SYNTHESIS, CRYSTAL-STRUCTURE, AND OPTICAL AND THERMAL-PROPERTIES OF (C4H9NH3)(2)MI(4) (M=GE, SN, PB)

Single crystals of the organic-inorganic layered perovskites (C4H9NH3) (2)MI(4) (M = Ge, Sn, Pb) have been grown from aqueous hydriodic acid solutions. X-ray diffraction, thermal analysis, and photoluminescence spectroscopy were used to compare crystal structure, metal atom lone-p air stereoactivity, and physical properties as a function of group IVB element. The orthorhombic (C4H9NH3)(2)GeI4 structure, refined in the space group Pcmn, consists of single-layer-thick perovskite sheets of distorted corner-sharing GeI6 octahedra separated by n-butylammonium c ation bilayers. (C4H9NH3)(2)SnI4 and (C4H9NH3)(2)PbI4 are structurally very similar but adopt the space group Pbca, with a more ideal octahe dral iodine coordination around the divalent group IVB atoms. Within t he more general tin(II)-based family, (C4H9NH3)(2)(CH3NH3)(n-1)SnnI3n1, a structural comparison between the title semiconducting n = 1 comp ound and the previously reported semimetallic n = 3 and metallic n --> infinity members demonstrates a correlation between perovskite sheet thickness, Sn(II) lone-pair stereochemical activity, average Sn-I bond length, and electrical conductivity within this series. While (C4H9NH 3)(2)GeI4 melts at 222(2) degrees C, significantly below its bulk deco mposition temperature, (C4H9NH3)(2)SnI4 (T-m = 256(2) degrees C) and ( C4H9NH3)(2)PbI4 (T-m = 285(4) degrees C) melt/decompose at progressive ly higher temperatures and are less stable as a melt. Room-temperature photoluminescence from the title compounds exhibits a pronounced spec tral peak in the visible range, with the peak wavelength varying betwe en 690(5), 625(1), and 525(1) nm for the M = Ge, Sn, and Pb compounds, respectively.