Structural diversity and magnetic properties of five copper–organic frameworks containing one-, two-, and three-types of organic ligands

Abstract

Five novel compounds {[Cu(CMA)]·0.8H₂O}_n (1), {[Cu(CMA)(bpy)_0.5]·0.5DMF}_n (2), {[Cu(CMA)(bpy)(H₂O)]·0.5H₂O}_n (3), {[Cu₂(CMA)(DPA)(bpy)₂(H₂O)]ClO₄}_n (4) and {[Cu₃(CMA)(DPA)(bpy)₄(OH)](ClO₄)₂·3H₂O)}_n (5) (H₂CMA = 3-(carboxymethoxy)-5-methylbenzoic acid, HDPA = 2-(3,5-dimethylphenoxy)acetic acid, bpy = 4,4′-bipyridine) were synthesized and characterized by single crystal X-ray diffraction. Interestingly, the kinds of ligands included in these compounds are different: 1 contains single-ligand CMA²⁻; 2 and 3 comprise two kinds of ligands (CMA²⁻ and bpy); 4 and 5 cover three kinds of ligands (CMA²⁻, DPA⁻ and bpy). Structural analyses reveal that 1–3, and 5 are three-dimensional (3D) frameworks, while 4 is a 2D layer. Noteworthily, 1 possesses two types of channels: six-star and hexagonal ones. 3 displays a three-fold interpenetrating 3D framework. The structural diversity of the compounds may have originated from different anions, solvents and temperatures. Variable-temperature magnetic susceptibility measurements were carried out on compounds 1, 2 and 4, and the magnetic properties are dramatically different due to the structural diversities. The magnetic data of 1 shows an antiferromagnetic interaction with J = −54.84 cm⁻¹ estimated from the Bonner–Fisher model. The magnetic data of 2 was least-square fitted to the Blenaey–Bowers equation with J = −131.01 cm⁻¹, indicating the existence of a strong antiferromagnetic interaction between two adjacent Cu²⁺. The magnetic data of linear tetranuclear structure 4 was best fitted to the expression derived from the Hamiltonian H = −2(2J₁S₁S₂ + J₂S₁S_1*). The best fitting parameters are J₁ = −17.48 cm⁻¹ and J₂ = −65.26 cm⁻¹, which also indicate an antiferromagnetic interaction. Simultaneously, the magneto-structural relationship was discussed.