A Series of New Phases Containing Three Different Asymmetric Building Units

Systematic explorations of the new phases in the Pb^II/Bi^III−TM(d⁰/d¹)−Se^IV−O systems by hydrothermal syntheses led to five new quaternary phases whose structures are composed of three different asymmetric building units, namely, Pb₂V^V₂Se₂O₁₁ (1), Pb₂V^IV₃Se₅O₁₈ (2), Pb₂Nb^V₂Se₄O₁₅ (3), Bi₂V^V₂Se₄O₁₆ (4), and Bi₂Mo^VI₂Se₂O₁₃ (5). The structure of 1 features a 3D network built by 1D anionic chains of [V₂O₅(SeO₃)₂]⁴⁻ interconnected by Pb²⁺ ions with six-membered-ring (MR) tunnels along the b axis. The structure of 2 features a 3D anionic framework composed of V^IVO₆ octahedra corner-sharing with SeO₃ anions, with the Pb²⁺ ions located at the resultant 8-MR tunnels. The oxidation state of the vanadium cation is 4+ due to the partial oxidation of V₂O₃ by SeO₂ at high temperature. The structure of 3 features novel 1D double chains of [Nb₂O₃(SeO₃)₄]⁴⁻ that are interconnected by Pb²⁺ ions, forming a 3D network with 12-MR tunnels along the c axis. 4 features a 3D framework composed of 2D layers of [Bi₂(SeO₃)₂]²⁺ and 1D [(VO₂)₂(SeO₃)₂]²⁻ double chains. The structure of 5 features a 3D network composed of bismuth(III) selenite with large 10-MR tunnels along the a axis that are occupied by Mo₂O₁₀ dimers. The results of optical diffuse-reflectance spectrum measurements and electronic structure calculations based on density functional theory methods indicate that all five compounds are wide-band-gap semiconductors. Luminescent property measurements for compounds 1−5 and magnetic measurements for compound 2 were also made.