Dinuclear Metal-Mediated Homo Base Pairs with Metallophilic Interactions: Theoretical Studies of GM (M = Cu, Ag, and Au) Ions.

Dinuclear metal-mediated homo base pairs are interesting clusters with highly symmetric structures and significant stabilities. The geometric and electronic structures of GM (G = Guanine, M = Cu, Ag or Au) cluster ions were studied with quantum chemical calculations. The lowest-energy isomers of GM cluster ions have C symmetries with an approximately antiparallel alignment of two sets of N-M∙∙∙O groups being formed in the planar structures. The M-M distances are shorter than the sum of van der Waals radii of corresponding two homo coinage metal atoms, showing that metallophilic interactions significantly exist in these complexes. They have the large HOMO-LUMO gaps of about 5.80 eV at the DFT level and the bond dissociation energies of more than 5.60 eV at the DFT/B3LYP level, indicating that these cluster dications are highly stable. The second lowest-energy isomers stabilized by an approximately parallel alignment of one set of O-M-O group and one set of N-M-N group are found to be close to the lowest-energy isomers in energy. The barrier between the two isomers of GM cluster ions is significantly large, also showing that these lowest-energy isomers are very stable.