Syntheses, Crystal Structures, and Photophysical Properties of Heteronuclear Zinc(II)/Cadmium(II)-Lanthanide(III) Coordination Complexes based on Benzoic Acid

The heteronuclear d- f coordination complexes [ Er2Zn2(C6H5COO) 10( phen) 2] ( 1), [ Ho2Zn2( C6H5COO) 10( phen)(2)] ( 2), [ Pr3Zn6( C6H5COO) 21( phen) 3] ( 3), [ ErCd( C6H5COO) 5( phen) center dot H2O] ( 4), [ Ho2Cd3( C6H5COO) 12( phen)(2)] ( 5), [ EuCd2( C6H5COO)(7)( phen)(2)] ( 6) ( C6H5COOH = benzoic acid; phen = 1,10- phenanthroline) were synthesized by hydrothermal methods, and their structures were studied by single- crystal X- ray diffraction. Complexes 1, 2, 4, and 5 crystallize in the triclinic space group P1 and complexes 3 and 6 in the monoclinic space group C2/ c. The room temperature IR, UV/ Vis/ NIR ab- sorption, and emission spectra of the six complexes were determined and assigned. In the visible and NIR regions, the emission spectra of complexes show characteristic bands of corresponding LnIII ions, which are attributed to the sensitization from the d block ( Zn/ Cd- ligand section) and ligands. In comparison with isolated Ln(III) ions, the NIR emission bands of complexes 1- 5 exhibit shifting, broadening and splitting, which are also present in their UV/ Vis/ NIR absorption spectra. Thus, the two spectra of complexes can evidence each other.