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

Abstract

The 4,4′-bipyridine (4,4′-bipy) and 3,6-bis(imidazolyl)pyridazine (bimpydz) bridged dinuclear copper(II)–diethylenetriamine (dien) complexes, [{Cu(dien)}₂(µ-diimine)][NO₃]₄·xH₂O (diimine = 4,4′-bipy, x= 2 1; diimine = bimpydz, x= 0 5), [{Cu(dien)}₂(µ-diimine)][BF₄]₄·4MeCN (diimine = 4,4′-bipy 2 or bimpydz 6) and [{Cu(dien)}₂(µ-bimpydz)]Cl₄·4H₂O 4, have been synthesised and characterised. Reaction of the tetrafluoroborates, 2 and 6, with NaNO₂ yields the nitrites [{Cu(dien)}₂(µ-diimine)][NO₂][BF₄]₃·xMeCN (diimine = 4,4′-bipy, x= 0 3; diimine = bimpydz, x= 0.5 7). 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(µ-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 Å, 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 µ-nitrito-κO : κN 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.