Organoplatinum polymorphs with varying molecular conformation, intermolecular interaction, and luminescence

Two mononuclear organoplatinum complexes based on the 2,2'-dipyridylamino derivative ligands (2,2'dipyridylamino)phenyl triphenyl methane (dm) and (2,2'-dipyridylamino)phenyl triphenyl silane (dsi) with the formula PtPh2(dm) (1) and PtPh2(dsi) (2), respectively, have been synthesized. Both 1 and 2 have been found to form two polymorphs concomitantly: a colorless blue-luminescent form A (space group I4(1)/a) (1A and 2A) and a yellow nonluminescent form B (space group P2(1)/c) (1B and 2B). The crystal Structures of 1A, 1B, and 2A were determined by single-crystal X-ray diffraction analyses. The CPh3 group was found to display different conformations in the crystal lattices of 1A and 1B. Considerable variations in intermolecular interactions were also observed for the crystals of 1A and 1B. 2A was found to be isostructural to 1A. Spectroscopic study (UV-vis and luminescence) and molecular orbital calculations (Gaussian98) were performed to understand the color and luminescent differences between 1A and 1B. Intermolecular pi-pi stacking interactions between a phenyl of the CPh3 group and the pyridyl of the 2,2'-dipyridylamino group were found to be the most likely cause for the absence of emission in the crystals of 1B.