Eight novel metal diphosphonates based on 2-(4-pyridinyl)-1-hydroxyl-1,1-ethylidenediphosphonate: syntheses, structures, and magnetic properties

Abstract

A systematic exploration of a series of hydrothermal reactions of 2-(4-pyridinyl)-1-hydroxyl-1,1-ethylidenediphosphonic acid (4-pyHhedpH3) with manganese, cobalt and copper salts resulted in eight new compounds, namely, Mn(4-pyHhedpH)·H2O (1), Co(4-pyHhedpH)·H2O (2), Co(4-pyHhedpH2)(C2O4)0.5(H2O)·H2O (3), Co3(4-pyHhedpH)2(C2O4)(H2O)2 (4), Cu(4-pyHhedpH2)2 (5), Cu(4-pyHhedpH) (6), CuICuII3(4-pyhedpH0.5)2 (7) and Cu3(4-pyHhedpH)2(C2O4) (8). Compounds 1 and 2 are isostructural and have ladder-like structures in which the {M2(μ-O)2} (M = Mn, Co) dimer units are connected by O–P–O bridges, whereas, compound 3 has a one-dimensional chain structure, where the Co atoms are alternatively linked by C2O42− and O–P–O bridges. Compound 4 contains one chain similar to that of compound 3, while, the chains are further connected by O–P–O bridges to generate a brick-like layer. Compound 5 has a mononuclear structure in which the central Cu ion is chelated by four O atoms from two 4-pyHhedpH ligands, giving a quadrilateral planar coordination shape. Compound 6 has chain-like structures, where {Cu2(μ-O)2} dimers are connected by edge-shared {CuO5} square pyramids to form infinite chains. In compound 7, the {Cu3(O)4} trimers are bridged by O–P–O groups to form infinite chains which are further connected by the pyridinyl groups and {O–CuI–O} units to afford layers. Compound 8 has a two-dimensional structure similar to that of compound 4. The temperature-dependent magnetic susceptibility measurements show dominant antiferromagnetic interactions in compounds 1–4 and 6–8 mediated through O–P–O and/or μ-O bridges between the metal centers. The magnetization measurements reveal that compound 2 shows field-induced magnetic transition at low temperature.