New examples of dinuclear copper complexes with ferromagnetic interactions mediated by μ-1,1 bridging azido and nitrito groups: structures and magnetic properties of [L 2(N 3) 2Cu 2] and [L 2(NO 2) 2Cu 2]·H 2O (L=7-amino-4-methyl-5-aza-3-hepten-2-onato(1−))

Abstract

The reaction of L 2Cu 2OAc 2 ( L = 7amino-4-methyl-5-aza-3-hepten-2-onato(−1); OAc = acetate ion) with NaN 3 and NaNO 2 yields [L 2(N 3) 2Cu 2] ( 1) and [L 2(NO 2) 2Cu 2]·H 2O ( 2), respectively. The azido complex crystallizes in the triclinic space group P 1 with a = 8.261(1), b = 9.176(1), c = 7.915(1) A ̊ , α = 113.06(1), γ = 108.90(1)°, Z = 1 . The nitrito complex also crystallizes in the triclinic space group P 1 with a = 11.523(1), b = 11.532(1), c = 112.22(1), β = 91.33(1), γ = 92.06(1)°, Z = 2 . In both cases the structure consists of neutral dinuclear entities resulting from the pairing of two mononuclear units via single-atom bridges connecting an equatorial position of a copper centre to an axial position of the other one. The copper ions adopt a (4 + 1) square-based geometry in the azido complex while (4 + 1) and (4 + 2) environments are present in the nitrito complex. Analysis of the thermal variation of the magnetic susceptibility shows that in both complexes, the two spins are ferromagnetically coupled within the dimer while an antiferromagnetic coupling is operative between dinuclear entities. Both types of interactions are larger in the case of the azido complex ( J = 24 cm −1, J′ = 1.6 cm −1) than for the nitrito complex ( J = 8 cm −1, J′ = −0.2 cm −1).