Structural analysis of alkyl chain conformation in the layered organic–inorganic hybrids (CnH2n+1NH3)2PbI4 (n=12,16,18) by IR spectroscopy

The conformational order and planarity of alkyl chains in the organic–inorganic hybrid materials (CnH2n+1NH3)2PbI4, have been examined using infrared spectroscopy. The structure of the inorganic PbI4 slabs in these compounds are invariant with respect to the value of n. These inorganic slabs are sandwiched by bilayers of long alkylammonium chains. The coupling of vibrational modes of all-trans segments of the alkyl chains produce band progressions that are diagnostic of the all-trans conformation. From an analysis of the rocking, twisting, and wagging vibrational mode progressions we establish that irrespective of the value of n all methylene units of the alkyl chain in (CnH2n+1NH3)2PbI4 are in trans registry at room temperature.