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Water-presence dependent switchable ferroelectricity was discovered in the hybrid organic–inorganic zinc oxalate 1D coordination polymer (DABCOH2)[Zn(C2O4)2]·3H2O (DZnOH, where DABCOH2: diprotonated 1.4-diazoniabicyclo[2.2.2]octane). The compound undergoes a reversible para–ferroelectric phase transition at 207 K from room temperature centrosymmetric phase I (space group P21/n) to low-temperature non-centrosymmetric phase II (space group P21). The microscopic mechanism of the phase transition is directly associated with the reconstruction of the hydrogen-bond network. On heating, the crystals exhibit a reversible single-crystal to single-crystal transformation concerned with the removal of all water molecules giving anhydrous DABCO zinc oxalate (DABCOH2)[Zn(C2O4)2] (DZnO). The dehydrated compound does not show ferroelectric properties. [ABSTRACT FROM AUTHOR]

Abstract: The structure of [C3N2H5]4[Bi2Br10]·2H2O, (PBB) was determined by single crystal X-ray diffraction at 100K. It crystallizes in the monoclinic space group C2/m, with a =12.992(4)Å, b =16.326(5)Å, c =8.255(3)Å, β =108.56°(3), V =1659.9(9)Å3 and Z =2. The structure consists of discrete binuclear [Bi2Br10]4− anions, ordered pyrazolium cations and water molecules. The crystal packing is governed by strong N–H⋯O and weak O–H⋯Br hydrogen bonds. A sequence of structural phase transitions in PBB was established on the basis of differential scanning calorimetry and dilatometric studies. Two reversible first-order phase transitions were found: (I→II) at 381/371K (on heating/cooling) and (II→III) at 348/338K. Dielectric response near both phase transitions is characteristic of crystals with the “plastic-like” phases. Over the phase III a low frequency dielectric relaxator is disclosed. The possible molecular motions in the PBB compound are characterized by the 1H NMR studies. The infrared spectra of polycrystalline compound in the temperature range 300–380K are reported for the region 4000–400cm−1. The observed spectral changes through the structural phase transition III→II are attributed to an onset of motion both of the pyrazolium cations and water molecules. [Copyright &y& Elsevier]

Abstract: The crystal structures of [C3H4NS]6[M 4Cl18]·2H2O (M =Sb, Bi) consist of three nonequivalent thiazolium cations and discrete centrosymmetric anions [M 4Cl18]6−. The title compounds appear to be isomorphous and crystallize in the triclinic space group, (at 100K). One of three thiazolium cations was found to be disordered (two-site model). [C3H4NS]+ cations are hydrogen bonded to [M 4Cl18]6− units and water molecules. The water molecules (Ow) via the O–H…Cl hydrogen bonds are involved in the one-dimensional polymeric chains, which extend along the c-axis. The dielectric dispersion studies on two thiazolium analogs in the audio-frequency region disclosed complex relaxation processes. The dielectric response indicates the presence of two independent relaxators, which are characterized by polydispersive nature. The relaxation processes taking place in the both studied crystals are due to the motion of dipolar thiazolium cations. [Copyright &y& Elsevier]