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S K-Edge XAS and DFT Calculations on Square-Planar NiII−Thiolate Complexes:  Effects of Active and Passive H-Bonding

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journal contribution
posted on 12.11.2007, 00:00 by Abhishek Dey, Kayla N. Green, Roxanne M. Jenkins, Stephen P. Jeffrey, Marcetta Darensbourg, Keith O. Hodgson, Britt Hedman, Edward I. Solomon
S K-edge XAS for a low-spin NiII−thiolate complex shows a 0.2 eV shift to higher pre-edge energy but no change in Ni−S bond covalency upon H-bonding. This is different from the H-bonding effect we observed in high-spin FeIII−thiolate complexes where there is a significant decrease in Fe−S bond covalency but no change in energy due to H-bonding (Dey, A.; Okamura, T.-A.; Ueyama, N.; Hedman, B.; Hodgson, K. O.; Solomon, E. I. J. Am. Chem. Soc. 2005, 127, 12046−12053). These differences were analyzed using DFT calculations, and the results indicate that two different types of H-bonding interactions are possible in metal−thiolate systems. In the high-spin FeIII−thiolate case, the H-bonding involves a thiolate donor orbital which is also involved in bonding with the metal (active), while in the low-spin NiII−thiolate, the orbital involved in H-bonding is nonbonding with respect to the M−S bonding (passive). The contributions of active and passive H-bonds to the reduction potential and Lewis acid properties of a metal center are evaluated.