α- to β-[C6H4(NH3)2]2Bi2I10 reversible solid-state transition, thermochromic and optical studies in the p-phenylenediamine-based iodobismuthate(III) material

alpha-[C6H4(NH3)(2)](2)Bi2I10, which is a new material containing low-dimensional iodobismuthate anions, was synthesized and through its single crystal X-ray diffraction measurements, was proven to crystallize at room temperature in the centrosymmetric space group P2(1)/c. It consists of a p-phenylenediammonium dication and a discrete (0-D) anion built up of edge-sharing bioctahedron. Due to the hydrogen bonds and the interatomic distances (Bi-I, I center dot center dot center dot I and pi-pi) changes, alpha-phase was transformed into the corresponding centrosymmetric beta-phase, beta-[C6H4(NH3)(2)](2)Bi2I10, through a single-crystal to single-crystal transformation occurring upon cooling to -28/-26 degrees C. Below the transition temperature, beta-[C6H4(NH3)(2)](2)Bi2I10 crystallizes in the monoclinic system, centrosymmetric space group P2(1)/n. Besides, the optical transmission measurements on alpha-[C6H4(NH3)(2)](2)Bi2I10 thin films have revealed two absorption bands at 2.47 and 3.01 eV. Finally, two room temperature photoluminescence emissions attributed to excitons radiative recombinations confined within the bioctahedra Bi2I104-, were observed in the red spectral range at 1.9 and 2.05 eV energy. (C) 2011 Elsevier Inc. All rights reserved.