Structure-bandgap tunability of metal halide perovskites: Synthesis, spectral, single crystal X-ray structural, BVS, CShM and Hirshfeld surface analysis of piperidinium hexahalostannates(IV)

Abstract

Metal halide perovskites such as piperidinium hexachlorostannate(IV) and piperidinium hexabromostannate(IV) were prepared along with their ammonium analogues ((1) and (2)) and were analyzed by IR, 1H, 13C NMR, DRS techniques. Single crystal X-ray structures were determined and Bond valence sums (BVS), Continuous Shape Measure (CShM) parameters were deduced from structural data. Broad IR bands were observed for υNH2 vibrations (3388, 3383 cm–1) long with characteristic δNH bending vibrations (1571, 1573 cm–1). TG–DT analysis confirmed the proposed formulae of (1) to (4). Band gaps of the hybrids derived from the DRS study followed the decreasing order: (NH4)2SnCl6 >(C5H10NH2)2SnCl6 >(NH4)2SnBr6 > (C5H10NH2)2SnBr6. Ammonium hybrids (1) & (2) and the piperidinium analogues (3) & (4) are isostructural. Differentiation of Sn-Xaxial/equatorial bonds and distortion of X–Sn–X bond angles observed in (3) and (4) are due to the substitution of ammonium cation by bulky piperidinium cation. The crystal structures are stabilized by intermolecular N–H···X interactions. BVS for (1), (2), (3) and (4) are: 4.12, 4.01, 3.96 and 3.92 respectively, which established the formal oxidation state of tin as quadripositive. CShM for (1), (2), (3) and (4) are: 0.0000, 0.0000, 0.0172 and 0.0103 respectively, indicating octahedral environment of halogen atoms around tin. Shape Index map of (C5H10NH2)2SnBr6 (4) with the least band gap tends to be spherical compared to other compounds.