The Creutz-Taube complex revisited: a single-crystal EPR study

Abstract

Single-crystal EPR experiments have been performed on orthorhombic [(NH3)5Ru(pz)Ru(NH3)5]Cl5'5H20 at 3 K. Two resonance lines appear in the crystallographic ab plane, one each from the two structurally equivalent binuclear ions with different orientation. The resonances are described by g tensors that have their principal axes collinear to the molecular axes. Both gx components are parallel to the crystallographic c axis, which is perpendicular to the plane of the pyrazine rings. The angle between the Z axes (Ru-Ru line) of the two magnetically inequivalent complexes is 86 (1)°i n agreement with X-ray diffraction results (85.5°). The components of the g tensor are gx = 1.346 (3), gY -2.799 (3), and gz = 2.487 (3). No Ru hyperfine structure could be observed owing to the large line width in the undiluted single crystal. The EPR spectrum was simulated by diagonalization of the 6 X 6 perturbation matrix using a one-center basis set in the hole formalism with the parameters D/\ -2.317 (20), E/\ = 0.745 (20), and K = 0.981 (5). Both an axial and a rhombic component of the ligand field must be considered to reproduce the g tensor anisotropy. The orbital reduction factor k within the t2g5 configuration is estimated to be 0.79. The unpaired electron is predominantly in an orbital perpendicular to the plane of the pyrazine ring. Delocalization of the odd electron over the two ruthenium ions via the tr* system of the pyrazine ring is therefore possible.

Strong metal–metal coupling in mixed-valent intermediates [Cl(L)Ru(μ-tppz)Ru(L)Cl]+, L = β-diketonato ligands, tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine

“…The almost equal spin distribution calculated for the ruthenium ions in 1 + or 3 + suggests a delocalised mixed- valent situation, as supported by the high K c values of 10 10 -10 12 (Table 4). The g anisotropies in 1 + -5 + (Δg: 0.99-0.82, Table 5) are smaller than that reported for the Creutz-Taube ion (Δg = 1.445), 12 which implies the participation of the bridging and unsaturated ancillary ligands in the spin accommodation. The first oxidation (Ox1) potential decreases slightly with increasing +I-effect of the substituents, Me < Et < t Bu, in the acac − -type ligands of 1, 2, and 3, respectively, accompanied by the smaller HOMO-LUMO energy separation of 3 (1.68 eV) as compared to that of 1 (1.87 eV) (Fig.…”

Mixed‐Valence Ruthenium Complexes Rotating through a Conformational Robin–Day Continuum

“…No attempt has been made here to include counter ions in the structural models but it can be assumed that some screening of charge is affected by the continuum-solvent treatment. Compound [3] 5+ has probably been investigated more extensively than any other MV complex, through detailed experimental measurements in the solid state [56][57][58] and in solution, [26,59,60] and also using quantum-chemical methods. [61][62][63][64][65][66] The UV-vis-NIR spectrum of [3] 5+ exhibits a single asymmetric band envelope with no notable shoulders (preventing simple Gaussian fitting).…”

Stark spectroscopy of mixed-valence systems

“…EPR data show increasing g-anisotropy as the electron accepting character of R increases. Since MVCs involving Ru(III) are expected to show large g-anisotropies due to spin-orbit coupling (Stebler et al 1984;Khan et al 1990), this trend has been interpreted as a shift from a bridgecentred to a metal-centred unpaired electron (Kasack et al 1995). The compounds in which RZaryl or alkyl have near-IR absorption bands with similar bandshapes to that of the Creutz-Taube ion.…”