Syntheses, structures and magnetic properties of zig-zag chains of transition metals with O–P–O bridges

A novel series of linear chain coordination polymers, [NH4][MII(H2PO2)3(H2O)] where M = Mn, Co, Ni, has been obtained by the reaction of divalent metals salts with ammonium pyrophosphite, [NH4][H2PO2], in a methanol–water mixture. They crystallise in the monoclinic P 21/n cell and contain polar chains aligned with opposing polarity. Both bridging and terminal monodentate coordination modes are exhibited by the View the MathML sourceH2PO2-. Two types of hydrogen-bond between a coordinated water and a monodentate View the MathML sourceH2PO2- connect the chains into a 3D-network. The compounds have been further characterised by IR and UV–Vis spectroscopies, TGA, and their magnetic properties measured. All three compounds exhibit weak antiferromagnetic nearest neighbour interaction. A similar study on the known [FeIII(H2PO2)3] is also reported. Its magnetic susceptibility fits a model for a 1D-antiferromagnet with 2 J/k of 1.20(1) K and g of 2.019(2).