Platinum Metals Chemistry Research Group, Department of Chemistry and Polymer Science, University of Stellenbosch, P Bag X1, Matieland, South Africa
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; Tel: ++2721 808 3020
Dalton Trans., 2012,41, 10533-10542
04 Jun 2012,
12 Jul 2012
First published online
12 Jul 2012
At high magnetic fields the 128.8 MHz 195Pt NMR of all the species in the series [PtCln(H2O)6−n]4−n (n = 2–6) display unique 35/37Cl isotope effects resulting in a unique ‘fine-structure’ of each individual resonance, which constitutes an unambiguous spectroscopic ‘fingerprint’ characteristic of the structure of the octahedral platinum(IV) complex, provided 195Pt NMR are recorded at optimum magnetic field homogeneity and carefully controlled temperature (293 ± 0.1 K). The detailed 195Pt resonance fine-structure observed experimentally can readily be accounted for by an isotopologue and isotopomer model for each complex, showing particularly noticeable differences between stereoisomer pairs such as the cis/trans- and fac/mer-complexes. Moreover partial isotopic 18O enrichment of the coordinated water molecules in the series [Pt35/37Cln(H216/18O)6−n]n−2 (n = 2–6) confirms this model. This technique can thus be considered a novel, direct spectroscopic method of chemical speciation of appropriate platinum(IV) complexes in solution without reference to accurate chemical shifts of authentic members of such a series. These effects are interpreted qualitatively in terms of the high sensitivity of 195Pt NMR shielding to very small and subtle Pt–35/37Cl and Pt–16/18OH2 bond displacements. Preliminary work shows this also applied to the corresponding bromido-complexes.
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