Volume 89 Issue 45 | p. 24 | Concentrates
Issue Date: November 7, 2011

Molecular Symmetry Sets Surface Disco Dance Moves

Department: Science & Technology
Keywords: molecular symmetry, NaCl
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Copper (II) tetraazphthalocyanine, shown with copper in gold, nitrogen in blue, carbon in gray, and hydrogen in white. Isomers of a Cu(II) complex, depicted in these symmetry representations, move differently when adsorbed onto a NaCl film; blue squares indicate outer nitrogen atoms and red squares indicate rotation axes.
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Copper (II) tetraazphthalocyanine, shown with copper in gold, nitrogen in blue, carbon in gray, and hydrogen in white. Isomers of a Cu(II) complex, depicted in these symmetry representations, move differently when adsorbed onto a NaCl film; blue squares indicate outer nitrogen atoms and red squares indicate rotation axes.
Videos of different isomers of Cu(II) tetraazaphthalocyanine show how they move differently on an NaCl film.
Credit: Phys. Rev. Lett.

The symmetry of a molecule can determine how it moves after it’s adsorbed on a surface, according to researchers at the University of Regensburg, in Germany (Phys. Rev. Lett., DOI: 10.1103
/physrevlett.107.186103
). Ingmar Swart, Jascha Repp, and colleagues studied the vibronically induced movement of copper(II) tetraazaphthalocyanine molecules deposited on a NaCl film. Varying the position of the nitrogen atoms on the outer edges of the phthalocyanine ring system produces isomers of varying symmetry that behave differently on the NaCl surface. The C4 symmetry isomer has a fourfold rotational axis and moves across the NaCl film in two dimensions, landing mostly on chlorine atoms without rotating. The Cs isomer has a mirror plane bisecting the molecule and also moves in two dimensions, but it lands on sodium atoms and can rotate by 90° so that its mirror plane aligns with those of the surface. The asymmetric C1 isomer moves in two dimensions as well, but it has no apparent preferred absorption site or orientation. And the C2 isomer, which has a twofold rotational axis, moves back and forth along a straight line above NaCl bridge sites, without rotating. The researchers suggest that the different diffusion patterns arise from polar interactions between the molecule’s nitrogen atoms and the NaCl substrate.

 
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