Crystal structures and magnetic properties of two alternating azide-bridged complexes [{M(dmbpy)(N3)2}n] (M = Mn or Cu; dmbpy = 4,4′-dimethyl-2,2′-bipyridine)†

Abstract

Single crystals of complexes [{Mn(dmbpy)(N₃)₂}_n] 1 and [{Cu(dmbpy)(N₃)₂}_n] 2 (dmbpy = 4,4′-dimethyl-2,2′-bipyridine) were obtained from aqueous solutions containing 4,4′-dimethyl-2,2′-bipyridine, metal ions and sodium azide, and their structures determined by X-ray diffraction methods. The structure of 1 is a neutral two-dimensional network in which each Mn^II is bridged to three other metal ions through alternating single end-to-end and double end-on azido bridges. Compound 2 is a neutral chain in which the Cu^II is alternately bridged by double asymmetrical end-on and end-to-end azide groups. The magnetic properties of 1 and 2 have been investigated in the temperature range 5–300 K. Alternating ferro- and antiferro-magnetic interactions exist in the two compounds. A theoretical model has been developed for an S = 5/2 alternating ferromagnetic–antiferromagnetic coupled 2-D system: the exchange parameters obtained with this model are J/k = –7.7 K, zJ′/k = 2.5 K and g = 2.0 for 1. An S = 1/2 alternating ferromagnetic–antiferromagnetic coupled chain with the spin Hamiltonian H = –J₁ΣS_2i·S_2i+1 – J₂ΣS₂i+1·S_2i+2 leads to: J₁/k = 11 K, J₂/k = –87 K and g = 2.06 for 2. The natures and the magnitude of the alternating ferro- and antiferro-magnetic interactions in both compounds are discussed based on their structures.