Observation of intermolecular N-I interaction during the growth of a 4-cyano-4′-iodobiphenyl molecular crystal on GeS(001)

The electronic and atomic structures of 4-cyano-4′-iodobiphenyl (CIB) during the growth of a molecular crystal on a GeS(001) substrate were studied by ultraviolet photoemission spectroscopy (UPS), atomic force microscopy (AFM), and extended X-ray absorption fine structure (EXAFS) spectroscopy. AFM images suggest that the CIB molecule grows as a microcrystal at a nominal thickness of 80 Å. The microcrystal grows with the crystal plane parallel to the surface and isotropic crystal axis orientation. EXAFS analysis suggests that a CIB crystal forms by strong N···I interaction, called halogen bonding. The formation of the intermolecular N···I bond was demonstrated by EXAFS analyses in which the N-I distance was determined to be 3.29 Å. An upward shift of the highest occupied molecular orbital level was observed by UPS and can be attributed to the aggregation of CIB molecules caused by halogen bonding.