title: Inter-hydrogen bond coupling in crystals of 3-phenylpyrazole polymorphs investigated by polarized IR spectroscopy.
abstract: The remarkably strong differences in the fine structure patterns of the νN-H and νN-D bands, temperature and H/D isotopic effects in crystals of two 3-phenylpyrazole (3PhPz) polymorphs, with tetrameric and hexameric hydrogen bond aggregates, were examined by polarized IR spectroscopy, aided by the calculations utilizing the "strong-coupling" model. Experimental and theoretical approaches have suggested that the anti-co-operativity of hydrogen bonds is the main factor responsible for the differences in the spectral properties of both polymorphs. This interaction affects hydrogen-bond geometry of the associates constituting the lattices and in consequence decides about the relative contribution of two different exciton coupling mechanism, "through-space" (SS) and "tail-to-head" (TH), in the spectra generation. The relative contribution of each individual exciton coupling mechanism in the spectra generation is temperature-dependent. In tetramers the TH coupling mechanism dominates at low temperatures, whereas the role of the SS mechanism increases at higher temperatures. For the hexamers the SS mechanism dominates in the wide temperature range. The two types of 3PhPz associates exhibit two different ways of occurring of the H/D isotopic recognition in the crystal hydrogen bonds. In the tetrameric polymorph identical hydrogen isotope atoms exist in entire hydrogen-bonded cycle of 3PhPz. In the case of 3PhPz hexamers, the H/D isotopic recognition mechanism involves pairs of the closely-spaced hydrogen bonds in a cycle.
authors.affiliation: Institute of Chemistry, University of Silesia, 9 Szkolna Street, Pl-40-006 Katowice, Poland. Electronic address: barbara.hachula@us.edu.pl.
authors.forename: Barbara
authors.initials: B
authors.lastname: Hachuła
authors.affiliation: Institute of Chemistry, University of Silesia, 9 Szkolna Street, Pl-40-006 Katowice, Poland. Electronic address: flakus@ich.us.edu.pl.
authors.forename: Henryk T
authors.initials: HT
authors.lastname: Flakus
authors.affiliation: Institute of Chemistry, University of Silesia, 9 Szkolna Street, Pl-40-006 Katowice, Poland.
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Garbacz
authors.affiliation: Department of Physical Chemistry and Technology of Polymers, Faculty of Chemistry, Silesian University of Technology, 9 Marcina Strzody Street, Pl-44-100 Gliwice, Poland.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Stolarczyk
mesh_terms: D003460:Crystallization; D006859:Hydrogen / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D011720:Pyrazoles / Q000737:chemistry*; D013055:Spectrophotometry, Infrared / Q000379:methods
chemical_list: D011720:Pyrazoles; D006859:Hydrogen
keywords: Anti-co-operativity; Hydrogen bond; Molecular crystals; Polarized IR spectroscopy; Polymorphism