| Ground state structures have been found using the density functional theory method PBE0/Def2-TZVPP//PBE0/Def2-SVP for the cis and trans isomers of platinum-metal-directed selfassemblies of four pyridine or acetylene terminated rods and four Pt(PR3)2 centers. The favored geometries are determined by a competition between ring strain and electronic strain at the Pt centers. The former generally grows and the latter decreases as the number of trans-Pt centers is augmented. For cationic complexes containing two bipyridyl and two biphenyl rods, with a +1 charge on each Pt center, a puckered structure with all four Pt centers cis is found to be 37.6 kcal/mol lower in energy than the isomer with all four Pt centers trans. For neutral complexes with four biphenyl rods and neutral Pt centers, the highly ring-strained planar, circular all-trans isomer lies 17.2 kcal/mol below the square-shaped all-cis isomer. |
