EPR investigations of electron transfer in one-electron reduced α-1,4 K5[PV2W10O40].3H2O

Abstract

Heteropoly blues of α-1,2 and α-1,4 isomers of [PV 2 W 10 O 40 ] 5have been prepared by using the electrochemical technique. EPR spectra, measured as a function of temperature over a wide range (20-300 K), are explicable in terms of electronhopping processes in heteropoly blues. Temperature dependence of A || of the isomers suggest that the activation energy for electron hopping is greater for the α-1,4 isomer than the α-1,2 isomer. Other parameters like stability of the blues and intra-molecular electron transfer rate constants are also evaluated using EPR as the tool.

Studies on electron transfer reactions of Keggin-type mixed addenda heteropolytungstovanadophosphates with NADH

“…At room temperature the unpaired electron will be interacting equally with the two adjacent vanadium nuclei ( 51 V, I = 7/2, 100%) by a thermally activated hopping process 26 and this leads to 15 line pattern in the EPR spectrum at room temperature. The EPR spectrum of the reduction product obtained in the present study is similar to the EPR spectrum of one electron reduced HPB prepared by controlled potential electrolysis [26][27][28] …”

Directed Self‐Assembly, Symmetry Breaking, and Electronic Modulation of Metal Oxide Clusters by Pyramidal Heteroanions

“…[43,52,54] This makes the electron transfer extremelyf acile, and dependent on the V-O-V angle.F or Lindqvist ions, in which all octahedrala re edgeshared, the process is limited because the average 1258 angle is not optimal for d p -p p -d p overlap through which the unpaired electron in the vanadyl d xy orbital can transfer to an adjacent V V center. [52,53,56] At room temperature a1 5-lines pectrum is observedf rom coupling of the electron spin to two equivalent 51 Vn uclei, both as ap olycrystalline material and in solution. [52,47,50,53,54,56,69] At lower temperatures, and depending on the connectivity of the POM, the electron becomes localized.F or example, the electron in [PV 2 W 16 O 62 ] 9À is localized at 211K as the vanadium ions occupy edge-shared sites on the M 3 cap.…”

“…[52,53,56] At room temperature a1 5-lines pectrum is observedf rom coupling of the electron spin to two equivalent 51 Vn uclei, both as ap olycrystalline material and in solution. [52,47,50,53,54,56,69] At lower temperatures, and depending on the connectivity of the POM, the electron becomes localized.F or example, the electron in [PV 2 W 16 O 62 ] 9À is localized at 211K as the vanadium ions occupy edge-shared sites on the M 3 cap. [52] In contrast,i n corner-shared, mixed-valent V V /V IV moieties connected through more obtuse V-O-V angles up to 1508, [65] the unpaired electron is still delocalized to the adjacent V V ion down to 10 K. [53,70] Interestingly,p rotonation of one bridging oxo ligand destroys the efficiency of the d p -p p -d p overlapinasimilarmanner to positioning ag roup 6i on between V IV and V V ions.…”

“…Each cluster gives as ignal consistent with V IV ions with the spectrum dominated by hyperfine coupling to the 51 Vn ucleus (I = 7 / 2 ,9 9.75 % natural abundance)g enerating the hallmark 8-line pattern. The appearance of the hyperfine structure can range from an axially-split 15-line pattern [44,[45][46][47][48][49][50][51] to ab roadened 8-line spectrum [13,52,[53][54][55][56] to ac ompletely isotropic profile [41,57,58] depending on the POM, the number of V IV ions, andt heir position in the cluster. However, it is mostly the sample (polycrystalline or frozen solution) and measurement conditions (temperature, frequency) that dictate the final outcome of EPR experiments.…”

“…The bulk of the signal has spin-Hamiltonian parame-ters dissimilar to the classic vanadyl and are commonlye ncountered in mixed-valence systemsi nw hich more than one vanadium ion is presenti nb oth the + IV and + Vo xidation states. [43,44,52,46,47,50,51,53,54,56,63] The driving force behindt he reduced g-anisotropy and broad lines comesf rom electron hopping from the donor V IV centers to adjacent acceptor V V ions. The V IV !V V IVCT transition is found in the near-infraredr egion of the spectrum, below 9000 cm À1 .…”