Au₂(SeO₃)₂(SeO₄):  Synthesis and Characterization of a New Noncentrosymmetric Selenite−Selenate

Abstract

The reaction of elemental gold and selenic acid in Teflon-lined steel autoclaves leads to orange-yellow single crystals of Au2(SeO3)2(SeO4) (orthorhombic, Z = 4, Cmc2(1) (No. 36), a = 1689.1(3) pm, b = 630.13(8) pm, c = 832.7(1) pm, V = 886.2(2) angstroms3, Rall = 0.0452). In the crystal structure, Au3+ is surrounded by four oxygen atoms of just as many monodentate SeO3(2-) ions in a square planar manner. The linkage of the polyhedra leads to double chains in the [001] direction which are connected to puckered layers by SeO4(2-) groups. The noncentrosymmetric space group could be proved by the observation of an SHG effect upon irridation at 1064 nm that shows an efficiency of about 43% compared to a KDP reference. Upon heating, Au2(SeO3)2(SeO4) decomposes at about 370 degrees C in one step yielding elemental gold. The presence of selenite and selenate groups in the compounds is also obvious from the IR and Raman spectra which show the characteristic bands of both species. Furthermore, solid-state NMR spectra reveal the different surroundings of the selenium atoms in the compound.

Solid-state selenium-77 NMR

“…Recently, a mixed selenite-selenate gold complex, Au 2 (SeO 3 ) 2 (SeO 4 ), was synthesized and characterized by solid-state 77 Se NMR [217]. The 77 Se MAS NMR spectrum of Au 2 (SeO 3 ) 2 (SeO 4 ) displays two peaks in an approximate 2:1 intensity ratio, and determination of the two selenium chemical shift tensors indicates that the SeO 2À 4 anion is a highly distorted tetrahedron [217].…”

“…The 77 Se MAS NMR spectrum of Au 2 (SeO 3 ) 2 (SeO 4 ) displays two peaks in an approximate 2:1 intensity ratio, and determination of the two selenium chemical shift tensors indicates that the SeO 2À 4 anion is a highly distorted tetrahedron [217]. Ammonium hydrogen selenate, NH 4 HSeO 4 , has been the most studied selenium oxide system investigated by solid-state 77 Se NMR, primarily due to its complex phase behavior [218].…”

Square‐Planar Noble Metal Iodate [M(IO3)4]n– (M = PdII, AuIII; n = 2, 1) Anions and Their Ability to Form Polar and Centrosymmetric Architectures

“…[12] Renewed interest in noble metal oxoanion compounds has led to the discovery of a plethora of remarkable solids including AuSO 4 , which contains a Au II -Au II dimer, [13] and polar Au 2 (SeO 3 ) 2 (SeO 4 ), which is constructed from squareplanar Au III and both selenite and selenate anions. [14] Despite repeated attempts over the past eight years, gold iodates have remained elusive for several reasons. First, common anions employed in gold reactions such as chloride and nitrate can interfere with the formation of these compounds.…”

Extended networks, porous sheets, and chiral frameworks. Thorium materials containing mixed geometry anions: Structures and properties of Th(SeO3)(SeO4), Th(IO3)2(SeO4)(H2O)3·H2O, and Th(CrO4)(IO3)2

“…The structure of ThTe 2 O 6 has been solved using X-ray powder methods [13]. The selenite system is of particular interest because of the possibility of forming mixed-anion compounds containing both SeO 3 2-and SeO 4 2-[14], which was recently highlighted with the report of Au 2 (SeO 3 ) 2 (SeO 4 ) [15]. Given the high coordination numbers of Th and the presence of trigonal pyramidal and tetrahedral anions there is also the distinct possibility that these compounds might adopt acentric structures [16].…”