Interaction of Cu atoms with ordered 2D oligopyridine networks

The effect of Cu deposition on pre-deposited ordered oligopyridine networks on HOPG was investigated by scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV) conditions. Deposition of small amounts of Cu and subsequent annealing results in the formation of a new hexagonal metal organic structure, coexisting with the previous quasiquadratic network (QQN) phase. In the new phase, the oligopyridines are dominantly linked by incorporated Cu centers. The high stability of the bonds between pyridyl nitrogen atoms and Cu-2 dimers, which is the structure determining element in the metal organic network, overcompensates the loss in C-H center dot center dot center dot N bridge interaction, which is the dominant interaction in the QQN phase. The Cu-2 mediated gain in intermolecular interaction energy provides the driving force for the Cu induced structural transition, from QQN phase to the hexagonal metal organic network structure. (C) 2007 Elsevier B.V. All rights reserved.