A new organic inorganic hybrid material (C15H14N4)BiBr5 center dot H2O with an optical band gap of 2.24 eV, having 1-D chains of bromobismuthate anions in its composition, has been obtained from an aqueous solution and characterized. The partial replacement of Br by I resulted in the formation of a thermally stable (<155 degrees C) black compound (C15H14N4)BiBrI4 center dot H2O with an optical band gap of 1.70 eV, which can be proposed as a promising light-harvesting material for dye-sensitized solid-state solar cells. Further replacement of Br by I results in the formation of red-orange colored (C15H14N4)BiI5 with a band gap of 2.10 eV.
Three hybrid 1,1'-(1,n-alkanediyl)bis(4-methylpyridinium) iodobismuthates 1 - 3 were prepared by a facile solution route and showed thermal stability in air up to 230°C. The structures of solid 1 and 3 contain zero-dimensional anions, and the structure of 2 contains one-dimensional linear anionic chains [BiI5]n2n-. Photoluminescence (PL) in the spectral range between 600 and 750 nm was observed for 1 and 2. DFT calculations and optical studies confirmed that compounds 1−3 are semiconductors with band gaps of 1.73−2.10 eV, which corresponds with their intense black (for 2) or red (for 1 and 3) colors. The optical absorption of 2 in the red spectral range is primarily due to charge transfer from the I5p orbitals at the top of the valence band to the Bi6p orbitals at the bottom of the conduction band.
Conditions for a sulfate method for the synthesis of a metastable modification, which has been previously described as ‘‘Z-TiO2’’ (Dadachov, 2006), were found and the stability region of this phase in the hydrolysis temperature–hydrolysis duration coordinates was determined. Investigation by a number of methods (X-ray powder diffraction, a differential dissolution method, thermogravimetry, IR spectroscopy, Raman spectroscopy) showed that the Z-phase is not a polymorph of TiO2 but is a pseudo-polymorph of titanium dioxide hydrate. It was demonstrated that nanoparticles of the lowtemperature Z-phase consist of the [TiO2xmH2O] core, the structure of which can be described as a superstructure in relation to anatase, and an amorphous shell containing TiO2x (trace amount), OH, HSO4 and water. The average crystallite size depends on the ratio of the constituents.