A series of manganese–carboxylate coordination polymers exhibiting diverse magnetic properties

Abstract

The hydrothermal reactions of an asymmetrical 4-(4-carboxyphenylamino)-3,5-dinitrobenzoic acid (H₂cpdba), MnCl₂·4H₂O, or together with 2,2′-bipyridine (2,2′-bpy) or 4,4′-bipyridine (4,4′-bpy) afford three novel molecule-based magnetic coordination polymers [Mn(cpdba)]_n (1), {[Mn₂(cpdba)₂(2,2′-bpy)₂(H₂O)₂]·H₂O}_n (2) and {[Mn₂(cpdba)₂(4,4′-bpy)]·2H₂O}_n (3). Compound 1 has a 3D acentric coordination network containing carboxylate-bridged 1D ladder-like manganese chains with spin-canted antiferromagnetism (J = −3.51 cm⁻¹ for the coupling along the ladder legs, and zJ′ = 0.22 cm⁻¹ for coupling along the ladder rungs), whereas compounds 2 and 3 crystallize in the centrosymmetric space groupsP and C2/c, respectively. 2 exhibits a 1D chain structure, which is extended into a 3D supramolecular network by π–π stacking interactions, while 3 features a quite complex 3D network built up from the cpdba²⁻ and 4,4′-bpy spacers as well as the carboxylate-bridged Mn(II) chains. Both 2 and 3 show weak antiferromagnetic coupling interactions (J = −0.55 cm⁻¹ for 2), and a field-induced spin-flop magnetic transition can also be observed in 2 at ca. 3.2 T at 2 K.