Energy-Resolved Collision-Induced Dissociation Studies of 2,2′-Bipyridine Complexes of the Late First-Row Divalent Transition-Metal Cations: Determination of the Third-Sequential Binding Energies



The third-sequential binding energies of the late first-row divalent transition-metal cations with 2,2′-bipyridine (Bpy) are determined using guided-ion-beam tandem mass spectrometry (GIBMS) techniques. The metal cations investigated include the late first-row divalent transition-metal cations, Fe2+, Co2+, Ni2+, Cu2+, and Zn2+. The kinetic-energy-dependent cross sections for collision-induced dissociation (CID) of the M2+(Bpy)3 complexes are analyzed to extract absolute 0 and 298 K bond dissociation energies (BDEs) for the loss of an intact Bpy ligand. Theoretical electronic structure calculations at the B3LYP, BHandHLYP, and M06 levels of theory are performed to determine stable geometries and sequential BDEs of the M2+(Bpy)x complexes (x=1–3). BDEs computed using the M06 functional are the largest, BHandHLYP values are intermediate, whereas B3LYP produces the smallest values. Very good agreement between the B3LYP theoretically calculated and threshold collision-induced dissociation experimentally determined BDEs is found, which suggests that the B3LYP functional is capable of accurately describing the binding in these M2+(Bpy)3 complexes. Periodic trends in the binding of the M2+(Bpy)x complexes are examined and compared to the analogous complexes with 1,10-phenanthroline (Phen), M2+(Phen)x. Comparisons are also made to the analogous Bpy complexes, M+(Bpy)x, with the late first-row monovalent transition-metal cations, Co+, Ni+, Cu+, and Zn+ investigated previously.