Hierarchical Assembly and Reticulation of Two-Dimensional Mn- and Ni-TCNQ(x) (x=1, 2,4) Coordination Structures on a Metal Surface
We report a scanning tunneling microscopy (STM) investigation of the self-assembly of two-dimensional metal-organic coordination networks comprised of Mn or Ni atoms (M) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) molecules on a Ag(100) surface. The growth is dominated by the coupling of the cyano ligands to the substrate, and this interaction is reduced by lateral coordination of the molecules to metal adatoms. Initially mononuclear M-TCNQ(4) complexes form at room temperature, which hierarchically assemble into reticulated M-TCNQ(2) networks at sufficiently high metal concentrations. M-TCNQ(1) networks with fully Coordinated molecules can be obtained at elevated substrate temperatures and sufficient metal concentration. A commensurate a and an incommensurate beta phase can be distinguished that are unrelated to the antedecent M-TCNQ(4) complexes. The coordination of the cyano groups to metal adatoms alters the balance between lateral interactions and coupling of the molecules to the substrate. This effect is accompanied by distinct changes in the apparent heights of metal centers in the STM data indicating changes in their electronic configuration.