In the first step, we designed a range of A + to produce a series of molecular perovskites that can be used to determine how structural and pressure responsive properties are altered by small chemical changes. In this pursuit, we synthesised a series of piperidinium derivatives ([DIP] + , [PEP] + , [DEP] + and [DPP] + ), where different alkyl chain modifications of the piperidinium nitrogen enable studying the impact of small variations in size and/or shape (Fig. ). All A + were synthesised via nucleophilic substitution of halides, see SI for details (Fig. -S5 and S11-S18). For instance, [DEP] + was obtained from the reaction of diethylamine and 1,5-dibromopentane in acetonitrile. Single crystals of the [A]Ni(C2N3)3 series were obtained by a mildsolution crystallisation route that has previously been used for the synthesis of related materials, see SI for details (S-5). In a typical reaction, the precursor materials [A]Br, Na(C2N3) and Ni(NO3)26H2O are dissolved in water, mixed and then left to crystallise overnight in a refrigerator. An overview of all synthesised compounds in this work is given in Table .