ACS PRF | ACS
All e-Annual Reports
45243-AC3
Polymorphs and Polymorphic Transformations that Alter Chemical Bonding
This proposal is designed to examine the structures and inter-conversion between polymorphs of transition metal complexes. The project emphasizes compounds where significant changes in chemical interactions between molecules produce marked spectral differences between the polymorphs. Two-coordinate d10 (particularly Au(I)) and four-coordinate d8 transition metal complexes display metallophilic interactions, which are susceptible to producing significant differences that can depend upon how the materials are crystallized. Hence our preliminary studies have focused on complexes of this type. We are studying the effects of organic vapors, organic liquids, mechanical stress, and temperature on individual polymorphs
Bonati and Ugo (Bonati, F.; Ugo, R. J. Organometal. Chem. 1967, 7, 167-180) reported that dicarbonyl[2(p-tolylimino)penten-3-olato-4]iridium(I) formed two apparent polymorphs when crystallized from hexane. We have re-examined this situation and found that 4 different polymorphic phases of the solid can be prepared. We have determined the structures of each polymorph by X-ray diffraction at 298 and 90 K. The polymorphs are luminescent at 90 K, and the luminescent behavior has been correlated with the structural differences in each of the phases. We have carefully examined the methods of obtaining each polymorph and have examined the possibility of inter-conversions among these polymorphs. Three of the phases are related thermally and one reversible transformation between phases has been identified. A manuscript describing these results is in the final stages of preparation and will be submitted for publication within the next six weeks.
Vallarino and Sheargold (Vallarino, L. M.; Sheargold, S. W. Inorg. Chim. Acta 1979, 36, 243-252.) noted that complexes of the type (amine)RhI(CO)2X (X = Cl, Br, I) crystallize to form solids with a remarkable variety of colors: yellow, violet, green, red, blue, and bronze. We have crystallized a number of complexes of this type along with their iridium(I) analogs. We have found a new structural motif in these materials. These planar molecules stack to form metallophilic interactions along the stacking direction, and these interactions are augmented by strong intermolecular hydrogen bonding between the N-H group on one molecule and the halide ligand on an adjacent molecule. Vallarino and Sheargold reported that yellow and purple forms of (2-naphthylamine)RhI(CO)2Cl could be differentiated on the basis of their color and infrared spectra. No crystallographic data on these forms was reported. We suspected that these forms represented different polymorphs. However, we have not been able to produce distinct yellow and purple forms. In our hands only the yellow form has been observed. We have determined its structure crystallographically and shown that it also crystallizes in stacks with metallophillic interactions and hydrogen bonding running parallel to the stacking direction. Work on identifying polymorphs of these planar complexes continues.
A review of the remarkable luminescent properties of gold(I) complexes, with an emphasis on those with relatively simple ligands has been written and published. The review was not designed to be comprehensive but focused on particular topics that show the range of factors that can alter the luminescence that arises from relatively simple, two-coordinate complexes. Particular emphasis was place on demonstrating cases where the spectroscopic properties of two-coordinate gold(I) complexes displayed spectroscopic features that are sensitive to the solid-state environment.
