Comparative X-ray and 27Al NMR spectroscopic studies of the speciation of aluminum in aqueous systems: Al(III) complexes of N(CH2CO2H)2(CH2CH2OH)

Abstract

It is recognized that many aspects of the aqueous chemistry of AlIII and FeIII are similar and this might explain how aluminum is able to enter organisms. Since aluminum is potentially toxic, it is important to be able to characterize its speciation in solution. Three major difficulties are the existence of a large number of equilibrium processes, its ready hydrolysis, and the lack of suitable spectroscopic probes. One way of looking directly at the aluminum environment is by 27Al NMR, but there are difficulties with spectral assignment. A comparison of solid-state structures determined by X-ray crystallography with these NMR spectra offers a means of determining which species are important components in the solution state. With this in mind, we have synthesized and characterized by X-ray crystallography two new aluminum complexes and used the information from the synthetic procedure and the structural details to interpret 27Al NMR. These components are directly analogous to the iron compounds reported by us previously. They are a dinuclear compound [Al(heidi)(H2O)]2·2H2O and a tridecanuclear compound [Al13μ(3-OH)6 μ(2-OH)12(heidi)6(H2O)6]3+. © 1995.