A three-dimensional ferromagnet based on linked copper–azido clusters

Abstract

Two novel three-dimensional coordination polymers [Cu₆(N₃)₁₂(N-Eten)₂]_n (1) (N-Eten = N-ethylethylenediamine) and {[Cu₉(N₃)₁₈(1,2-pn)₄]·H₂O}_n (2) (1,2-pn = 1,2-diaminopropane) have been synthesized by the self-assembly reactions of Cu(NO₃)₂·3H₂O, NaN₃ and small diamine ligands. Their molecular structures were determined by single-crystal X-ray diffraction. Complex 1 is composed of a neutral 3D coordination framework based on unprecedented hexanuclear copper(II) clusters which features three types of bridging modes for azide (µ-1,1, µ-1,3 and µ-1,1,3). Complex 2 is a novel 3D coordination polymer featuring octanuclear copper–azido clusters and [Cu(diamine)₂]²⁺ units which are linked by azido bridges. Magnetic studies for complex 1 show ferromagnetic ordering at 3.5 K, where the azido bridges mediate ferromagnetic coupling between adjacent Cu(II) ions. The magnetic data for 1 were fitted to a uniform hexanuclear copper model which yielded g = 2.21, J = 6.26 cm⁻¹, zJ′ = 0.39 cm⁻¹. Complex 2 shows ferromagnetic coupling in the octanuclear unit and antiferromagnetic interaction between neighboring units.