Synthesis, crystal structure and properties of a new noncentrosymmetric tetraoxidomolybdate(VI)

Abstract

An attempted exchange of ammonium cations in (NH sub(4)) sub(6)[M sub(o7)O sub(24)].6H sub(2)O by reaction with tris(hydroxymethyl)aminomethane (tris) resulted in the serendipitous formation of a mixed cationic tetraoxidomolybdate(VI) viz. (NH sub(4))(trisH)[MoO sub(4)] 1. The spectral and thermal characteristics, solution conductivity study and the single crystal structure of 1 are reported. The presence of the tetrahedral [MoO sub(4)] sup(2-) unit is confirmed by the characteristic Raman spectrum. Compound 1 crystallizes in the noncentrosymmetric trigonal space group P3c1 with both the unique cations and the [MoO sub(4)] sup(2-) dianion located on a three-fold axis. The cations and the anion are interlinked with the aid of O-H...O, N-H...O and C-H...O interactions. The strength and number of O...H contacts affect the Mo-O bond distances. Compound 1 exhibits a piezoelectric effect, which is comparable with that of alpha-quartz. Irradiation of 1 with 1064 nm laser light results in a second harmonic generation (SHG) output which is twice that of potassium dihydrogen phosphate (KDP). Thermal decomposition of 1 results in the formation of orthorhombic alpha-MoO sub(3).