Binuclear Copper(II) Complexes of Some Tetradentate Pyridyl Phthalazine Ligands. Structure, Electrochemistry and Magnetism - Crystal-Structure of Aqua-µ-[1,4-Di-(4',6'-Dimethylpyridin-2'-Ylamino)-Phthalazine-N^1',µ-N² ,µ-N³,N^1'']-µ-Hydroxo-Dinitratodicopper(II) Nitrate

Abstract

The molecular structure of aqua-μ-[1,4-di(4′,6′-dimethylpyridin-2′- ylamino )phthalazine-N^1′,μ-N²,μ-N³,N^1′]-μ- hydroxo-dinitratodicopper (II) nitrate has been determined by single-crystal X-ray diffractometry . The compound is triclinic, space group Pī , with two molecules in the unit cell of dimensions a 7.8064(11), b 12.9137(14), c 14.8564(14), α 69.857(8), β 80.074(10), γ 83.659(11). The structure was refined by least-squares to a residual of 0.057 for 2806 reflections. The binuclear centre in the complex involves a five-coordinate and a tetragonally distorted six-coordinate copper atom, each with a coordinated, bidentate nitrate, a copper-copper separation of 3.156 Ǻ and a Cu-O(H)-Cu bridge angle of 113.7°. This complex, and other related systems, exhibit low room-temperature magnetic moments (< 1.2 BM), suggesting antiferromagnetically coupled binuclear copper centres , and in the case of the complex [Cu₂( paps )(OH)Cl₃].3H₂O variable- temperature magnetic data indicate moderately strong exchange with -2J = 432 cm^-1. Very high redox potentials are observed for these complexes [0.00-0.83 V (v. s.c.e .)] involving two-electron transfer in one step or two separate steps.