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)(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 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 = − JS 1 · S 2, 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 ( J eo) and the other via the EE bridge ( J ee). The alternating chain model with ferromagnetic and antiferromagnetic interactions based on the exchange Hamiltonian H = −∑ i [ J 1 S 2 i · S 2 i + 1 + J 2 S 2 i · S 2 i − 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.