Electronic structure of the ferricenium cation. Electron spin resonance measurements of the cations of ferrocene derivatives
TL;DR: In this article, the E.S.R. spectra of substituted ferrocenes have been measured at 20° and 77°k, respectively, and it has been shown that Fe(C5H5)2 + has the orbitally degenerate 2 E 2g [(e 2g )3(a 1g 2 ] ground state configuration.
Abstract: E.S.R. spectra of cations of substituted ferrocenes have been measured at 20° and 77°k. The g values are highly anisotropic, with g ¶ = 4·35 and g⊥=1·26 for Fe(C5H5)2 +. Owing to a fast spin-lattice relaxation the E.S.R. signals are much broader and less intense at 77° than at 20°k. A theoretical analysis shows that Fe(C5H5)2 + has the orbitally degenerate 2 E 2g [(e 2g )3(a 1g 2 ] ground-state configuration. The combined action of the spin-orbit interaction H so and a low-symmetry perturbation H 1 splits the fourfold degenerate level into two Kramers doublets. Since H so and H 1 are of the same order of magnitude, the orbital momentum contribution to the g values is only partly quenched and the g values deviate strongly from the free-electron value. The predicted splitting of the Kramers doublets is small and this explains the fast relaxation. The e 2g molecular orbitals are essentially localized on the iron atom. Substitution influences primarily the symmetry of the complex; it has no great influence on...
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TL;DR: In this article, the electronic structures of the first-row transition metal metallocenes, MCp2 (M = V, Cr, Mn, Fe, Co, and Ni), have been studied using a broad range of density functional methods with flexible double-ζ plus polarization (DZP) basis sets.
Abstract: The electronic structures of the first-row transition-metal metallocenes, MCp2 (M = V, Cr, Mn, Fe, Co, and Ni), have been studied using a broad range of density functional methods with flexible double-ζ plus polarization (DZP) basis sets. Geometrical parameters of the D5h and D5d conformations (and structures of lower symmetry for CrCp2 and CoCp2) were fully optimized. For the ferrocene system, best characterized experimentally, the B3LYP, BLYP, and BP86 methods give structures in good agreement with experiment. For the D5h−D5d energy difference, the same three methods predict 0.75 kcal/mol (B3LYP), 0.99 kcal/mol (BLYP), and 1.13 kcal/mol (BP86). The cyclopentadienyl rings are very nearly planar; the angles of the C−H bond out of the Cp ring are less than 1° for all metallocenes except ferrocene. The C−H bonds are bent slightly away from the metal for V and Mn, slightly toward the metal for Fe and Ni, and virtually not at all from chromocene. According to the energetic and vibrational analyses, the D5h co...
156 citations
TL;DR: In this paper, it was shown that the ferricenium cation FeCp+2 is stable in acetonitrile, acetone and nitromethane, but it is decomposed by Cl− and Br− to FeC p+2 and FeX−4 and by DMF, DMSO, HMPTA, o-Phen and Bipy to FeP2 and an FeII complex, octahedrally coordinated by the added donor molecules.
155 citations
01 Jan 2002
TL;DR: In this paper, a review of electron spin relaxation times for organic radicals and transition metal ions in magnetically dilute samples is presented, focusing on studies that have been performed as a function of temperature and that provide insight into the relaxation processes.
Abstract: Review of electron spin relaxation times for organic radicals and transition metal ions in magnetically dilute samples. Emphasis is placed on studies that have been performed as a function of temperature and that provide insight into the relaxation processes.
149 citations
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TL;DR: In this article, it was shown that isotropic (or average) nuclear resonance shifts for a nucleus in a paramagnetic molecule in solution, and in a polycrystalline solid, can be used to distinguish between Fermi contact and pseudocontact contributions.
Abstract: It is shown that isotropic (or average) nuclear resonance shifts for a nucleus in a paramagnetic molecule in solution, and in a polycrystalline solid, can be used to distinguish between Fermi contact and ``pseudocontact'' contributions to isotropic nuclear‐hyperfine interactions. The pseudocontact interaction is that isotropic hyperfine coupling which arises from the combined effects of (electron‐spin)‐(nuclear‐spin) coupling, (electron‐orbit)‐(nuclear‐spin) coupling, and electron spin‐orbit interaction. When the magnetic hyperfine interaction between the electronic moment and nuclear spin is approximated by a point dipolar interaction, and the isotropic hyperfine interaction is exclusively pseudocontact, then the isotropic nuclear shift in a polycrystalline solid exceeds the solution shift by the factor 3(g∥+g⊥)/(g∥+2g⊥) where g∥ and g⊥ are the spectroscopic splitting factors parallel and perpendicular to the molecular symmetry axis. Isotropic shifts due to the Fermi contact interaction are the same for both solid state and solution cases.
669 citations
TL;DR: In this paper, it was shown that the dynamical Jahn-Teller effect in a complex having orbital degeneracy may partially quench spin-orbit interaction, the orbital parts of the Zeeman and hyperfine interactions, and other orbital operators governing response to perturbations such as strain or applied electric fields.
Abstract: It is shown that the dynamical Jahn-Teller effect in a complex having orbital degeneracy may partially quench spin-orbit interaction, the orbital parts of the Zeeman and hyperfine interactions, and other orbital operators governing response to perturbations such as strain or applied electric fields. Such dynamical quenching thus decreases the value of orbital reduction factors usually attributed in paramagnetic resonance studies to covalent bonding, without necessarily causing anisotropy in the spectrum of an individual complex. The dynamical Jahn-Teller effect may also substantially enhance various second-order effects. Such dynamic effects thus may make important changes in the parameters of the spin Hamiltonian without changing its symmetry. It is shown that the dynamical Jahn-Teller effect accounts qualitatively for unusual features in the spectra of interstitial transition-metal ions ${\mathrm{Cr}}^{0}$, ${\mathrm{Mn}}^{+}$, ${\mathrm{Mn}}^{0}$, and ${\mathrm{Fe}}^{+}$ in silicon and that it is probably of importance equal to or greater than that of covalent bonding in the interpretation of the spectrum of ${\mathrm{Fe}}^{2+}$ in MgO and CaO. A mathematical analysis of the dynamical effects is given for an orbital triplet state in interaction with a doublet or triplet vibrational mode, and some results are given also when the coupling is with the phonon continuum.
597 citations
TL;DR: In this paper, the matrix elements of spin-orbit interaction were obtained for polyatomic molecules using M.O. wave functions, taking account of configurational interaction, and the results were then applied to the calculation of singlet-triplet transition probabilities in aromatic compounds.
Abstract: The matrix elements of spin‐orbit interaction are obtained for polyatomic molecules using M.O. wave functions, taking account of configurational interaction. These results are then applied to the calculation of singlet‐triplet transition probabilities in aromatic compounds. It is shown without evaluation of integrals that intercombination transitions in these compounds should be much weaker than in most other classes of organic compounds. This is in agreement with experimental results on the phosphorescence lifetimes of these compounds.
490 citations