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

Abstract

Dinuclear [Cu(aepi)(N3)2]2 (1) [aepi = 1-(2-aminoethyl)piperidine] and 1D chain [Cu(aepy)(N3) 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 μ-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 = -JS1 • S2, affording parameters of g = 2.093(1), J = -3.06(1) 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 (Jeo) and the other via the EE bridge (Jee). The alternating chain model with ferromagnetic and antiferromagnetic interactions based on the exchange Hamiltonian H = -∑iS2i • S2i + 1 + J2S 2i • S2i - 1] was employed, leading to g = 2.076(2), J1 = -3.22(5) cm-1, J2 = 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 J1 and J2 are ascribed to Jeo andJee, respectively. These assignments are also ascertained by MO calculations using a spin dimer model. © 2004 Elsevier Ltd. All rights reserved.