Azido-bridged Cu(II) compounds with asymmetric end-to-end and end-on binding modes: magnetic assignments using a spin dimer model

摘要

Dinuclear [Cu(aepi)(N-3)(2)](2) (1) [aepi = 1-(2-aminoethyl)piperidine] and 1D chain [Cu(aepy)(N-3)(2)](n)(2) [aepy = 1-(2-aminoethyl)pyrrolidine] have been prepared and characterized by means of X-ray analysis and magnetic measurements. For 1, the Cu(II) centers are doubly bridged by end-on (EO) azido units in a basal-apical fashion. The molecular structure of 2 features magnetic centers that are linked by alpha-1,1,3 azido groups, forming a 1D chain with alternating EO and end-to-end (EE) azido bridging patterns. The magnetic data for the dinuclear complex 1 were fitted with the Bleaney-Bowers equation derived from the Hamiltonian H = -JS(1) . S-2, affording parameters of g = 2.093(1), J = -3.06(l) cm(-1) and zJ' = -1.32(3) cm(-1). This indicates that the EO azido group mediates an antiferromagnetic interaction. Complex 2 has two possible magnetic pathways: one is through the EO azido bridge (J(eo)) and the other via the EE bridge (J(ee)). The alternating chain model with ferromagnetic and anti ferromagnetic interactions based on the exchange Hamiltonian H = -Sigma(i)[J(1)S(2i) . S2i+1 + J(2)S(2i) . S2i-1] was employed, leading to g = 2.076(2), J(1) = -3.22(5) cm(-1), J(2) = 17.0(5) cm(-1) and zJ' = -1.34(6) cm(-1). By taking into account structural parameters of 1 and 2, it is rationally suggested that J(1) and J(2) are ascribed to J(eo) and J(ee), respectively. These assignments are also ascertained by MO calculations using a spin dimer model. (C) 2004 Elsevier Ltd. All rights reserved.