GaSeCl₅O: A Molecular Compound with Very Strong SHG Effect

Abstract

GaSeCl₅O is a new inorganic molecular compound prepared from SeO₂, SeCl₄, and GaCl₃ at 50 °C in quantitative yield. The structure of the title compound is described by GaCl₃(OSeCl₂) molecules with a tetrahedrally coordinated Ga atom and a pseudo-tetrahedrally coordinated Se atom (including lone pair of Se(IV)) that are bridged by oxygen. GaSeCl₅O crystallizes in the polar chiral space group <i>P</i>6₁, which is rarely observed for molecular structures. The compound is characterized by X-ray structure analysis based on single crystals and powder samples, thermogravimetry, infrared and Raman spectroscopy as well as by second harmonic generation (SHG) measurements. The experimental data are complemented by density functional theory calculations. GaSeCl₅O shows one of the strongest SHG signals known in the visible part of the electromagnetic spectrum (480-700 nm) with an SHG intensity 10 times higher than potassium dihydrogen phosphate (KDP). This is in accordance with the phase matchability and a strong dipole moment (|<b>μ</b>| = 8.3 D for a molecule in the crystal lattice). Such a strong SHG effect is also remarkable since GaSeCl₅O-unlike most of the materials with strong SHG intensity-is an inorganic molecular compound.