Skeleton atomic effect on nonlinear optical properties of linear trinuclear heteroselenometallic compounds with univalent coinage metals

Abstract

Treatment of [NEt₄]₂[WSe₄] with 2 equiv. of [M(PPh₃)₂(NO₃)] (M = Cu or Ag) in CH₂Cl₂ gave the trinuclear cupro- or argento-selenotungstate compounds [(WSe₄)(MPPh₃){M(PPh₃)₂}] (M = Cu 1, Ag 2). In compounds 1 and 2, the [WSe₄]²⁻ anion is bonded to [M(PPh₃)]⁺ and [M(PPh₃)₂]⁺ fragments, resulting in trigonal and tetrahedral coordination geometries around M. Treatment of [NEt₄]₂[WSe₄] with [Au(PPh₃)Cl] in a 1:2 molar ratio afforded the trinuclear auroselenotungstate compound [WSe₄(AuPPh₃)₂] 3. For compound 3, the two equivalent [Au(PPh₃)]⁺ fragments bind to the [WSe₄]²⁻ symmetrically, and the geometry around the two Au atoms is distorted trigonal planar. Compounds 1–3 are air and optically stable. Their nonlinear optical absorption and refraction along with the optical limiting effects were determined under the same conditions. By comparison of nonlinear optical properties of the three compounds, a skeleton atomic effect on the nonlinear optical properties for heteroselenometallic cluster compounds was outlined. Compound 3 exhibits both large nonlinear optical absorption and refraction (self-focusing). The Ag-containing heteroselenometallic compound 2 may be considered as a good candidate for an optical limiting material.