35Cl/37Cl isotope effects in 103Rh NMR of [RhCl(n)(H2O)(6-n)](3-n) complex anions in hydrochloric acid solution as a unique 'NMR finger-print' for unambiguous speciation.

A detailed analysis of the (35)Cl/(37)Cl isotope effects observed in the 19.11 MHz (103)Rh NMR resonances of RhCl(n)(H(2)O)(6-n) complexes (n=3-6) in acidic solution at 292.1K, shows that the 'fine structure' of each (103)Rh resonance can be understood in terms of the unique isotopologue and in certain instances the isotopomer distribution in each complex. These (35)Cl/(37)Cl isotope effects in the (103)Rh NMR resonance of the Rh(35/37)Cl(6) species manifest only as a result of the statistically expected (35)Cl/(37)Cl isotopologues, whereas for the aquated species such as for example Rh(35/37)Cl(5)(H(2)O), cis-Rh(35/37)Cl(4)(H(2)O)(2) as well as the mer-[Rh(35/37)Cl(3)(H(2)O)(3)] complexes, additional fine-structure due to the various possible isotopomers within each class of isotopologues, is visible. Of interest is the possibility of the direct identification of stereoisomers cis-RhCl(4)(H(2)O)(2), trans-RhCl(4)(H(2)O)(2), fac-[RhCl(3)(H(2)O)(3)] and mer-[RhCl(3)(H(2)O)(3)] based on the (103)Rh NMR line shape, other than on the basis of their very similar δ((103)Rh) chemical shift. The (103)Rh NMR resonance structure thus serves as a novel and unique 'NMR-fingerprint' leading to the unambiguous assignment of RhCl(n)(H(2)O)(6-n) complexes (n=3-6), without reliance on accurate δ((103)Rh) chemical shifts.