| The strength of a metal-ligand interaction depends upon a number of factors. Various properties of the metal such as its size, charge (or oxidation state), and valence electronic configuration strongly influence the binding interaction. Characteristics of the ligand such as the nature and number of donor atoms available for binding, and the molecular polarizability and dipole moment also influence the binding interaction. In addition, chelation and the extent of ligation are also important factors that control the geometry and strength of metal-ligand binding interactions. In the studies described here, the factors were probed by varying the metal ion, ligand, and extent of ligation.;The kinetic energy dependence of the collision-induced dissociation of a wide variety of metal-ligand complexes with Xe is studied using guided ion beam tandem mass spectrometry. The dominant dissociation processes observed for most complexes is simple collision-induced dissociation (CID) corresponding to endothermic loss of a single neutral ligand. In addition to simple CID to produce the metal ion and neutral ligand, activated dissociation pathways are also observed in several complexes. Sequential dissociation of additional ligands is also observed at elevated energies for most complexes containing more than one ligand. The metal ions examined in these studies include: Na +, Mg+, Al+, Ca+, Sc +, Ti+, V+, Cr+, Mn +, Fe+, Co+, Ni+, Cu +, and Zn+. The N-donor ligands investigated include: imidazole, pyridine, 4,4-dipyridyl, 2,2-dipyridyl, and 1,10-phenanthroline. The extent of ligation was varied between one and four ligands.;The cross section thresholds for the primary dissociation pathways are interpreted to yield 0 and 298 K BDEs after accounting for the effects of multiple ion-neutral collisions, the kinetic and internal energy distributions of the reactants, and dissociation lifetimes. Density functional theory calculations at the B3LYP/6-31G* level are performed to obtain model structures, vibrational frequencies, and rotational constants for the neutral ligands and metal-ligand complexes. The relative stabilities of the various conformations of these neutral ligands and metal-ligand complexes as well as theoretical metal-ligand BDEs are determined from single point energy calculations at the B3LYP/6-311+G(2d,2p) level of theory using B3LYP/6-31G* optimized geometries. In general, reasonably good agreement between the measured and computed metal-ligand BDEs is found for most complexes. However, in some cases theory was unable to accurately describe the strength of binding. Therefore, in limited cases several additional levels of theory were investigated to assess the accuracy of the calculations. The nature of the binding interactions in metal-ligand complexes is examined via natural bond orbital (NBO) analyses. |
