dpzca)(H(2)O)(3))](2)SiF(6)·2H(2)O 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)(2)Ag](NO(3))(2)·2H(2)O}n and {([Ni(II)(dpzca)(2)Ag(I)(1/2)](1/2NO(3))(xH(2)O}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 E(m)(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).