Organic-inorganic Bi(III)- and Sb(III)-based hybrids. Structural and physicochemical versatility in functional materials design

Phase transition (PT) materials whose physical properties can be controlled by external stimuli have continuously attracted considerable interest due to their wide-range optoelectronic applications.[1] The ferroelectric PTs are of importance as regards the design of thermo-sensitive multifunctional switching materials because they are often accompanied by multiple switchable physical properties, e.g. piezoelectricity, pyroelectricity, dielectric constant as well as second harmonic generation. As one class of molecular materials taking advantage of lightweight and mechanical flexibility, the organic-inorganic hybrid ferroelectrics are currently of particular interest, due to the designable and tunable characteristics of their organic and inorganic components, for exploring ferroelectric-based multifunctional materials such as multiferroics, semiconductors and photovoltaics.[2] A considerable effort has been made so far to understand the switchable molecular dynamics of polar organic cations confined in various polymeric coordination hosts. However, due to the lack of in-depth knowledge of the relationship between PT and a crystal structure, a rational design of molecular ferroelectrics still represents a great challenge, especially for hybrid molecular ferroelectrics based on polar organic cations.

As regards halobismuthtates(III) and haloantimonates(III), the polar (ferroelectric) properties usually come from the organic networks, and the long-range order of dipolar organic cations is a source of the spontaneous polarization. Importantly, the ‘order-disorder’ transformations of the organic cations are usually conjugated with the distortion of the inorganic part. Nevertheless, the ‘displacive’-type of the molecular mechanism of PT is often shielded by dominating ‘order-disorder’ contribution.[3]

[1] X.-B. Han, et al., CrystEngComm, 2022, 24, 1507
[2] L. Schmidt-Mende et al., APL Mater. 2021, 9, 109202
[3] R. Jakubas et al., Inorg. Chem. Front., 2020, 7, 2107