A 3D Coordination Polymer Based on <i>Syn-Anti</i> Bridged [Mn(RCOO)₂]_n Chains Showing Spin-Canting with High Coercivity and an Ordering Temperature of 14 K

Abstract

A new 3D manganese(II) coordination polymer, formulated as [Mn3(HL)6] (1) (where H2L = 6-hydroxypicolinic acid), has been hydrothermally synthesized and characterized by single-crystal X-ray crystallographic analysis along with other spectroscopic and magnetic techniques. Structural analysis shows that the compound crystallizes in the monoclinic C2/c space group and is a non-porous 3D coordination polymer formed by three different Mn(II) centres connected by 6-hydroxypicolinic acid ligands in their keto form. Each Mn(II) centre shows a distorted octahedral coordination environment. Neighbouring Mn(II) centres are connected by two different syn-anti bridging carboxylate groups to form regular coordination chains. There are two different [Mn2(RCOO)2] units along the chain, formed by two crystallographically independent Mn centres (Mn1 and Mn2). These chains are further connected by HL− ligands to form a 3D coordination network. Interestingly, both the hydroxy and the carboxylate groups of the ligands are deprotonated and coordinated to the metal centres, whereas the pyridyl group is protonated and uncoordinated, although it participates in strong hydrogen bonding interactions with oxygen atoms of the HL− ligand, as shown by the Hirshfeld surface analysis. Both the absorption and emission spectra of the compound have also been measured. Variable temperature magnetic studies reveal the presence of a spin-canted antiferromagnetic behaviour with a high coercivity of 40 mT at 2 K and an ordering temperature of 14 K.

Keywords

• 3D coordination polymer
• manganese(II)
• 6-hydroxypicolinic acid
• keto-enol tautomerism
• <i>syn-anti</i> carboxylate
• spin-canting