p-Block Catecholates: A Century-Old Platform for Hybrid Molecular Ferroelectrics.

Abstract

p-Block catecholato complexes are known for their robustness, structural diversity, and high synthetic modularity, yet their potential as functional electronic materials has remained unexplored. In this study, we investigate p-block catecholato complexes as molecular ferroelectrics for the first time. A series of germanium catecholato salts, [Bu4N][Cl-Ge(cat)2], [Pr4N][Cl-Ge(cat)2], and [Et4N][Cl-Ge(cat)2], was synthesized to assess the influence of counter-cation size on crystal symmetry and polar order. Single-crystal x-ray diffraction reveals a counter-cation-dependent transition from centrosymmetric to polar packing, while second-harmonic generation confirms the noncentrosymmetric nature of [Et4N][Cl-Ge(cat)2] at 290 K. Dielectric spectroscopy, capacitance-voltage measurements, and double-wave electrical measurements support switchable polarization in thin films. Piezoresponse force microscopy reveals characteristic amplitude butterfly loops and phase hysteresis, further corroborating reversible piezoelectric switching. These findings establish p-block catecholato complexes as a chemically programmable platform for counter-cation-controlled hybrid molecular ferroelectrics.

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