Cesium hydrogen sulphate CsHS04 and cesium hydrogen selenate CsHSe04 are pseudo-one-dimensional hydrogen bonded systems /1, 2/ with a structure resembling that of CsH2P04 in the paraelectric phase apart from the extra hydrogen in CsH2P04 /l/. At room temperature CsHS04 belongs t o the monoclinic space group P21/m with a = 7.304 8 , b = 5.810 8 , c = 5. 491 %, @ = = 101 .51° and two formula units per unit cell /1/ (Fig. 1). Separate chains of 0 -H --0 bonded SO4 groups run along the b-axis /l/. The length of the 0-H--0

The isotope effect of hydrogen motion in an organic ferroelectric, phenazine (Phz)-chloranilic acid (H 2 ca and D 2 ca for normal and deuterated compounds, respectively) co-crystal, was studied by 35 Cl nuclear quadrupole resonance (NQR). Besides a ferroelectric transition at T c = 253 K (303 K), a neutralto-ionic transition was found below 170 K (200 K) for Phz-H 2 ca (Phz-D 2 ca). 1 H-14 N nuclear quadrupole double resonance measurements were also made in order to study the temperature dependent electronic state of Phz-(H/D) 2 ca. 14 N NQR parameters suggested that donor orbital populations of the two nitrogen atoms in a phenazine molecule become nonequivalent (1.78 and 1.97) in the ferroelectric phase, while they are both equal to 1.89 in the paraelectric phase. In the ionic phase of Phz-D 2 ca, which was obtained by cooling below 188 K, they became 1.50 and 1.95, suggesting a proton transfer from D 2 ca to Phz.

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