Synthesis, crystal structure, and magnetic properties of two new Cu(II) complexes with end-to-end azido bridging ligands

Abstract

Two new copper(II) complexes, derived from an end-to-end azido linker and two different tridentate Schiff base ligands, have been synthesised and their crystal structures determined by X-ray diffraction methods. They are the single azido-bridged [Cu(L1 − H)(μ-1,3-N₃)] _n(H₂O)_2n (1) chain and the dinuclear [Cu₂(L2)₂(μ-1,3-N₃)₂(ClO₄)₂] (2) where L1 and L2 are two different tridentate Schiff bases obtained by condensation of salicylaldehyde with 4-(2-aminoethyl)morpholine and of pyridine-2-aldehyde with N,N-dimethylpropane-1,3-diamine, respectively. Structural results show that each copper(II) centre in 1 is in a square pyramidal geometry while in 2 the geometry of copper(II) is octahedral with one coordinated perchlorate in both copper(II) complexes. Variable temperature magnetic susceptibility data in the range of 300–2 K for 1 reveal the existence of intrachain weak antiferromagnetic interactions through the end-to-end azido coupler, while the data for 2 show the existence of unusual intradimer ferromagnetic interactions through the end-to-end azido pathway, which almost always leads to an anti-parallel spin orientation. Fitting of the data for 1 using the Bonner–Fisher model for an antiferromagnetically coupled chain of S  = 1/2 local spins resulted in the parameters J  =  −4.3 cm⁻¹, g  = 2.1 and R  = 4.0 × 10⁻⁴. Temperature dependent susceptibility data for 2 were fitted using the Bleaney–Bowers expression for a Cu(II) dimer, which led to the parameters J  =  +2.4 cm⁻¹, g  = 2.11 and ρ  = 0.003.