Dicopper(II) complexes of a binucleating N4 macrocycle containing mono- and di-atomic bridges; magnetic interactions mediated by alkoxo- and diaza-bridging ligands. Crystal structures of [Cu2(L1)(pz)2][ClO4]2, [Cu2(L1)(OEt)2(NCS)2], and [Cu2(L1)(OMe)2(MeCN)2][BPh4]2

Abstract

Dicopper(II) complexes of 20-membered N₄ binucleating macrocycles L¹–L³ derived by a cyclic [2 + 2] condensation of diformylthiophene or diformylfuran with the appropriate diamine have been synthesised and characterised by analytical, spectroscopic, magnetic, and X-ray diffraction methods. A pair of bridging ligands, either alkoxo, OR^–(R = H, Me, or Et), or diaza (pyrazolate or 1,2,4-triazolate), links the Cu^II ions. The crystal structure of three compounds [Cu₂(L¹)(pz)₂][ClO₄]₂(1), [Cu₂(L¹)(OEt)₂(NCS)₂](6), and [Cu₂(L¹)(OMe)₂(MeCN)₂][BPh₄]₂(7) have been determined by X-ray diffraction (Hpz = pyrazole). In structures (6) and (7) the copper(II) ions have a trigonal-bipyramidal environment, with ethoxy [(6)] or methoxy [(7)] bridges in a position axial to one Cu^II and equatorial to the other. Despite the parallel disposition of the d_z² magnetic orbitals, strong antiferromagnetic superexchange is observed for this and the other parallel-planar alkoxobridged dimer described. In structure (1), the copper co-ordination environment is square planar, with cis disposed pyrazolate bridges. Moderate antiferromagnetic exchange is present in (1) and the other diaza compounds, and well defined triplet e.s.r. spectra are observed.