Ferromagnetic coupling in the malonato-bridged copper(ii) chains [Cu(Im)2(mal)]n and [Cu(2-MeIm)2(mal)]n (H2mal = malonic acid, Im = imidazole and 2-MeIm = 2-methylimidazole)

Abstract

Two new malonato-bridged copper(II) complexes of formula [Cu(Im)₂(mal)]_n (1) and [Cu(2-MeIm)₂(mal)]_n (2) (Im = imidazole, 2-MeIm = 2-methylimidazole and mal = malonate dianion) have been prepared and their structures solved by X-ray diffraction methods. The [Cu(Im)₂(mal)] and [Cu(2-MeIm)₂(mal)] neutral entities act as monodentate ligands towards the adjacent copper(II) units through one of the two carboxylate groups, the OCO bridge exhibiting an anti-anti conformation. The environment of each copper atom in 1 and 2 is distorted square pyramidal: two carboxylate oxygen atoms from a bidentate malonate and two nitrogen atoms from two imidazole (1) or 2-methylimidazole (2) ligands form the equatorial plane whereas the apical position is occupied by a carboxylate oxygen from the malonate group of the neighbouring complex unit. The intrachain copper-copper separation is 6.036(2) (1) and 6.099(2) Å (2). The magnetic properties of 1 and 2 have been investigated in the temperature range 1.9–290 K. Overall, ferromagnetic behaviour is observed in both cases and the intrachain magnetic coupling (J) between the copper(II) ions through the carboxylato group is found to be 1.64 (1) and 0.39 cm⁻¹ (2) (the Hamiltonian being H = −JΣ_iS_i·S_i+1).