title: Inter-hydrogen bond coupling in crystals with molecular chains in their lattices investigated by polarized IR spectroscopy: 4-Bromo-3,5-dimethylpyrazole and 3,4-dimethoxyphenylacetic acid.
abstract: We report the results of the experimental and theoretical studies of the polarized IR crystalline spectra of 4-bromo-3,5-dimethylpyrazole (4Br35DMPz) and 3,4-dimethoxyphenylacetic acid (34DMPAA) as well as the spectra of their deuterium-bonded analogues. The results of model calculations of the temperature impact exerted on to the band shapes measured in the X-H- and X-D bond stretching vibration regions, performed on the basis of the "strong-coupling" model, are also shown. These studies confirm a direct relationship between the spectral properties in IR and the electronic structure of the associating molecules in the crystals. Two different competing exciton coupling mechanisms involving hydrogen bonds, the "tail-to-head" (TH) in 4Br35DMPz and the "side-to-side" coupling in 34DMPAA, were recognized. The molecular electronic structure determines the relative contribution of each individual vibrational exciton coupling mechanism in the spectra generation. It also strongly influences the temperature-induced evolution of the Davydov-splitting effects in the crystalline spectra. Dynamical co-operative interactions responsible for a non-random distribution of protons and deuterons in the crystal hydrogen bonds can also be identified in the investigated systems.
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.
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: Anna
authors.initials: A
authors.lastname: Polasz
mesh_terms: D003460:Crystallization; D003903:Deuterium / Q000737:chemistry; D054879:Halogenation; D006860:Hydrogen Bonding; D008958:Models, Molecular; D010648:Phenylacetates / Q000737:chemistry*; D011720:Pyrazoles / Q000737:chemistry*; D013055:Spectrophotometry, Infrared / Q000379:methods; D013696:Temperature
chemical_list: D010648:Phenylacetates; D011720:Pyrazoles; D003903:Deuterium; C027635:3,5-dimethylpyrazole
keywords: Dynamical co-operative interactions; Hydrogen bond; Inter-hydrogen bond coupling; Polarized IR spectra; Temperature effects