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: [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
)(
x
H
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).