Polar metal phosphonate containing unusual μ4-OH bridged double chains showing canted antiferromagnetism with large coercivity

Abstract

The first examples of metal phosphonates based on an asymmetrical 2-(phosphonomethyl)benzoic acid (2-pmbH₃) are reported, namely, Co₂(μ₄-OH)(2-pmb) (1) and Cu₄(μ₃-OH)₂(2-pmb)₂ (2). Both crystallize in polar space groups and show layered structures. Compound 1 contains unusual μ₄-OH bridged double chains of {Co₂(μ₄-OH)O₃}, inter-connected by the phosphonate groups. In 2, chair-like tetramers of Cu₄(μ₃-OH)O₂ are linked by both carboxylate and phosphonate groups. Magnetic studies reveal that compound 1 experiences canted antiferromagnetic ordering below 31.0 K with a large coercivity of 4.3 Tesla at 2 K.