Complex EPR spectrum

A complex EPR spectrum detected (47) in the y-irradiated Vahrenkamp molecule Mn2 (CO) 8(/i-AsPh2) 2 is thought to belong to the cation of the molecule. From an analysis of the 55Mn and 75As hyperfine structure it was concluded that the d6d5 dimer radical has its single unpaired electron in a o MO composed of Mn 3(1 2 y2 orbitals. 

The complex EPR spectrum of O J adsorbed on SnOz has received another interpretation by Anufrienko et al. (22f, 187), who assign the various peaks... 

Adsorption of N2 (100 Torr) at low temperature onto the MgO electron rich surface gives rise to a complex EPR spectrum which has been assigned to a surface N2 radical ion The spectrum in Fig. la has been interpreted using the following spin-Hamiltonian ... 

The radical anion of 6 was first observed by Sondheimer [87] and recently by Stevenson [88]. The main conclusion from these studies is that the structure is nonplanar, because of a Jahn-Teller distortion. The large total spectral width in the radical anion indicates that the carbons with negative spin densities contribute extensively to the coupling. The complex EPR spectrum eliminates the possibility of pseudo rotation on the EPR time scale, which could lead to uniform spin densities. The rotation is prevented by the nonplanarity of the radical anion. 

Of the 24 lines expected for coupling between V (I =7/2) and two equivalent C (I = V ) nuclei, 18 were resolved in the epr spectrum of VO(S CNEt2)2, showing that the C(2s) orbital can also participate in transannular interactions (61). [Cp2V(S2CNEt2)BF4] and dithiophos-phate have been used in an extension of studies on the C4V oxovana-dium(IV) chelates to yield C2V bis(cyclopentadienyl) complexes. 

Transannular interaction via the electron-delocalization mechanism was found, but lessened by 10-15% for the ligand superhyperfine splitting and 30-35% for the hyperfine splitting (62) in the epr spectrum. The crystal structure of [VOS2CNEt2)2] shows that the molecular core has the expected C2V symmetry [V-0 = 159.1(4), V-S = 138.7(2)-241.0(2) pm] (63). Magnetic and spectral data provided evidence for a tetragonal, pyramidal structure (VII) for these complexes. Like many other coordinatively unsaturated, metal... 

In the Me2dtc complex, a unique, 15-line, epr spectrum was reported (69) that was peculiar only to the tetraphenylborate salt. This suggests a V-V interaction in the lattice. Electrochemical studies on these [CpjVLJ complexes (L = dithiocarboxylato ligand) shows two well defined, polarographic, reduction waves, and, for the process at most positive potential, the reversible formation of a V(III) species was postulated (72-74). 

The second distinguishing feature of the Rieske protein apart from its unique EPR spectrum that was recognized early is its high redox potential 91). The redox potentials of Rieske clusters from mitochondrial and bacterial bci complexes are in the range of +265 to + 310 mV (Table XI) the potentials in complexes are even slightly... 

A decade after the discovery of the Rieske protein in mitochondria (90), a similar FeS protein was identified in spinach chloroplasts (91) on the basis of its unique EPR spectrum and its unusually high reduction potential. In 1981, the Rieske protein was shown to be present in purified cytochrome Sg/complex from spinach (92) and cyanobacteria (93). In addition to the discovery in oxygenic photosynthesis, Rieske centers have been detected in both single-RC photosynthetic systems [2] (e.g., R. sphaeroides (94), Chloroflexus (95)) and [1] (Chlo-robium limicola (96, 97), H. chlorum (98)). They form the subject of a review in this volume. 

Cationic ferrocene complexes with one, two, and four cationic [B(R)bpy] (bpy = 2,2,-bipyridine) acceptors such as 66 show absorption at Amax = 496-540 nm with the contribution of charge transfer between the ferrocene unit and the B(R)bpy substituent(s) (165). This is confirmed by the EPR spectrum of the monoreduced neutral species, which features a line shape indicating a considerable admixture of the ligand and metal orbitals. Preparation and physical properties of the related polymer, 67, have also been reported (166). 

The synthesis, structure, and electrochemistry of Ir1 dinuclear complexes [Ir(/i-L)(cod)]2 (L = 2-aminopyridinato (ap) and 2-anilinoj)yridinato (anp)) are reported, in which the square-planar Ir1 centers are 3.0998 A and 3.0681 A apart, respectively.511 Both complexes may be reversibly oxidized to the mixed-valent species. The frozen EPR spectrum of the mono-oxidized anp species shows a rhombic signal with no resolved hyperfine splitting. 

The interest in low-valent Ni complexes in S-rich environments has been stimulated by the presence of Ni in [Ni,Fe] hydrogenase and CODH. While thiolate ligation usually favors higher oxidation states, thioethers stabilize Ni1 and Ni°. In most cases, however, Ni1 ions of an NiS4 chromophore are unstable with respect to disproportionation. The cyclic voltam-mogram of square planar (983) with homoleptic thioether coordination exhibits a quasi-reversible wave at —0.42V (vs. NHE), which on the basis of the rhombic EPR spectrum (gi 2.27, g2 2.11, and g3 2.03) of the chemically reduced species (Na/Hg) is assigned to metal-centered reduction. 8... 

The Ni1 complex (996) has been structurally characterized. It displays an axial EPR spectrum and an intense //(CO) band at 2,026cm. 131, 1317... 

In their pursuit of modeling Type I copper proteins, Kitajima et al. reported112 a rare, tetrahedrally coordinated complex (105), which displayed an EPR spectrum consistent with the presence of the unpaired electron in the dz2 orbital.1 They also isolated a square-pyramidal DMF adduct (complex (106)). They were successful in providing structural proof of a copper(II) complex (trigonal pyramidal) with C6F5S -coordinated complex (107), with CuN3S chromo-phore.113 The X-ray analysis (poor data set) of a closely similar complex with Ph3CS as the... 

---