Na2B12Si6Se18: a novel B12-cluster-containing quaternary selenoborate framework material

Abstract

We report the successful synthesis of the new quaternary, three-dimensional Na₂Si₆B₁₂Se₁₈ material using a solid-state synthesis route. This compound is characterized by a unique framework structure that features the rare icosahedral [B₁₂]¹⁰⁺ cation which is connected via Si₂Se₆ polyhedral units into a 3D framework structure with Na⁺ ions located inside the channels. The Na₂Si₆B₁₂Se₁₈ compound crystallizes in the cubic crystal system in the space group Im, with lattice parameter a = 11.91110(10) Å and unit cell volume of 1689.88(4) ų. The 3D framework of the [Si₆B₁₂Se₁₈]²⁻ anion contains B₁₂ icosahedra with six of their edges bridged by tetrahedral SiSe₄ groups. The B₁₂ icosahedral units are connected by the SiSe₄ tetrahedral units which bridge between each B₁₂ icosahedron. Ultraviolet–Visible (UV-vis) spectroscopy revealed that Na₂Si₆B₁₂Se₁₈ exhibits semiconducting behavior with an estimated bandgap of 2.1(1) eV. In situ powder X-ray diffraction (PXRD) studies were conducted to investigate the phase formation of this compound as a function of temperature to obtain information of its thermal stability and structural evolution.