Single crystals of formamidinium (FA)–lead–chloride–dimethyl sulfoxide (DMSO) solvate, [CH(NH2)2]Pb(C2H6OS)Cl3, were synthesized from a DMSO ((CH3)2SO) solution in which FA–chloride (CH(NH2)2Cl) and lead(II) chloride (PbCl2) were dissolved. Single-crystal X-ray diffraction studies revealed that [CH(NH2)2]Pb(C2H6OS)Cl3 exhibited a monoclinic (P21/c) symmetry in the temperature range of 113–293 K. Interestingly, the oxygen atom of DMSO was involved in the distorted [PbOCl5] octahedra, which form a [Pb2O2Cl9] dimer unit by edge-sharing. These dimer units form a pseudo-2D zigzag layer elongated parallel to the (100) plane via corner sharing. The FA+ cation was structurally ordered and aligned between the pseudo-2D zigzag layers at the voids surrounded by the [Pb2O2Cl9] dimer units. The formation enthalpy of the DMSO solvate calculated using the density functional theory method explains the phase stability of the FAPbCl3–DMSO solvate.
