Structural diversity and magnetic properties of six cobalt coordination polymers based on 2,2'-phosphinico-dibenzoate ligand.

Abstract

Six novel Co(ii) coordination polymers, namely, [Co10L6(OH)2(H2O)9]·10.5H2O (1), [Co3L2(3-abpt)2]·4H2O (2), [Co3L2(4-azpy)2(H2O)2(EtOH)] (3), [Co3L2(4,4'-bipy)2(H2O)2(MeCN)] (4), [Co3L2(4,4'-bipy)2] (5), and [Co5L2(OH)2(ina)2(H2O)2] (6) (H3L = 2,2'-phosphinico-dibenzoic acid, 3-abpt = 4-amino-3,5-bis(3-pyridyl)-1,2,4-triazole, 4-azpy = 4,4'-azobispyridine, 4,4'-bipy = 4,4'-bipyridine, Hina = isonicotinic acid), have been hydrothermally synthesized and their magnetic properties have been characterized. The L3- anion displays six types of coordination modes in the compounds. Compound 1 exhibits a novel 1D ladder-like structure, which consists of non-centrosymmetric Co10 units. Compounds 2-4 comprise 2D networks assembled from Co3L2 chains and N-heterocyclic linkers. Compound 5 comprises a 3D framework built from six neighboring parallel Co3L2 ladders bridged by 4,4'-bipy linkers. Compound 6 features a 3D framework that exhibits pcu topology with the Schläfli symbol of (412·63) using a pentanuclear [Co5(OH)2]8+ cluster as the node. Variable-temperature magnetic susceptibility studies indicate that the six coordination polymers exhibit remarkable magnetic behavior such as spin-canted antiferromagnetism and spin glass, which were found to coexist in compound 6.