Synthesis, structure and light scattering properties of tetraalkylammonium metal isothiocyanate salts

Abstract

A series of ammonium and tetraalkylammonium metal isothiocyanate salts of the type Q_y[M(NCS)_x] (M = Cr(III), x = 6, y = 3, Q = NH₄⁺, Me₄N⁺, Et₄N⁺, n-Bu₄N⁺; M = Mn(II), x = 6, y = 4, Q = Me₄N⁺; M = Mn(II), x = 5, y = 3, Q = Et₄N⁺; M = Fe(III), x = 6, y = 3, Q = Me₄N⁺, Et₄N⁺, n-Bu₄N⁺; M = Co(II), x = 4, y = 2, Q = n-Bu₄N⁺; M = Eu(III), Gd(III), Dy(III), x = 6, y = 3, Q = Bu₄N⁺) has been synthesized and structurally characterized. The octahedral Cr(III) salts are isostructural to previously and newly reported Fe(III) salts. The Ln(III)-containing anions are also octahedral. For Mn(II), although the Me₄N⁺ salt is octahedral, the Et₄N⁺ salt [Mn(NCS)₅]³⁻ possesses a distorted trigonal bipyramidal geometry. For (Et₄N)₃[Fe(NCS)₆] and (n-Bu₄N)₃[Fe(NCS)₆], a solid-state size-dependent change in colour from red to green was observed and was attributed to a light scattering phenomenon in the crystalline samples.