New geometric degrees of freedom in ReO3-type coordination networks Sebastian Hallweger 1 , Dr. Gregor Kieslich 2 1. Technical University of Munich, TUM School of Natural Sciences,Department of Chemistry, Lichtenbergstraße 4, 85748 Garching, Germany 2. Technical University of Munich, TUM School of Natural Sciences, Department of Chemistry, Lichtenbergstraße 4, 85748 Garching, Germany Molecular perovskites, i.e. coordination networks with a ABX 3 perovskite structure where the A- and/or X‑site are replaced by molecular building units, have attracted great attention over the last decade. The use of organic as well as organometallic ions in molecular perovskites motivates for systematically studying and tuning their chemical and physicochemical properties such as barocaloric [1] , ferroelectric [2] , and multiferroic behaviour [3] as well as their complexities [4] and optoelectronic properties [5] . In my poster, I will introduce and discuss structure-property relationships in a recently discovered material class of molecular perovskites with new geometric degrees of freedom (gDOFs). [6] By using divalent A-site cations such as [R 3 N(CH 2 ) n NR 3 ] 2+ ( n = 4,5), the spatial arrangement of A 2+ cations within the ReO 3 -type BX 3 ([B(C 2 N 3 ) 3 ] - ; with B = Mn 2+ , Ni 2+ and Co 2+ ) is introduced as a new gDOF. For materials such as (TPC4TP)[Mn 2 (C 2 N 3 ) 6 ] (with TPC4TP = (C 3 H 7 ) 3 N(CH 2 ) 4 N(C 3 H 7 ) 3 2+ ) and (TPC5TP)[Mn 2 (C 2 N 3 ) 6 ] (TPC5TP = (C 3 H 7 ) 3 N(CH 2 ) 5 N(C 3 H 7 ) 3 2+ ), a herringbone and head-to-tail order pattern are observed, with ramifications on their thermal and pressure responsive properties. For instance, variable pressure and temperature diffraction show uniaxial negative thermal expansion for both compounds and negative linear compression for (TPC4TP)[Mn 2 (C 2 N 3 ) 6 ], which is related to the herringbone structure-motif. Based on this work, I will discuss on how sterical effects, i.e. by chemical modification of R-substituents on the ammonium groups, influence the materials’ responsive properties to temperature and pressure. References 1. J. M. Bermúdez-García, M. Sánchez-Andújar, S. Castro-García, J. López-Beceiro, R. Artiaga, M. A. Señarís-Rodríguez, Nat Commun 2017 , 8 , 15715. 2. H.-Y. Ye, Y.-Y. Tang, P.-F. Li, W.-Q. Liao, J.-X. Gao, X.-N. Hua, H. Cai, P.-P. Shi, Y.-M. You, R.-G. Xiong, Science 2018 , 361 , 151. 3. P. Jain, V. Ramachandran, R. J. Clark, H. D. Zhou, B. H. Toby, N. S. Dalal, H. W. Kroto, A. K. Cheetham, J Am Chem Soc 2009 , 131 , 13625. 4. S. A. Hallweger, C. Kaußler, G. Kieslich, Phys Chem Chem Phys 2022 , 24 , 9196. 5. D. Stefańska, Molecules 2022 , 27 . 6. S. Burger, K. Hemmer, D. C. Mayer, P. Vervoorts, D. Daisenberger, J. K. Zaręba, G. Kieslich, Adv Funct Materials 2022 , 32 , 2205343.
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