Evidence and detailed study of a second-order phase transition in the (C6H11NH3)2[PbI4] organic-inorganic hybrid material (original) (raw)
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Phys. Chem. Chem. Phys., 2002
Layered organic-inorganic hybrids based on perovskite-derived alkylammonium lead halides have been demonstrated as important new materials in the construction of molecular electronic devices. Typical of this class of materials are the single-perovskite slab lead iodides of the general formula (C n H 2n+1 NH 3) 2 PbI 4. While for small n, these compounds are amenable to single-crystal structure determination, the increasing degree of disorder in the long chain (n ¼ 12,14.. .) compounds makes such an analysis difficult. In this study, we use powder X-ray diffraction, and vibrational and 13 C NMR spectroscopies to establish the conformation, orientation and organization of hydrocarbon chains in the series of layered alkylammonium lead iodides (C n H 2n+1 NH 3) 2 PbI 4 (n ¼ 12,16,18). We find that the alkyl chains adopt a tilted bilayer arrangement, while the structure of the inorganic layer remains invariant with respect to the value of n. Conformation-sensitive methylene stretching modes in the infrared and Raman spectra, as well as the 13 C NMR spectra indicate that bonds in the methylene chain are in trans configuration. The skeletal modes of the alkyl chain in the Raman spectra establish that there is a high degree of all-trans conformational registry for the values of n studied here. From the orientation dependence of the infrared spectra of crystals of (C n H 2n+1 NH 3) 2 PbI 4 (n ¼ 12,16), we find that the molecular axis of the all-trans alkyl chains are tilted away from the interlayer normal by an angle of 55. This value of this tilt angle is consistent with the dependence of the c lattice expansion as a function of n, as determined from powder X-ray diffraction.
Three inorganic–organic layered perovskite-type hybrids of the general formula [(CnH2n + 1NH3)2PbI4], n = 4, 5 and 6, display a number of reversible first-order phase transitions in the temperature range from 256 to 393 K. [(C4H9NH3)2PbI4] has a single phase transition, [(C5H11NH3)2PbI4] has two phase transitions and [(C6H13NH3)2PbI4] has three phase transitions. In all three cases, the lowest-temperature phase transition is thermochromic and the crystals change colour from yellow in their lowest-temperature phase to orange in their higher-temperature phase for [(C4H9NH3)2PbI4] and [(C6H13NH3)2PbI4], and from orange to red for [(C5H11NH3)2PbI4]. The structural details associated with this phase transition have been investigated via single-crystal X-Ray diffraction, SC-XRD, for all three compounds.
CrystEngComm, 2016
BisIJdiisobutylammonium) octabromodiantimonateIJIII), [(i-C 4 H 9) 2 NH 2 ] 2 Sb 2 Br 8 , has been synthesized. The differential scanning calorimetric measurements indicate a reversible, first-order phase transition at 222/ 229 K (cooling/heating). The single crystal X-ray diffraction studies reveal that the phase transition is isomorphous and is accompanied by a huge distortion of the crystal lattice. By comparison of the crystal structures of [(i-C 4 H 9) 2 NH 2 ] 2 Sb 2 Br 8 and [(i-C 4 H 9) 2 NH 2 ] 2 Sb 2 Cl 8 , an analogous mechanism of the phase transition of the former is proposed. The change of the electronic structure of the complex during the phase transition was analyzed by UV-vis spectroscopy. A low-frequency dielectric relaxation process appears over phase I (below the room temperature) and corresponds to the dynamics of dipolar diisobutylammonium cations. The detailed analysis of the molecular motions of the organic cations studied by means of proton magnetic resonance (1 H NMR) in a wide temperature range indicates a leading role of the methyl groups in the relaxation mechanism. A variable-temperature investigation of the infrared spectra of [(i-C 4 H 9) 2 NH 2 ] 2 Sb 2 Br 8 confirms, in turn, the influence of the diisobutylammonium cation dynamics on the molecular mechanism of the structural transformation at 229 K.
The dynamics of the thermally induced first-order structural phase transition in a high-quality single crystal of the organic-inorganic perovskite (C12H25NH3)2PbI4 was investigated by optical microscopy. The propagation of the straight phase front (habit plane) during the phase transition along the cooling and heating pathways of the thermal hysteresis was observed. The thermochromic character of the transition allowed monitoring of the thermal dependence of average optical density and aided the visualization of the interface propagation. The thermal hysteresis loop is 10 K wide, and the interface velocity is constant at V ≈ 1.6 mm s–1. The transition is accompanied with sizeable change in crystal size, with elongation of ~6% along the b axis and compression of ~ –2% along the a axis, in excellent agreement with previously reported X-ray diffraction data. The progression of the habit plane is at least 160 times faster than in spin-crossover materials, and opens new prospects for organic-inorganic perovskites as solid switching materials. Moreover, the crystals of (C12H25NH3)2PbI4 are unusually mechanically robust and present excellent resilience to thermal cycling. These hitherto unrecognized properties turn this and possibly similar hybrid perovskites into perspective candidates as active medium for microscopic actuation.
Crystal structure of the high-temperature polymorph of C(NH2)3PbI3 and its thermal decomposition
Journal of Alloys and Compounds
The synthesis of guanidinium lead iodide, C(NH 2) 3 PbI 3 (GUAPbI 3), was conducted by slow evaporation of the mixture obtained by dissolving PbI 2 and C(NH 2) 3 I in acetonitrile. When the evaporation is done at 40 ºC, a yellow needle-like crystals are being formed. The sample was characterized by elemental analysis, density measurements, scanning electron microscopy, thermal analyses, high-temperature X-ray powder diffraction and infrared spectroscopy measurements. The elemental analysis of the obtained crystals confirmed the proposed stoichiometry. The performed thermal analyses showed an endothermic peak associated with structural transition around 160 ºC. On the other hand, the endothermic temperature effects above 300 ºC are accompanied with mass loss and were interpreted as compound degradation. The crystal structure of high temperature polymorph between 160 ºC and 300 ºC was determined using high-temperature powder diffraction data measurements at 280 ºC using simulated annealing technique in order to obtain initial structural model. The structure was refined using the Rietveld method. At temperatures higher than 160 ºC, C(NH 2) 3 PbI 3 crystallizes in hexagonal space group P6 3 mc with unit cell parameter a increasing from 9.269 Å to 9.337 Å between 160 ºC and 300 ºC and c parameter increasing from 15.211 Å to 15.287 Å in the same temperature range. The structure consists of PbI 6 octahedra couples sharing a common face, linked with corners. Guanidinium cations are situated in the channels between Pb 2 I 9 couples in a manner that the plane of the molecule is perpendicular to the c-axis.
Journal of Molecular Structure, 2010
The tri (dimetylammonium) hexa-iodobismuthate of general formula [(CH3)2NH2]3[BiI6] is an organic–inorganic hybrid material. The crystal lattice is composed of discrete [BiI6] anions surrounded by dimethylamine cations. The X-ray diffraction pattern was obtained and indexed on the basis of rhombohedra unit cell with the R3¯ space group. Room temperature IR and Raman spectra of the title compound were recorded and analyzed. Semi-empirical Parameter Model three (PM3) method as well as density functional theory (DFT) calculations have been performed to derive the equilibrium geometry, vibrational wave numbers and a prediction of IR and Raman spectral activities. In this compound the bands corresponding to the cation vibrational modes show that the symmetry of these cations is distorted and they are strongly hydrogen bonded to the respective anions. The frontier molecular orbital and the energy gap between the highest occupied molecular orbital (HOMO) and the lowest un-occupied molecular orbital (LUMO) were calculated with time dependent density functional theory (TD-DFT). The results show good consistent with the experiment and confirm the contribution of metal orbital to the HOMO–LUMO boundary.
Journal of Materials, 2014
The organic-inorganic hybrid compound (C13H28N2) BiCl5was synthesized by solvothermal method. The crystal structure was solved by single-crystal X-ray diffraction. The compound crystallizes in the orthorhombic system space group Cmc21witha=15.826(4) Å,b=18.746(6) Å,c=7.470(3) Å, andZ=4. The crystal structure was refined down toR=0.019. It consists of corrugated layers of [BiCl5]2−chains, separated by organic [H2TMDP]2+cations (TMDP=1,3-Bis(4-piperidyl)propane = C13H26N2). The crystal cohesion is achieved by hydrogen bondsN–H⋯Cljoining the organic and inorganic layers. The influence of the organic cations' flexibility is discussed. Raman and infrared spectra of the title compound were recorded in the range of 50–400 and 400–4000 cm−1, respectively. Semiempirical parameter model three (PM3) method has been performed to derive the calculated IR spectrum. The crystal shape morphology was simulated using the Bravais-Friedel and Donnay-Harker model.