Structure and optical properties of several organic-inorganic hybrids containing corner-sharing chains of bismuth iodide octahedra

Abstract

Two organic -inorganic bismuth iodides of the form (H3N-R-NH3)BiI5 are reported, each containing long and relatively flexible organic groups, R. The inorganic framework in each case consists of distorted BiI6 octahedra sharing cis vertexes to form zigzag chains. Crystals of (H3NC18H24S2NH3) BiI5 were grown from a slowly cooled ethylene glycol/2-butanol solution containing bismuth(III) iodide and AETH·2HI, where AETH = 1,6-bis[5′-(2″-aminoethyl)-2′-thienyl]hexane. The new compound, (H2AETH)BiI5, adopts an orthorhombic (Aba2) cell with the lattice parameters a = 20.427(3) Å, b = 35.078(5) Å, c = 8.559(1) Å, and Z = 8. The structure consists of corrugated layers of BiI52- chains, with Bi-I bond lengths ranging from 2.942(3) to 3.233(3) Å, separated by layers of the organic (H2AETH)2- cations. Crystals of the analogous (H3NC12H24NH3)BiI5 compound were also prepared from a concentrated aqueous hydriodic acid solution containing bismuth(III) iodide and the 1,12-dodecanediamine (DDDA) salt, DDDA·2HI. (H2DDDA)BiI5 crystallizes in an orthorhombic (Ibam) cell with a = 17.226(2) Å, b = 34.277(4) Å, c = 8.654(1) Å, and Z = 8. The Bi-I bonds range in length from 2.929(1) to 3.271(1) Å. While the inorganic chain structure is nearly identical for the two title compounds, as well as for the previously reported (H3NC6H12NH3)BiI5 [i.e., (H2DAH)BiI5] structure, the packing of the chains is strongly influenced by the choice of organic cation. Optical absorption spectra for thermally ablated thin films of the three organic-inorganic hybrids containing BiI52- chains are reported as a function of temperature (25-290 K). The dominant long-wavelength feature in each case is attributed to an exciton band, which is apparent at room temperature and, despite the similar inorganic chain structure, varies in position from 491 to 541 nm (at 25 K).