Calcium-ligand interactions

The compound [Ca(hfac)2(H20)2]2153 (Fig. 38) is a centrosymmetric dimer in the solid state, while the analogous barium complex, [Ba(hfac)2 (H20)]x,153 exists as a polymer. Both compounds have M-F interactions similar to those described for [Ba2(hfac)4(Et20)L The smaller size of calcium is probably responsible for the structural differences between these two water adducts. The volatility of these fluorinated complexes is certainly decreased by the M-F interactions, as well as by the overall oligomeric structure of the compounds. What relationship metal ligand interactions of this type play in the incorporation of BaF2 in films prepared from these compounds has not yet been elucidated. Interestingly, no base-free fluorinated /3-diketonate compounds have been structurally characterized. 

For a review of adducts with calcium salts, see W. J. Cook and C. E. Bugg, in B. Pullman and N. Goldblum (Eds.), Metal-Ligand Interactions in Organic Chemistry and Biochemistry, Part 2, Reidel Publishing Company, Dordrecht (Holland), 1977, pp. 231-256. 

The three commonly observed modes of calcium carboxylate ligation. (A) The unidentate mode, in which the calcium ion interacts with only one of the two carboxylate oxygens. (B) The bidentate mode, in which the calcium ion is chelated by both oxygen atoms. (C) The a-mode, in which the calcium ion is chelated by one carboxylate oxygen, and another ligand is attached to the a-carbon. Adapted from Reference 11. 

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