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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 20, Number 6
BKCSDE 20(6)
June 20, 1999 

Tautomeric Fluxional Process in Metal Complexes. Insight into Cobalt(III) and Pentamethylcyclopentadienylrhodium(III) Complexes of 2-Mercaptopyrimidine Ligand
Ok-Sang Jung, Yong Tae Kim, Yun Ju Kim, Jung-Kyoun Chon, Hee K. Chae
Studies have been carried out on the unusual molecular nonrigidity of CoⅢ(PymS)3 and Cp* RhⅢ(PymS)2(PymS:2-mercaptopyrimidine). The crystal structure of CoⅢ(PymS)3 approximates to an octahedral mer isomer with 4-membered N-Schelating fashion. For Cp*RhⅢ(PymS)2, one PymS ligand bonds to the rhodium ion in an S-monodentate mode (Rh-S(2) = 2.366(1)Å) while the other ligand chelates to the metal ion in an N,S-bidentae mode (Rh-S(1)=2.414(1);Rh-N(1)=2.103(3)Å). Even though the conformations and configurations of both complexes are still retained in solution, an unusual nonrigidity for the protons of the PymS region is obsered in the solution. The broad proton signals of CoⅢ(PymS)3 exhibit a temperature-dependence in the range of -40∼40℃ with a free energy of activation ΔG=64.49kJ/mol(40℃). For Cp*RhⅢ(PymS)₂,such a fluxionality has been markedly observed in solution. This fluxional behavior can be explained in terms of "ligand tautomerism" in metal complexes containing potential tautomeric forms.
648 - 652
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