Polar metal phosphonate containing unusual μ(4)-OH bridged double chains showing canted antiferromagnetism with large coercivity.

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.