K W Hipps - Single Molecule Imaging of Oxygenation of Cobalt Octaethylporphyrin at the Solution/Solid Interface: Thermodynamics from Microscopy

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      Publication Details (including relevant citation   information):

      Friesen, Benjamin A., Bhattarai, Ashish, Mazur, Ursula, Hipps, K.   W. Journal of the American Chemical Society  2012 134 (36) 14897-14904

      Abstract: For the first time, the pressure and   temperature dependence of a chemical reaction at the   solid/solution interface is studied by scanning tunneling   microscopy (STM), and thermodynamic data are derived. In   particular, the STM is used to study the reversible binding of O2   with cobalt(II) octaethylporphyrin (CoOEP) supported on highly   oriented pyrolytic graphite (HOPG) at the phenyloctane/CoOEP/HOPG   interface. The adsorption is shown to follow the Langmuir   isotherm with P1/2298K = 3200 Torr. Over the temperature range of   10–40 °C, it was found that ΔHP = −68 ± 10 kJ/mol and ΔSP = −297   ± 30 J/(mol K). The enthalpy and entropy changes are slightly   larger than expected based on solution-phase reactions, and   possible origins of these differences are discussed. The big   surprise here is the presence of any O2 binding at room   temperature, since CoOEP is not expected to bind O2 in fluid   solution. The stability of the bound oxygen is attributed to   charge donation from the graphite substrate to the cobalt,   thereby stabilizing the polarized Co–O2 bonding. We report the   surface unit cell for CoOEP on HOPG in phenyloctane at 25 °C to   be A = (1.46 ± 0.1)n nm, B = (1.36 ± 0.1)m nm, and α = 54 ± 3°,   where n and m are unknown nonzero non-negative integers.

      Address (URL): http://dx.doi.org/10.1021/ja304431b