Spectroscopic studies of gallium complexes in solution: Multinuclear NMR and raman spectra of mixed-ligand halidethiocyanate and halide etherate complexes

Abstract

High-field 71Ga NMR spectra at 122.03 MHz of aqueous Ga 3+ solutions containing NCS − ions show the progressive replacement of the sharp signal of [Ga(H 2O) 6] 3+ by a broad up-field resonance due a mixture of gallium thiocyanate complexes. Solvent extraction into diethyl ether or methyl isobutyl ketone phases is employed to prepare and identify a series of four-coordinate gallium complexes, including [Ga(NCS) 4] −, [GaN n (NCS) 4 − n ] − (X = Cl, Br of I) and [GaX m Y n (NCS) 4 − m − n ] − (in which X and Y are different halide ligands). The method of pairwise interactions is used to calculate the chemical shifts and lends support to the assignments. Vibrational frequencies derived from Raman spectra and the 71Ga, 14N and 13C NMR chemical shifts of these species are reported. [Ga(NCS) 4] − is characterized by a 71Ga resonance at 125 ppm, 14N resonance at −257 ppm (MeNO 2 scale) and v(GaNCS) sym = 318 cm −1. Two of the species, [GaCl 3NCS] − and [GaCl 2(NCS) 2] −, exhibit GaN coupling which is observed in both 71Ga and 14N NMR spectra as 1 J(Ga 14N) = 97 and 112 Hz, respectively. The 71Ga NMR spectra of gallium halide etherates, GaX n Y 3 − n ·OEt 2 (X and Y = Cl, Br or I; n = 0–3), have been observed in the range 242 to −220 ppm and consist of much broader signals than those of the complex anions, reflecting the low symmetry and other influences of the different kinds of ligands.