Paramagnetic transition-metal carbonyls and cyanides. Part III. Electron spin resonance studies of manganese pentacarbonyl halides after high-energy irradiation

Abstract

Exposure of the manganese pentacarbonyl halides [Mn(CO)5X] (X = CI, Br or I), to 6oCo y-rays a t 77 K givas an S = centre having a g ca. 2 and a large hyperfine coupling to 65Mn and the halogen nuclei. The results are interpreted in terms of electron addition into a cs* orbital involving mainly the metal d, a and halide pz orbitals. A second centre having two apparent g values in the g = 6 region is also formed for all the three complexes. These again exhibit hyperfine coupling to 55M and to the halogen nuclei. Various structures are considered, and it is concluded that the most reasonable are cations formed by loss of an electron and one or more carbonyl groups with unpairing of the remaining electrons to give S = g.

Density Functional Theory Calculations on 19-Electron Organometallic Complexes: The Mn(CO)5Cl- Anion. The Difference between Unpaired Electron Density and Spin Density Due to Spin Polarization

“…The EPR researchers also expressed some doubt about the sign of the total hfc constants for chlorine. , In ref the possibilities considered were (46.2, 21.6, 20.0) and (46.2, −21.6, −20.0), for which the isotropic couplings are calculated to be 29.3 and 1.5 G, respectively . Both EPR research groups favored all positive signs .…”

“…The EPR experiments were carried out using two different matrixes. In one study, a single crystal of Mn(CO) 5 Cl was irradiated with γ-rays, while in the other study, Mn(CO) 5 Cl was doped into Cr(CO) 6 and then irradiated. In the more polar medium (Mn(CO) 5 Cl), the hfc to Mn is greater and the hfc to Cl is smaller than in the less polar Cr(CO) 6 matrix (Table ).…”

“…They are based either on the reasonableness of calculated orbital populations for 1 or by comparison to hyperfine data for molecular halogen anions. See refs and .…”

“…To check on the generality of the results obtained in our CpCo(CO) 2 - study 1 (namely that many 19-electron complexes have considerably less metal character than attributed to them by EPR), we carried out calculations on the Mn(CO) 5 Cl - molecule, a putative 19-electron complex obtained by γ-irradiation of Mn(CO) 5 Cl in either a single crystal or in a Cr(CO) 6 matrix at low temperature. An additional goal of this study was to find out if DFT calculations could determine if it was Mn(CO) 5 Cl - or Mn(CO) 4 Cl - that was observed in the EPR experiments.…”

Investigation of organometallic reaction mechanisms with one and two dimensional vibrational spectroscopy

“…For example, Mn(CO) 5 Cl − was generated by γ-irradiation of Mn(CO) 5 Cl, studied both computationally [132] and experimentally [133,134] and found to be better described as a 19 rather than 18+δ-electron complex. In condensed phase organometallic chemistry, however, 19e species are, in general, generated by coordination of a 2-electron donor with a 17e radical:…”