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), Cu^ICu^II₃(4-pyhedpH_0.5)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–Cu^I–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.