A N-14 nuclear quadrupole resonance study of phase transitions and molecular dynamics in hydrogen bonded organic antiferroelectrics 55DMBP-H(2)ca and 1,5-NPD-H(2)ca

作者：Seliger Janez^*; Zagar Veselko; Asaji Tetsuo; Gotoh Kazuma; Ishida Hiroyuki

来源：Physical Chemistry Chemical Physics, 2011, 13(20): 9165-9172.

DOI：10.1039/c0cp02873h

The temperature dependence of the N-14 NQR frequencies has been measured in antiferroelectric and paraelectric 55DMBP-H(2)ca and 1,5-NPD-H(2)ca. In both compounds we observe two non-equivalent nitrogen positions (N+-H center dot center dot center dot O- and N center dot center dot center dot H-O) in the antiferroelectric phase. The two nitrogen positions become equivalent (N center dot center dot center dot H center dot center dot center dot 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-H(2)ca by the H-1 and N-14 spin-lattice relaxation. An analysis of the spin-lattice relaxation data suggests a slow exchange between two non-planar conformations of the bipyridine molecule.

• 出版日期2011