Racemic cobalt phosphonates incorporating flexible bis(imidazole) co-ligands

By incorporating flexible bis(imidazol-1-ylmethyl)benzene (bix) co-ligands, four new racemic cobalt phosphonates with formulae Co-3(3-ppap)(2)(1,4-bix)(2)(H2O)(4)center dot 4H(2)O (1), Co-3(3-ppap)(2)(1,3-bix)(2)(H2O)(4)center dot 5H(2)O (2), Co-3(3-ppap)(2)(1,2-bix)(2)(H2O)(4)center dot 4H(2)O (3) and Co-3(ppa)(2)(1,2-bix)(2)center dot 4H(2)O (4) are isolated, where 3-ppapH(3) represents 3-phenyl-3-((phosphonomethyl)amino) propanoic acid and ppaH(3) is 2-phenyl-2-(phosphonomethylamino) acetic acid. Compounds 1-3 crystallize in the monoclinic space group P2(1)/c and show two-dimensional structures in which the Co-3(3-ppap)(2) chains are bridged by 1,4-bix, 1,3-bix and 1,2-bix ligands in trans-modes, respectively. Within the chain, a racemic dimer of Co-2(3-ppap)(2)(2-) is found, where the Co atoms are doubly bridged by O-P-O units from the (S)-and (R)-3-ppap3-ligands. The dimers are connected by another crystallographically independent Co atom through O-P-O linkages to form an infinite racemic chain. The packing modes of the layers in 1-3 are quite different, however, which are ABAB in the cases of 1 and 3 while ABCDABCD in the case of 2, attributed to the positional isomerism of the bix co-ligands. Compound 4 displays a chain structure in which the 1,2-bix bridges the Co atoms in cis-mode within the chain. Magnetic properties are investigated for all compounds.