Theory of adiabatic hexaamminecobalt self-exchange

We have reexamined the thermally induced Co(NH3)62+/3+ [Co(II/III)] redox reaction using the first-principles density-functional-theory method, semiclassical Marcus theory, and known charge transfer parameters. We find support for a previously suggested mechanism involving the excited state (2Eg) of Co(II) which becomes lower than the ground state (4T1g) in the transition state region. This lowers the transition-state barrier considerably by ∼6.9 kcal/mol and leads to a spin-allowed and adiabatic electron exchange process. Our calculations are consistent with previous experimental results regarding the spin-excitation energy (3T1g) of Co(III) and the fact that an optical absorption peak (2Eg) of the Co(II) species could not be found experimentally. Our rate is of order 6×10−3 (M s)−1 and hence two orders of magnitude faster than determined previously by experiments.

[1]  N. Sutin.  Theory of electron transfer reactions: insights and hindsights , 2007 .

[2]  A. Lichtenstein.  First-principles calculations of electronic structure and spectra of strongly correlated systems: the LDA+U method , 2006 .

[3]  David A Johnson,et al.  Ligand Field Stabilization Energies of the Hexaaqua 3+ Complexes of the First Transition Series. , 1999, Inorganic chemistry.

[4]  D. Sánchez-Portal,et al.  LINEAR-SCALING AB-INITIO CALCULATIONS FOR LARGE AND COMPLEX SYSTEMS , 1999, cond-mat/9904159.

[5]  Burke,et al.  Generalized Gradient Approximation Made Simple. , 1996, Physical review letters.

[6]  Robert G. Parr,et al.  Density Functional Theory of Electronic Structure , 1996 .

[7]  Bradley A. Smith,et al.  HOW DO DIFFERENT FLUORINE SUBSTITUTION PATTERNS AFFECT THE ELECTRONIC STATE ENERGIES OF PHENYLNITRENE , 1996 .

[8]  Car,et al.  First principles study of photoelectron spectra of Cun- clusters. , 1995, Physical review letters.

[9]  C. Cramer,et al.  AB INITIO CHARACTERIZATION OF PHENYLNITRENIUM AND PHENYLCARBENE : REMARKABLY DIFFERENT PROPERTIES FOR ISOELECTRONIC SPECIES , 1994 .

[10]  Martins,et al.  Efficient pseudopotentials for plane-wave calculations. , 1991, Physical review. B, Condensed matter.

[11]  O. Sankey,et al.  Ab initio multicenter tight-binding model for molecular-dynamics simulations and other applications in covalent systems. , 1989, Physical review. B, Condensed matter.

[12]  R. O. Jones,et al.  The density functional formalism, its applications and prospects , 1989 .

[13]  M. Zerner,et al.  Hexaamminecobalt electron-self-exchange reaction , 1986 .

[14]  M. Newton.  Comparison of electron-transfer matrix elements for transition-metal complexes: t2g vs. eg transfer and ammine vs. aqua ligands , 1986 .

[15]  Michael C. Zerner,et al.  Calculated spectra of hydrated ions of the first transition-metal series , 1986 .

[16]  R. Marcus,et al.  Electron transfers in chemistry and biology , 1985 .

[17]  H. Taube,et al.  Redetermination of the hexaaminecobalt(III/II) electron-self-exchange rate , 1984 .

[18]  Steven G. Louie,et al.  Nonlinear ionic pseudopotentials in spin-density-functional calculations , 1982 .

[19]  Leonard Kleinman,et al.  Efficacious Form for Model Pseudopotentials , 1982 .

[20]  G. Navon.  A search for the thermally populated high-spin excited state of hexaaquocobalt(3+) by coblt NMR , 1981 .

[21]  M. Dwyer,et al.  Crystal and molecular structure and vibrational and nuclear quadrapole resonance spectra of hexaamminecobalt(III) pentachloromercurate(II), [Co(NH3)6][HgCl5] , 1981 .

[22]  Bruce S. Brunschwig,et al.  A semiclassical treatment of electron-exchange reactions. Application to the hexaaquoiron(II)-hexaaquoiron(III) system , 1980 .

[23]  E. Solomon,et al.  Spectroscopic studies of photochemically important transition metal excited states. 2. The /sup 1/T/sub 1g/, /sup 3/T/sub 1g/, and /sup 5/T/sub 2g/ excited states of hexaamminecobalt(III) , 1980 .

[24]  G. Navon,et al.  The hexaamminecobalt electron-exchange reaction , 1979 .

[25]  B. Lundqvist,et al.  Exchange and correlation in atoms, molecules, and solids by the spin-density-functional formalism , 1976 .

[26]  K. D. Gailey,et al.  Natural circular Dichroism of Co(H2O)62+ and Cu(H2O)62+ in a Chiral Lattice , 1972 .

[27]  J. Ibers,et al.  Effect of metal-ligand bond distances on rates of electron-transfer reactions. Crystal structures of hexaammineruthenium(II) iodide, [Ru(NH3)6]I2, and hexaammineruthenium(III) tetrafluoroborate, [Ru(NH3)6][BF4]3 , 1971 .

[28]  J. Ibers,et al.  The Co(III)–N bond length in relation to the Co(II)–N bond length. The crystal structure of hexaamminecobalt(III) iodide [Co(NH3)6]I3 , 1969 .

[29]  M. L. Morrell,et al.  A STUDY OF NICKEL(II) AND COBALT(II) PHOSPHATE COMPLEXES , 1964 .

[30]  Rudolph A. Marcus,et al.  On the theory of oxidation—Reduction reactions involving electron transfer. V. Comparison and properties of electrochemical and chemical rate constants , 1963 .

[31]  F. P. Dwyer,et al.  THE RATE OF ELECTRON TRANSFER BETWEEN THE TRIS- (ETHYLENEDIAMINE)-COBALT(II) AND COBALT(III) IONS , 1961 .

[32]  J. Grossman,et al.  Exchange of Radiocobalt between the Hexammines of Cobalt(II) and Cobalt(III) in Liquid Ammonia , 1958 .

[33]  W. F. Libby.  Theory of Electron Exchange Reactions in Aqueous Solution , 1952 .

[34]  Clarence Zener,et al.  Dissociation of Excited Diatomic Molecules by External Perturbations , 1933 .

[35]  Peter Fulde,et al.  Electron correlations in molecules and solids , 1991 .

[36]  M. Newton.  The hexaammine cobalt (2+/3+) exchange reaction: ground-state versus thermally excited pathways , 1991 .

[37]  B. Brunschwig,et al.  Configuration changes in electron-exchange reactions of metal complexes , 1982 .

[38]  D. R. Stranks,et al.  Kinetics of isotopic exchange reactions. Part 7.—Electron exchange between cobaltic hexammine and cobaltous ammines , 1962 .

[39]  D. R. Stranks.  Mechanisms of some electron exchange reactions , 1960 .