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Conformation and orientation of alkyl chains in the layered organic-inorganic hybrids: (CnH2n+1NH3)(2)PbI4 (n=12,16,18)

Venkataraman, NV and Bhagyalakshmi, S and Vasudevan, S and Seshadri, Ram (2002) Conformation and orientation of alkyl chains in the layered organic-inorganic hybrids: (CnH2n+1NH3)(2)PbI4 (n=12,16,18). In: PCCP: Physical Chemistry Chemical Physics, 4 (18). pp. 4533-4538.

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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 (CnH2n+1NH3)(2)PbI4. While for small n, these compounds are amenable to single-crystal structure determination, the increasing degree of disorder in the long chain (n = 12,14...) compounds makes such an analysis difficult. In this study, we use powder X-ray diffraction, and vibrational and C-13 NMR spectroscopies to establish the conformation, orientation and organization of hydrocarbon chains in the series of layered alkylammonium lead iodides (CnH2n+1NH3)(2)PbI4 (n = 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 C-13 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 (CnH2n+1NH3)(2)PbI4 ( n = 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 55degrees. 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.

Item Type: Journal Article
Publication: PCCP: Physical Chemistry Chemical Physics
Publisher: Royal Society of Chemistry
Additional Information: Copyright of this article belongs to Royal Society of Chemistry.
Department/Centre: Division of Chemical Sciences > Inorganic & Physical Chemistry
Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited: 22 Jul 2011 07:31
Last Modified: 22 Jul 2011 07:31
URI: http://eprints.iisc.ac.in/id/eprint/39064

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