STM studies on monolayers of [Co(L)(4)]A(8) metallogrids on graphite

Self-assembled tetranuclear complexes of metallogrid type [Co-4(L-4)](PF6), R-1 = CH3, R-2 = H (compound 1) and [Co-4(L-4)](AsF6), R-1 = H, R-2 = CH3 (compound 2), L = 4,6-bis(6(11)R(1)-2(1),2(1)-bipyrid-6-yl)-2-R-2-pyrimidin e were adsorbed onto highly oriented pyrolitic graphite and studied by STM. Monodomains of a regularly packed layer of adsorbed molecules with areas u p to 0.5 mu m(2) were observed. Sample 1 showed a molecular pattern with ne arly orthogonal periodicities of 1.35 nm x 2.6 nm consisted with the size o f the 2 X 2 Co-grid oriented normally to the surface. A periodicity of 2.5 nm X 2.4 nm was found for complex 2 consistent with orientation of the grid parallel to the surface. Holes in the monolayer, which were formed by remo val of a particular complex by STM, were observed to diffuse along the surf ace with a diffusion coefficient of D = 5.2 X 10(-16) cm(2)/s. The free ene rgy of the diffusion activation were found to be Delta F-d = 730 meV. (C) 1 999 Published by Elsevier Science B.V. All rights reserved.