Pyrazine-imide complexes: Reversible redox and MOF building blocks

Abstract

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: [MII(dpzca)2], MII = Fe, Cu, Zn; [CuII(dpzca)(H2O)2]BF4, [CuII(dpzca)(H2O)3]2SiF6. The crystal structures of Hdpzca, [CoII(dpzca)2], [CuII(dpzca)2], {[CoIII(dpzca)2](BF4)}2·5CH3CN and [CuII(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 [MII(dpzca)2] complexes are therefore useful six-coordinate building blocks for producing larger supramolecular assemblies. Two examples of secondary assembly of [MII(dpzca)2] complexes, with M = Co and Ni, with silver nitrate gave single crystals; {[CoIII(dpzca)2Ag](NO3)2·2H2O}n and {([NiII(dpzca)2AgI1/2](1/2NO3)(xH2O}n were structurally characterised. The redox processes of [MII(dpzca)2], with MII = Fe, Ni, Cu and Zn, are reported and, as seen for MII = Co, reversible metal- and ligand-based redox processes are observed, with Em(MII/MIII) 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). This journal is