A series of new silver selenites with d0-TM cations

Abstract

Systematic explorations of new phases in the Ag⁺–Ti⁴⁺/Zr⁴⁺/Nb⁵⁺/Ta⁵⁺–Se⁴⁺–O(F) system by hydrothermal syntheses or standard high temperature solid-state reactions resulted in four new mixed-metal silver selenites, namely, Ag₃Ti₃O₃(SeO₃)₄F (1, P6₃), Ag₂ZrF₂(SeO₃)₂ (2, Cmca) and AgMO(SeO₃)₂ (M = Nb, 3; Ta, 4) in the space group Cmcm. Ag₃Ti₃O₃(SeO₃)₄F features an interesting [Ti₃O₃(SeO₃)₄]²⁻ 3D anionic framework composed of 1D chains of corner-sharing TiO₆ octahedra which are further interconnected by tridentate bridging SeO₃²⁻ anions, displaying 1D hexagonal channels of Ti₆Se₆ 12-member rings (MRs) along the c-axis, filled by the Ag⁺ cations and isolated F⁻ anions. More interestingly, it displays a moderate strong Second-Harmonic Generation (SHG) response about 2 times that of KH₂PO₄ (KDP). Compound 2 features a novel 1D [ZrF₂(SeO₃)₂]²⁻ anionic chain composed of edge-sharing ZrO₄F₄ polyhedra in which two neighboring Zr⁴⁺ cations are further bridged by a pair of selenite anions. Compounds 3 and 4 are isostructural and their structures feature 1D anionic chains of [MO(SeO₃)₂]⁻ (M = Nb, Ta) which are separated by Ag⁺ cations, the 1D [MO(SeO₃)₂]⁻ (M = Nb, Ta) chain is formed by 1D chains of corner-sharing MO₆ (M = Nb, Ta) octahedra in which two neighboring metal centers are also bridged by a pair of selenite anions. Other characterizations including thermal analyses, optical and luminescence property measurements have also been performed.