Designing Geometric Degrees of Freedom in ReO₃‐Type Coordination Polymers

Abstract

Engineering the interplay of structural degrees of freedom that couple to external stimuli such as temperature and pressure is a powerful approach for material design. New structural degrees of freedom expand the potential of the concept, and coordination polymers as a chemically versatile material platform offer fascinating possibilities to address this challenge. Here, we report a new class of perovskite-like AB 2 X 6 coordination polymers based on a [BX 3 ] − ReO 3 -type host network ([Mn(C 2 N 3 ) 3 ] − ), in which the spatial orientation of divalent A 2+ cations ([R 3 N(CH 2 ) n NR 3 ] 2+ ) with separated charge centers that bridge adjacent ReO 3 -cavities is introduced as a new geometric degree of freedom. Herringbone and head-to-tail order pattern of [R 3 N(CH 2 ) n NR 3 ] 2+ cations are obtained by varying the separator length n and, together with distortions of the pseudocubic [BX 3 ] − network, they determine the materials' stimuli-responsive behavior such as counterintuitive large negative compressibility and uniaxial negative thermal expansion. This new family of coordination polymers highlights the chemists' capabilities of designing matter on a molecular level to address macroscopic material functionality and underpins the opportunities of the design of structural degrees of freedom as a conceptual framework for rational material synthesis in the future.

Narrowing the tolerance factor limits for hybrid organic-inorganic dicyanamide-perovskites

“…For example, most recently Burger et al [49] have reported new and very interesting perovskite-like AB 2 X 6 compounds based on a [BX 3 ] À ReO 3 -type host network ([Mn(C 2 N 3 ) 3 ] À ), in which the divalent A 2þ cations ([Pr 3 N(CH 2 ) n NPr 3 ] 2þ with n ¼ 4 and 5) with separated charge centers bridge adjacent A-site cavities. To test the validity of the here proposed procedure beyond "conventional" perovskites, we have estimated the volume of these two divalent organic A-cations using the CrystalExplorer software.…”

Tuning the mechanical properties of dicyanamide-based molecular perovskites

“…Conceptually, the use of molecular A-and X-site species enhances the structural and chemical diversity in these perovskites, leading to new opportunities for tuning macroscopic material behaviour. 6 Examples are tilt-and-shift engineering to impart ferroelectric properties, 7,8 tunability of hydrogen bonding interactions 9 between the A-site cation and the 3D [BX 3 ] − network with ramifications on the mechanical response, 10,11 adjustable phase transition thermodynamics, 12,13 and varying structural complexities 14 amongst others.…”

Tuning the Mechanical Properties of Dicyanamide-Based Molecular Perovskites

“…Conceptually, the use of molecular A-and X-site species enhances the structural and chemical diversity in these perovskites, leading to new opportunities for tuning macroscopic material behaviour. 6 Examples are tilt-and-shift engineering to impart ferroelectric properties, 7,8 tunability of hydrogen bonding interactions 9 between the A-site cation and the 3D [BX3]network with ramifications on the mechanical response, 10,11 adjustable phase transition thermodynamics, 12,13 and varying structural complexities 14 amongst others.…”