SK-Edge XAS And DFT Calculations on Square-Planar NiII-Thiolate Complexes: Effects of Active And Passive H-Bonding

• Published in: Inorganic chemistry 2009-04, Vol.46 (23)
• Main Authors: Dey, A., Green, K.N., Jenkins, R.M., Jeffrey, S.P., Darensbourg, M., Hodgson, K.O., Hedman, B., Solomon, E.I., /Stanford U., Chem. Dept. /SLAC, SSRL /Texas A-M
• Format: Article
• Language: English
• Subjects: ABSORPTION SPECTROSCOPY; CHEM; CHEMICAL BONDS; COVALENCE; DENSITY FUNCTIONAL METHOD; HYDROGEN; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; NICKEL COMPOUNDS; ORGANIC SULFUR COMPOUNDS; X-RAY SPECTROSCOPY
• ISSN: 0020-1669; 1520-510X

S K-edge XAS for a low-spin Ni{sup II}-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 Fe{sup III}-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 Fe{sup III}-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 Ni{sup II}-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.