โ Scribed by A. Fratiello; V. Kubo-Anderson; E. Bolanos; O. Chavez; J. V. Ortega; R. D. Perrigan; A. Reyes; S. M. Stoll
No coin nor oath required. For personal study only.
A multinuclear magnetic resonance (NMR) study of the complexes of aluminum(III) with isothiocyanate ion in waterโacetone mixtures has been completed. At temperatures low enough to slow proton and ligand exchange, separate resonance signals are observed for coordinated and bulk H~2~O (^1^H) and NCS^โ^ (^13^C, ^15^N), and Al^3+^ (^27^Al) in each complex. The ^1^H NMR spectra reveal six sets of signals for the complexes, [Al(H~2~O)~6~]^3^+ through [Al(H~2~O)(NCS)~5~]^2โ^, including isomers for three of the species. Signal area measurements show a decrease in the Al^3^+ hydration number with increasing NCS^โ^ concentration, as this anion replaces water in the solvation shell. In the ^27^Al NMR spectra of these systems, signals for seven complexes, [Al(H~2~O)~6~]^3+^ through [Al(NCS)~6~]^3โ^, are observed, with chemical shifts increasing by about 6 ppm with each additional NCS^โ^. Although broadened somewhat by the Al(III) quadrupole, the ^13^C and ^15^N NMR spectra also reveal coordinated NCS^โ^ signals for these complexes, including ^27^Al๏ฃฟN^13^CS Jโcoupling in [Al(NCS)~6~]^3โ^. Area evaluations of the ^15^N NMR signals provide an excellent complement to the ^1^H hydration number data. These NMR results demonstrate that a multinuclear approach to the study of solution complexes can provide detailed structural information about the species being formed.
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