The temperature dependence of the 14N NQR frequencies has been measured in antiferroelectric and paraelectric 55DMBP-H2ca and 1,5-NPD-H2ca. In both compounds we observe two non-equivalent nitrogen positions (N+-H⋯O- and N⋯H-O) in the antiferroelectric phase. The two nitrogen positions become equivalent (N⋯H⋯O) in the paraelectric phase. The critical exponent of the local antiferroelectric order parameter has been determined from the NQR data. The principal values of the quadrupole coupling tensor correlate in both compounds. The correlation diagrams clearly show how a proton migrates from the antiferroelectric position towards the paraelectric position in the bifurcated hydrogen bond on increasing the temperature. A slow motion has been observed in 55DMBP-H2ca by the 1H and 14N spin-lattice relaxation. An analysis of the spin-lattice relaxation data suggests a slow exchange between two non-planar conformations of the bipyridine molecule.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry