Field-induced single-ion magnet behavior in a cobalt(II) coordination polymer constructed by a mixed bipyridyl-tetracarboxylate strategy

Abstract

A porous two-dimensional (2D) cobalt(II) metal–organic framework (MOF), {[Co(H2tbca)(bpb)(H2O)2]·bpb}n (H4tbca = 1,2,4,5-Benzenetetracarboxylic acid; bpb = 1,4-bis(pyrid-4-yl)benzene), was synthesized and structurally characterized. Single crystal X-ray diffraction analysis indicates that the monometallic Co2+ ion acted as coordination nodes in a distorted octahedral geometry and bridged by H2tbca2− and bpb ligands, giving rise to a porous 2D sql network. Thermal analysis reveals high thermal stability of the framework material even losing its guest molecules. Magnetic studies showed that the six-coordinated Co2+ ions exhibit large easy-plane magnetic anisotropy with the zero-field splitting parameter D = 62.1 cm−1. For the presence of significant single-ion magnetic anisotropy, single-ion magnet (SIM) behavior through combined Direct and Raman mechanisms was evidenced with the effective energy Ueff = 31.8 cm−1. The forgoing result provides a new 2D cobalt(II) SIM-MOF and a potential bipyridyl-tetracarboxylate approach for the construction of SIM frameworks.