Nitrate and nitrite-ligated 3,6-bis(imidazolyl)pyridazine-bridged dinuclear copper(II) cations with copper-copper separations similar to that in Achromobacter cycloclastes nitrite reductase

The 4,4'-bipyridine (4,4'-bipy) and 3,6-bis(imidazolyl)pyridazine (bimpydz) bridged dinuclear copper(II)-)diethylenetriamine (dien) complexes, [{Cu(dien)}(2)(mu-diimine)][NO3](4) . xH(2)O (diimine = 4,4'-bipy, x = 21; diimine = bimpydz, x = 0.5), [{Cu(dien)}(2)(mu-diimine)][BF4](4) . 4MeCN (diimine = 4,4'-bipy 2 or bimpydz 6) and [{Cu(dien)}(2)(mu-bimpydz)]Cl-4 . 4H(2)O 4, have been synthesised and characterised. Reaction of the. tetrafluoroborates, 2 and 6, with NaNO2 yields the nitrites [{Cu(dien)}(2)(mu-diimine)][NO2][BF4](3) . xMeCN (diimine = 4;4'-bipy, x =; 0 3; diimine = bimpydz, x = 0.57), Neither the chloride nor the nitrates react with NaNO2. Structural analysis of complexes 5 and 7 has shown that although they are both based on the dinuclear cationic unit, [{Cu(dien)}(2)(mu-bimpydz)](4+), in 5 the bimpydz bridge adopts a transoid arrangement of imidazole molecules, whereas in 7 it adopts a cisoid arrangement, giving Cu ... Cu separations of 13.28 and 12.88 Angstrom, respectively. In 5, the dications are linked by two axially co-ordinated nitrate anions, one strongly bound, the other very weakly bound, to give chains with a ladder-type motif. In 7, the dications are bridged by mu-nitrito-kappa O:kappa N moieties to form a chain with helical geometry. The copper(II)-nitrite interaction is novel; the anion bridges the weakly binding axial positions of two square-pyramidal copper atoms using the nitrogen lone pair and the syn lone pair of an oxygen.