Multifrequency EPR Study and Density Functional g-Tensor Calculations of Persistent Organorhenium Radical Complexes

Abstract

The dinuclear radical anion complexes [(mu-L)[Re(CO)(3)Cl](2)](*)(-), L = 2,2'-azobispyridine (abpy) and 2,2'-azobis(5-chloropyrimidine) (abcp), were investigated by EPR at 9.5, 94, 230, and 285 GHz (abpy complex) and at 9.5 and 285 GHz (abcp complex). Whereas the X-band measurements yielded only the isotropic metal hyperfine coupling of the (185,187)Re isotopes, the high-frequency EPR experiments in glassy frozen CH(2)Cl(2)/toluene solution revealed the g components. Both the a((185,187)Re) value and the g anisotropy, g(1) - g(3), are larger for the abcp complex, which contains the better pi-accepting bridging ligand. Confirmation for this comes also from IR and UV/vis spectroscopy of the new [(mu-abcp)[Re(CO)(3)Cl](2)](o/)(*)(-)(/2)(-) redox system. The g values are reproduced reasonably well by density functional calculations which confirm higher metal participation at the singly occupied MO and therefore larger contributions from the metal atoms to the g anisotropy in abcp systems compared to abpy complexes. Additional calculations for a series of systems [(mu-abcp)[M(CO)(3)X](2)](*)(-) (M = Tc or Re and X = Cl, and X = F, Cl, or Br with M = Re) provided further insight into the relationship between spin density distribution and g anisotropy.

Relativistic two-component calculations of electronic g-tensor for oxo-molybdenum(V) and oxo-tungsten(V) complexes: The important role of higher-order spin-orbit contributions

“…DFT calculations have been done either at the generalized-gradient-approximation (GGA) level, with the Becke exchange and Perdew correlation functionals (BP86) [30][31][32], or employing Becke's three-parameter hybrid functional with Perdew-Wang GGA correlation (B3PW91) [33][34][35][36]. As in most of our previous studies on EPR parameters of transition metal complexes [26,27,[37][38][39][40][41][42][43][44] the best agreement with experimental data for both hyperfine and g-tensors was obtained with hybrid functionals containing approximately 30-40% Hartree-Fock exchange, we have also evaluated the use of the oneparameter BPW91-40HF functional of the form E hybrid…”

A complete series of tricarbonylhalidorhenium(I) complexes (abpy)Re(CO)3(Hal), Hal=F, Cl, Br, I; abpy=2,2′-azobispyridine: Structures, spectroelectrochemistry and EPR of reduced forms

“…Rhenium has two naturally occuring istopes: 185 Re (37.4% abundance; I = 5/2; a 0 = 1253.60 mT) and 187 Re (62.6%; I = 5/2; a 0 = 1266 mT). These are the largest isotropic hyperfine coupling constants a 0 of all transition metal elements [17,18], and since the total abundance is 100%, the coupling is clearly visible. The fluoride complex shows a more complicated hyperfine pattern than the other three analogues.…”

“…In frozen solutions at X-band frequency nearly isotropic signals were detected. The chemical sensitivity of these paramagnetic complexes precluded EPR measurements at very high frequencies which usually require ex situ radical generation [18].…”

Structure, electrochemistry, spectroscopy, and magnetic resonance, including high-field EPR, of {(μ-abpy)[Re(CO)3X]2}o/•−, where abpy=2,2′-azobispyridine and X=F, Cl, Br, I

“…With X = Cl and Br these compounds could be well characterized and also studied by advanced computational methods [16]. Since the mononuclear series (abpy)Re(CO) 3 X, X = F-I, was described previously [10], we have now investigated the dinuclear series (l-abpy)[Re(CO) 3 X] 2 , X = F, Cl, Br or I.…”

“…To study the influence of the halide on {(l-abpy)[Re(CO) 3 X] 2 } n , the following methods have been employed: 1 H NMR, EPR (particularly high-field EPR), X-ray crystallography, cyclic voltammetry, UV/Vis and IR spectroelectrochemistry. Relevant DFT calculation results [16] will be used for discussion.…”