Formation in solution, synthesis and crystal structure of μ-oxalatobis[bis(2-pyridylcarbonyl)amido] dicopper(II)

Abstract

The compound μ-oxalatobis[bis(2-pyridylcarbonyl)amido] dicopper(II), [Cu 2{(NCsH 5CO) 2N} 2- (C 2O 4)] was synthesized and characterized by spectroscopy, EPR and diffraction methods. It crystallizes in the triclinic space group P 1 with cell constants: a=7.6793(6), b=9.238(2), c=10.007(2) Å, α=83.80(1), β=68.37(1) and γ=69.44(1)°; V=617.7(3) Å 3, D (calc., Z=2)=1.80 g cm −3, M r=667.6, F(000)=336, λ, (Mo Kα)=0.71069 Å, μ (Mo Kα)=17.895 cm −1 and T=295 K. A total of 3587 data were collected over the range of 1 ⩽ θ ⩽ 30°; of these, 2391 (independent and with I⩾2σ( I)) were used in the structural analysis. The final R and R w residuals were 0.049 and 0.053, respectively. The structure consists of neutral centrosymmetrical binuclear entities in which C 2O 4 2− acts in an asymmetrically bis-bidentate fashion. Each copper atom is in a square-pyramidal environment with the three nitrogen atoms of bis(2-pyridylcarbonyl)- amido anion and an oxygen atom of oxalate in the basal plane and another oxygen atom of oxalate occupying the apical position. The stability constants of the oxalato complexes of bis(2-pyridylcarbonyl)amidocopper( II) have been determined in dimethyl sulphoxide solution: log β 111=12.22 ± 0.05, log β 110=7.0 ± 0.1 and logβ 210=10.25 ± 0.1 at 25 °C and 0.1 mol dm −3 tetra-n-butylammonium perchlorate. Coordination modes of oxalate for this system are compared in DMSO and water in the light of thermodynamic and structural parameters