%0 Journal Article %1 Farrell.2001 %A Farrell, I. R. %A Hartl, F. %A Zalis, S. %A Wanner, M. %A Kaim, W. %A Vlcek, A. %D 2001 %J Inorganica Chimica Acta %K carbonyl chromium complex electrooxidn phenanthroline spectroelectrochem %N 1,2 %P 143--151 %R 10.1016/S0020-1693(01)00421-2 %T Electrochemical oxidation of Cr(CO)4(tmp) to the low-spin Cr(I) species Cr(CO)4(tmp)+ (tmp=3,4,7,8-tetramethyl-1,10-phenanthroline): An IR, UV-Vis, and EPR spectroelectrochemical and DFT computational study of the accompanying changes in molecular and electronic structure %V 318 %X The complexes Cr(CO)4(phen) and Cr(CO)4(tmp) (phen=1,10-phenanthroline, tmp=3,4,7,8-Me4-phen) are electrochem. oxidized at -0.01 and -0.05 V vs. Fc/Fc+ to the corresponding cations. The oxidn. is electrochem. reversible and chem. nearly reversible at room temp. and a scan rate of 1000 mV s-1. The cation Cr(CO)4(tmp)+ is chem. stable at 193 K but undergoes a complete loss of CO ligands at higher temps. It was characterized by EPR, IR, and UV-Vis spectroelectrochem. at 193 K and its structure and bonding have been investigated by d. functional theory (DFT) calcns. It follows that Cr(CO)4(tmp)+ can be described as a Cr(I) complex with a low-spin d5 electron configuration. The EPR spectrum shows a g-anisotropy (g‖-g$\bot$) of 0.1, which is characteristic of a metal-centered radical. Oxidn. is accompanied by a large shift of electron d. toward the Cr atom, manifested by nearly a 100 cm-1 shift of the n(CO) IR bands to higher frequencies on oxidn. Moreover, the IR spectrum of Cr(CO)4(tmp)+ suggests that the stretching force consts. of the axial and equatorial CO ligands become nearly equal upon oxidn. and their interaction strengthens. DFT calcns. have revealed that Cr(CO)4(tmp)+ has three low-lying electronic states, which are very close in energy. Each of these states can be the electronic ground state. They differ in the symmetry of the singly occupied MO, which, in each case, has a predominant Cr 3d character. While the spin d. is localized mostly on the Cr atom, the charge on Cr is nearly the same in the neutral and in the cationic complexes. The charges on the CO ligands and, to a lesser extent, on tmp become more pos. upon oxidn., due to electron-d. redistribution. Lengthening of the Cr-C bonds and shortening of C$\equiv$O and Cr-N bonds are the main calcd. structural changes caused by the oxidn. of Cr(CO)4(tmp). Oxidn. of the analogous W complexes is chem. irreversible on the cyclic voltammetry time scale at room temp., reflecting the high reactivity of W(CO)4(tmp)+ and W(CO)4(phen)+. on SciFinder(R)

@article{Farrell.2001, abstract = {The complexes [Cr(CO)4(phen)] and [Cr(CO)4(tmp)] (phen=1,10-phenanthroline, tmp=3,4,7,8-Me4-phen) are electrochem. oxidized at -0.01 and -0.05 V vs. Fc/Fc+ to the corresponding cations. The oxidn. is electrochem. reversible and chem. nearly reversible at room temp. and a scan rate of 1000 mV s-1. The cation [Cr(CO)4(tmp)]+ is chem. stable at 193 K but undergoes a complete loss of CO ligands at higher temps. It was characterized by EPR, IR, and UV-Vis spectroelectrochem. at 193 K and its structure and bonding have been investigated by d. functional theory (DFT) calcns. It follows that [Cr(CO)4(tmp)]+ can be described as a Cr(I) complex with a low-spin d5 electron configuration. The EPR spectrum shows a g-anisotropy (g‖-g$\bot$) of 0.1, which is characteristic of a metal-centered radical. Oxidn. is accompanied by a large shift of electron d. toward the Cr atom, manifested by nearly a 100 cm-1 shift of the \textgreek{n}(CO) IR bands to higher frequencies on oxidn. Moreover, the IR spectrum of [Cr(CO)4(tmp)]+ suggests that the stretching force consts. of the axial and equatorial CO ligands become nearly equal upon oxidn. and their interaction strengthens. DFT calcns. have revealed that [Cr(CO)4(tmp)]+ has three low-lying electronic states, which are very close in energy. Each of these states can be the electronic ground state. They differ in the symmetry of the singly occupied MO, which, in each case, has a predominant Cr 3d character. While the spin d. is localized mostly on the Cr atom, the charge on Cr is nearly the same in the neutral and in the cationic complexes. The charges on the CO ligands and, to a lesser extent, on tmp become more pos. upon oxidn., due to electron-d. redistribution. Lengthening of the Cr-C bonds and shortening of C$\equiv$O and Cr-N bonds are the main calcd. structural changes caused by the oxidn. of [Cr(CO)4(tmp)]. Oxidn. of the analogous W complexes is chem. irreversible on the cyclic voltammetry time scale at room temp., reflecting the high reactivity of [W(CO)4(tmp)]+ and [W(CO)4(phen)]+. [on SciFinder(R)]}, added-at = {2022-06-15T11:26:56.000+0200}, author = {Farrell, I. R. and Hartl, F. and Zalis, S. and Wanner, M. and Kaim, W. and Vlcek, A.}, biburl = {https://puma.ub.uni-stuttgart.de/bibtex/296d411e143770376706391431c30ad7e/huebleriac}, doi = {10.1016/S0020-1693(01)00421-2}, interhash = {e071fc0e17373279f3d47277f7048ef3}, intrahash = {96d411e143770376706391431c30ad7e}, issn = {0020-1693}, journal = {Inorganica Chimica Acta}, keywords = {carbonyl chromium complex electrooxidn phenanthroline spectroelectrochem}, number = {1,2}, pages = {143--151}, timestamp = {2022-06-15T09:26:56.000+0200}, title = {Electrochemical oxidation of [Cr(CO)4(tmp)] to the low-spin Cr(I) species [Cr(CO)4(tmp)]+ (tmp=3,4,7,8-tetramethyl-1,10-phenanthroline): An IR, UV-Vis, and EPR spectroelectrochemical and DFT computational study of the accompanying changes in molecular and electronic structure}, volume = 318, year = 2001 }