First representatives of (210)-oriented perovskite variants−Synthesis, crystal structures and properties of the new 2D hybrid perovskites A[HC(NH2)2]PbI4; A=[C(NH2)3], [HSC(NH2)2]

Single crystals of [C(NH2)3][HC(NH2)2]PbI4 (GuFAPbI4) and [HSC(NH2)2][HC(NH2)2]PbI4 (TuFAPbI4) were obtained from solutions of the binary halides in HI or DMF. Large crystals grown from HI are dark-brown while single phase powders synthesized from DMF are orange. The crystal structure of GuFAPbI4 (I2/m, Z=12, a=14.3147(2), b=12.7591(2), c=25.7377(4)Å), β=101.459(1), 4256 refl., 196 param., R1=0.024, wR2=0.061) represents a 2D perovskite with a new motif similar to Ruddlesden-Popper phases (AX)m(A′BX3)n and m=n=1. The layers are formed by corner-sharing PbI6 octahedra. According to the cut-out of the 3-D perovskite the structure of GuFAPbI4 can be assigned as a (210)-oriented representative. So one octahedron is linked in trans-position and two in cis-orientation. The structure of TuFAPbI4 (P21/n, Z=12, a=14.4208(6), b=12.7545(7), c=26.3982(11) Å), β=100.609(3)°, 6808 refl., 275 param., R1=0.048, wR2=0.096) represents a simple distortion variant of GuFAPbI4. GuFAPbI4 and TuFAPbI4 were further characterized by vibrational spectroscopy and optical spectroscopy. The optical band gap was determined as 2.34 eV in agreement to the observed color. So both compounds are not suitable as a dye in the PSC perovskite solar cell. Similar to other Pb-containing 2D perovskites there is a significant excitonic peak (2.31 eV). TuFAPbI4 represents the first example with protonated thiourea as an organic cation. Therefore, we characterized protonated thiourea iodide and introduce protonated thiourea [HSC(NH2)2]+ as a new cation for hybrid halogeno perovskites. [ABSTRACT FROM AUTHOR]