Oxalate- and Squarate-Biimidazole Supramolecular Synthons: Hydrogen-Bonded Networks Based on [Co(H2biimidazole)3]3+

The utility of R-2(2)(9) biimidazole-carboxylate, R-2(2)(10) biimidazole-oxalate/squarate and R-2(2) (9) biimidazole-(tris-oxalate) synthons is considered for crystal engineering of hydrogen-bonded networks based on [Co-III(H(2)biim)(3)](3+) cations (H(2)biim = 2,2-biimidazole) and oxalate, squarate or [M-III(C2O4)(3-) anions. Syntheses and crystal structures are described for [Co-III(H(2)biim)(3)](3-) [M-III(C2O4)(3)]center dot 2H(2)O (M = Cr, 1; M = Co, 2), [Co-III(H(2)biim)(3)](HC4O4)(3)center dot 2H(2)O, 3, and [Co-III(H(2)biim)(3)](C2O4)Cl center dot 5.5H(2)O, 4. Compounds 1 and 2 are isostructural and comprise [Co(H(2)biim)(3)](3+) cations bridged by [M(oxalate)(3)](3-) anions in two directions and water molecules in the third direction to give a 3D H-bonded network. Both outer and inner 0 atoms of the coordinated oxalate ions act as H-bond acceptors, forming motifs closely related to the anticipated R-2(2)(9) biimidazole-(tris-oxalate) synthon. Compound 3 contains a more complex H-bond pattern in 3D, built from the intended R-2(2)(10) biimidazole-squarate synthon and additional H-bonds between protonated squarate molecules and water molecules. The structure of compound 4 (obtained with synchrotron radiation) contains layers in which stacked pairs of oxalate anions bridge between [Co-III(H(2)biim)(3)](3+) cations to form a dense 2D kgd-net, separated by layers of disordered chloride anions and H-bonded water molecules.