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)

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 MnII 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 CuII 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 = -J1ΣS2i·S2i+1 - J2ΣS2i+1·S2i+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. © The Royal Society of Chemistry 1999.link_to_subscribed_fulltex