Intrinsic Cl and O isotope shifts in Pt and Rh NMR of purely inorganic Pt and Rh complexes as unique spectroscopic fingerprints for unambiguous assignment of structure.

Well-resolved intrinsic ΔM(Cl) and ΔM(O) isotope shifts (where M = Pt or Rh) are visible in the Pt NMR peak profiles of relatively kinetically inert [PtCl(HO)] (n = 1-6) complexes, their corresponding hydroxido [PtCl(OH)] (n = 1-5/6) anions, and [RhCl(HO)] (n = 3-6) complexes in aqueous solutions at ca. 293 K. Although some such isotope effects have been previously reported, there are very limited published data in the open literature, and the first systematic studies of such intrinsic ΔM(Cl) and ΔM(O) isotope effects are reviewed in this perspective. In high magnetic-field NMR spectrometers, the Pt and Rh NMR peak profiles acquired within a relatively narrow temperature range (288-300 K) constitute unique 'spectroscopic fingerprints', which allow unambiguous structural assignment in solution. Available data for Pt(iv) and Rh(iii) complexes give rise to intrinsic isotope ΔδPt/Rh(Cl) profiles, which are extraordinarily sensitive to the structure of a particular complex or its geometric isomer. The profiles of aquated Pt(iv) and Rh(iii) complexes in acidic solutions may be resolved at either an isotopologue level only or at both an isotopologue and an isotopomer level depending on the structure. By contrast, in the series of [PtCl(OH)] (n = 1-6) anions, ΔδPt(Cl) isotope shifts are resolved only at an isotopologue level. Relatively larger ΔPt(O) isotope shifts obtained by the partial O enrichment of both the [PtCl(HO)] (n = 1-6) and [PtCl(OH)] (n = 1-6) series give rise to remarkable Pt NMR peak profiles showing both Cl and O shifts. In the [PtCl(OH)] (n = 1-5/6) anions a typical NMR peak profile spanning ∼2 ppm only may be resolved at both the isotopologue and isotopomer levels, depending on whether OH ions are coordinated trans to chloride ions or not. The potential utility of such ΔPt(Cl) and ΔPt(O) isotope shifts in selected practical applications involving such complexes is briefly illustrated.