Using Steric Repulsion to Reduce the Coordination of Metal Centers in Adsorbed Transdibenzoporphyrins

Using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations, we have studied the adsorption of copper-tetraphenyltransdibenzoporphyrin (Cu-TPtdBP) and cobalt-tetraphenyltransdibenzoporphyrin (Co-TPtdBP) on Cu(111) at room temperature. At intermediate to high coverages, both molecules form the same structure on the surface, consisting of molecular rows, held together by T-type interactions between isoindole groups and phenyl rings of adjacent molecules. However, although the cobalt metal center of Co-TPtdBP in the adsorbed structure remains coordinated to its four surrounding nitrogen atoms, the central copper atom of Cu-TPtdBP loses its coordination to the two nitrogen atoms of the isoindole groups. Both the central copper atom of the molecule and the nitrogen atoms of the isoindole groups compensate for this by forming new bonds with the copper atoms in the Cu(111) surface. This is an example of a functional group that, through steric repulsion, distorts the adsorbed molecule, not only creating T-type interactions between adjacent molecules but also breaking chemical bonds to the metal center.