Metal – organic hybrids of tin(IV) with tuneable band gap: Synthesis, spectral, single crystal X-ray structural, BVS and CSM analysis of morpholinium hexahalostannate(IV)

Abstract

Self assembled organic - inorganic hybrid materials such as morpholinium hexachlorostannate(IV) (3) and morpholinium hexabromostannate(IV) (4) have been synthesised from morpholinium chloride (1) and morpholinium bromide (2) at room temperature. The hybrids were characterized by elemental analysis, IR, NMR, TG-DTA, DRS and PL spectroscopy and single crystal X-ray diffraction. IR and NMR spectral data of (3) and (4) show very little changes compared to their parent compounds (1) and (2). However, the = NH2+ proton signal of the bromide hybrid (4), shows a relatively lower δ value due to extensive hydrogen bonding compared to its chloride analogue (3). Thermal analysis confirmed the proposed formulae of the compounds. Optical absorption measurements showed 3.80 and 2.60 eV as band gaps for (3) and (4) respectively at room temperature implying that the band gaps can be easily tuned by altering the halide ion. Single crystal X-ray structures of compounds (3) and (4) revealed extensive hydrogen bonded interactions between the morpholinium cation and the SnCl62− and SnBr62− anions in (3) and (4). In (4), two molecules of morpholinium bromide co-crystallized with the hybrid. BVS calculations performed on SnCl62− and SnBr62− anions (3) and (4) resulted in 4.10 and 4.13 respectively, which clearly established the formal oxidation state of tin in the compounds as 4+. CSM calculation on SnBr62− yielded a value of 0.006 signifying a near perfect octahedral geometry of the anion.