Experimental and theoretical studies of binding interactions in divalent transition metal cation-N-donor ligand complexes: Structures, sequential bond dissociation energies, mechanisms and energetics of collision-induced dissociation

The thesis research described here involves a series of experiments that have been designed to probe the influence of the electronic structure of the metal cation, the nature and number of ligands, as well as the effects of chelation and steric interactions on the geometry and binding strength of transition metal cation-ligand complexes. The experimental studies make use of energy-resolved collision-induced dissociation (CID) techniques that are carried out in a custom-built guided ion beam tandem mass spectrometer (GIBMS) to probe the structures, energetics, and fragmentation behavior of the complexes of interest. Electronic structure theory calculations including several density functional theory methods are employed to determine stable low-energy structures of the M2+(N-L)x complexes and the relevant species associated with their CID behavior. The five late first-row transition metal cations in their 2+ oxidation states, Fe2+, Co2+, Ni2+, Cu 2+, and Zn2+, are included in this work. The N-donor ligands (N-L) investigated here include pyridine (Pyr), a monodentate ligand, and two pyridine based bidentate ligands, 2,2-bipyridine (Bpy), and 1,10-phenanthroline (Phen). The structures and energetics of these complexes are investigated theoretically, while the CID behavior is investigated experimentally.;In Chapters 3 and 4, we found that the dominant dissociation pathway for all M2+(Phen)3 and M2+(Bpy) 3 complexes is loss of an intact Phen and Bpy ligand, respectively. In both cases, the BDEs computed using the M06 theory are found to be the largest, BHandHYP values are intermediate, whereas B3LYP produced the smallest values. Very good agreement between the B3LYP theoretically calculated and TCID experimentally determined BDEs was found for both M2+Phen) 3 and M2+(Bpy)3 complexes, suggesting that the B3LYP functional is capable of accurately describing the binding in these complexes. The sequential BDEs of M2+(Phen)x and M2+(Bpy)x complexes are observed to decrease monotonically with increasing ligation for all five metal cations regardless of which theory is employed.;Chapter 5 examines the ground-state structures and sequential binding energies of the M2+(Pyr)x complexes, x = 1--6 by density functional theory methods. Structures of the Ca2+(Pyr)x complexes are compared to those of the M2+(Pyr)x complexes to Fe2+, Co2+, Ni2+, Cu 2+, and Zn2+ to further assess the effects of the d-orbital occupation of the preferred binding geometries. The B3LYP, BHandHLYP, and M06 levels of theory yield very similar geometries for the analogous M 2+(Pyr)x complexes. The overall trends in the sequential BDEs for all five metal cations at all three levels of theory examined are highly parallel, and are determined by a balance of the effects of the valence electronic configuration and hybridization of the metal cation, but are also influenced by ligand-ligand repulsive interactions.;Preliminary studies covered in Appendices D and E are inter-related and describe the results of mapping the mechanisms and energetics of fragmentation pathways of M2+Phen)2 and M2+(Bpy) 2 complexes, respectively. Four types of reaction pathways are observed in competition in all the M2+(Phen)2 and M 2+(Bpy)2 complexes including ETCF, PTCF, simple CID, and dehydrogenation. For all the M2+(Phen)2 and M 2+(Bpy)2 complexes, severe overlap of the products separated by 1 Da originating from the ETCF and PTCF pathways is observed because the experiments were performed under low-resolution conditions. Preliminary data analysis of the cross sections is performed for the ETCF and simple CID pathways, without consideration of the PTCF pathway for all the M2+Phen) 2 and M2+(Bpy)2 complexes. As a result, the activation energies and bond dissociation energies extracted are only approximate. (Abstract shortened by UMI.).