Comparative study on two novel nine-coordinated supramolecular compounds of cerium(III) and yttrium(III): Solid and solution states studies

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The solution chemistry and solid-state structures of two new metal–organic compounds of Ce(III) and Y(III) atoms, (4-apyH)3[Ce(pydc)3]·4H2O, 1, and (4-apyH)3[Y(pydc)3]·4H2O, 2 (pydc=pyridine-2,6-dicarboxylate, 4-apy=4-aminopyridine), have been investigated. These compounds were obtained via proton transfer methodology. On the basis of crystallographic data, each MIII is coordinated in a distorted tricapped trigonal prism geometry. Furthermore, [M(pydc)3]3− anions and (4-apyH)+ moieties form a three-dimensional structure by a variety of noncovalent interactions such as extensive O–H⋯O, N–H⋯O and C–H⋯O hydrogen bonds, ion pairing, C–H⋯π, π–π and carbonyl stacking interactions. The equilibrium constants for the binary pydc-4-apy proton transfer system, the stoichiometry and stability of complexation of this system with Ce3+ and Y3+ ions in aqueous solution were investigated by potentiometric pH titration method. In each case, the stoichiometry of the dominant metal complex species in solution was compared to that obtained from the crystal structure.