Molecular ferroelectrics based on bicyclic amine cations and chlorocobaltate(II) anions

Solid–solid phase transition compounds with electric, magnetic, and thermally switchable states usually provide an effective strategy for the design of functional materials such as ferroelectric materials, nonlinear-optical switches, and switchable dielectric devices. Among these properties, ferroelectric behaviour is particularly desirable because it is possible to switch rapidly between different states by an external electric field. The most widely used materials for ferroelectric applications are mainly pure inorganic oxides such as BaTiO3, LiNbO3, and PbZr1–xTixO3, due to their superior electric properties, high thermal stability and phase transition temperature. Recent studies have shown that ferroelectric metal-organic molecule based materials are a promising candidates to replace the predominant lead-based ferroelectrics. [1, 2] The strategy in design of molecular ferroelectrics frequently relies on rotating polar globular ionic molecules, such as 1- azabicyclo[2.2.2]octane (ABCO), as they can be readily reoriented in response to an applied electric field and induce ferroelectric polarization. In attempt to prepare new molecular ferroelectric systems different bicyclic amine cations, including simple derivatives of globular ABCO molecule (O-ABCO = 1-azabicyclo[2.2.2]octan- 3-one ; COOH-OH-ABCO = 3-hydroxy-1- azabicyclo[2.2.2]octane-3-carboxylic acid) and more complex chiral natural alkaloids with ABCO fragment (Q= quinine ; Cnd = cinchonidine) have been used in reactions with chlorocobaltate(II) anions. A series of complexes of the formula ACoCl3 (A = O-ABCO, COOH-OH-ABCO, Q, Cnd) has been prepared. By using the combined techniques of variable-temperature powder X-ray structural analyses, differential scanning calorimetry, impedance spectroscopy, and polarization-voltage measurements, we revealed exciting structural and electric properties in this series of compounds.