Two organic–inorganic hybrid halobismuthates(iii), (NH₂CHNH₂)₃[Bi₂Cl₉] (FBC) and (NH₂CHNH₂)₃[Bi₂Br₉] (FBB), have been prepared with their structures revealed by single-crystal X-ray diffraction at various temperatures.

The preparation of materials featuring more than one ferroelectric phase represents a promising strategy for controlling electrical properties arising from spontaneous polarization, since it offers an added advantage of temperature-dependent toggling between two different ferroelectric states. Here, we report on the discovery of a unique ferroelectric–ferroelectric transition in diisopropylammonium tetrabromocadmate (DPAC, (C₆H₁₆N)₂[CdBr₄]) with a T_c value of 244 K, which is continuous in nature. Both phases crystallize in the same polar orthorhombic space group, Iab2. The temperature-resolved second-harmonic-generation (SHG) measurements using 800 nm femtosecond laser pulses attest to the polar structure of DPAC on either side of the phase transition (PT). The dc conductivity parameters were estimated in both solid phases. The anionic substructure is in the form of [CdBr₄]^2– discrete complexes (0D), while in the voids of the structure, the diisopropylammonium cations are embedded. The ferroelectric properties of phases I and II have been confirmed by the reversible pyroelectric effect as well as by P–E loop investigations. On the basis of the dielectric responses, the molecular mechanism of the PT at 244 K has been postulated to be of mixed type with an indication of its displacive nature.

The crystal structure of [C(NH₂)₃]₃[Ho(ttha)]·3H₂O (H₆ttha=triethylenetetraaminehexaacetic acid) has been determined. The coordination environment of the Ho^III ion is composed of five carboxylate oxygen atoms and four nitrogen atoms. Electronic absorption spectra of a [C(NH₂)₃]₃[Ho(ttha)]·3H₂O single crystal were measured at room and liquid helium temperatures and compared with those of the Ho^III–ttha (1:1) complex in solution. The results suggest that a species of coordination geometry similar to that of the [Ho(N₄O₅)]³⁻ type found in the crystal exists predominantly in solution at pH>5. At lower pH values, as for other Ln^III–ttha complexes, coordination equilibria are observed.