Racemic metal phosphonates based on 2-phenyl-2-(phosphonomethylamino)acetate

The first examples of metal phosphonates based on 2-phenyl-2-(phosphonomethylamino)acetic acid (ppaH3) are reported, namely, Co3(ppa)2(4,4′-bpy)2(H2O)4·2H2O (1) and Ni4(ppaH)4(4,4′-bpy)2(H2O)2 (2). Compound 1 shows a three-dimensional framework structure in which the Co3(ppa)2 chains are cross-linked by 4,4′-bpy ligands. Within the chain, the equivalent Co2 atoms are doubly bridged by the O–P–O units from the R- and S-ppa(3−) ligands forming a racemic dimer of Co2(ppa)2. The dimers are connected by the Co1 atoms through O–P–O units to form an infinite racemic chain. Compound 2 displays a layer structure, where chains of Ni2(ppaH)2 are fused together by 4,4′-bpy. Within the chain, dimers of equivalent Ni atoms with O–P–O linkages are again observed. Unlike compound 1, however, the opposite handedness dimers are linked via O–C–O bridges into an infinite racemic chain. Magnetic studies reveal that dominant antiferromagnetic interactions are mediated between the magnetic centers in both cases.