2, University of Cambridge, Cambridge, Cambridgeshire, United Kingdom
3, Indian Institute of Technology Bombay, Mumbai, , India
The recent use of hybrid ABX3 perovskites where A is a molecular species and X is a monatomic halide has led to a revolution in advanced solar cells and has sparked significant interest in the synthesis and characterisation of various species of perovskite with unique electrical properties. In addition, the development of perovskites where both A and X are molecular is a source of great interest in the field of advanced materials, particularly the well-known functional properties of the X = formate perovskites including multiferroicity, and their complex responses to pressure and temperature changes. The total number of perovskite families with distinct molecular X-sites is low, so the synthesis of perovskites with novel molecular X anions is of special interest. We present a new family of hybrid perovskites synthesised with X = hypophosphite ([H2POO-]), a phosphorus analogue of the formate ligand that is cheap, easily accessible, and non-toxic. We demonstrate the rich crystal chemistry of this family, having the composition [Am](Mn)(H2POO)3, with Am = guanidinium, formamidinium, imidazolium, triazolium, and DABCOnium. Their wide range of thermal phase transitions were thoroughly characterised by single-crystal X-ray diffraction, and we show the contrasting antiferromagnetism of the guanidinium phase and the paramagnetism of the formamidinium phase arising from pronounced perovskite layer shearing, behaviour not seen in other molecular perovskite families.