Structure and energetics of Gd(III) interactions with water and ammonia

The geometry, binding energies, and isotropic hyperfine coupling constants of Gd(III)-ligand interactions in the Gd3+(H2O) and Gd3+(NH3) complexes hav e been determined by electronic structure methods. Polarized valence double -zeta and triple-zeta basis sets were developed to benchmark the properties of these complexes. Our calculations suggest that a correlated MP2 level c alculation and a triple-zeta basis set are essential for quantitative treat ments of the Gd(III)-ligand interaction. The combination of the uncorrelate d UHF method with a double-zeta basis set is unable to accurately describe the extreme polarization of the ligands in the presence of the trivalent Gd center. Spin polarization of the ligand results in the increase of alpha - electron density on Gd(III).