NMR of phosphorus-31 heteroatoms in paramagnetic 1-electron heteropoly blues. Rates of intra- and intercomplex electron transfers. Factors affecting line widths

Abstract

s), 1218 (s), 1200 (s), 1180 (s), 1158 (s), 890 (s), 750 (m), 710 (m), 690 (m), 610 (m), and 590 (s) cm-I; NMR (CDC13) 6 6.83 (m, b) ppm. neering Research Council of Canada, Ottawa, for generous financial support and Dr. A. McAuley for valuable suggestions. Acknowledgment. We thank the Natural Sciences andAbstract: Heteropoly complexes are increasingly used as catalysts and specialized redox reagents, making knowledge of electron-exchange characteristics important. Relatively sharp 31P NMR signals (v112 = 1-15 Hz) are observed at rwm temperature from the heteroatoms in paramagnetic one-electron heteropoly blue reduction products of a-[PWI2O4,$-and a-[P2wl@62]6-in aqueous solution. Line broadenings for equimolar mixtures of the reduction products and their isostructural oxidized parent heteropoly complexes enable calculation of rates of exchange of the delocalized electrons between each reduced complex and its oxidized isomorph. These exchange rates correspond exactly to diffusion-controlled rates for the a-1 8-tungstodiphosphates and for the a-12-tungstophosphates, although the rate for the former, larger complex is 3 orders of magnitude slower than for the latter. The similarly evaluated electron-exchange rate between a-[P2M03W15062]b and its one-electron reduction product, wherein the added electron is delocalized over the three Mo atoms in one end of the ellipsoidal complex, is an order of magnitude slower than that calculated for diffusion control, probably owing to necessity for contact between the Mo,O,, caps of the exchanging complexes. Extents of broadenings of the two 31P NMR lines of le blue al-[P2MoW17062]7-and its a2 isomer show that the 31P atoms' relaxation mechanism is essentially purely dipolar. Thus, intracomplex exchange rates can be calculated from line widths for electrons hopping among the 12 belt W atoms in (Y-[P2W&2]'-and among the 3 cap Mo atoms in a-[P2M03W15062]7-. Electron hopping in the latter isomorph is -25 times slower than in the former.Abstract: A metal complex, (3,4-diacetyl-2,5-hexanedionato)bis[(2,2',2''triaminotriethylamine)cobalt(II1)] ion, was prepared and optically resolved. T h e optical resolution of the complex confirmed the expected novel twin structure and presented a

Ionic-strength dependence of electron-transfer reactions of Keggin heteropolytungstates: Mechanistic probes of O2 activation in water

“…As in self-exchange between 1 1e and 1 ox [8,20], electron transfer between ␣-2 1e and ␣-2 ox obeys the following rate expression [17]:…”

Molybdophosphate heteropoly blues: Electron-transfer reactions in aqueous solutions as studied by NMR

“…Paramagnetic one-electron blues (I) were predominantly studied by ESR spectroscopy [7,[26][27][28][29][30], while diamagnetic two-(II) and four-electron (IV) blues were observed in solutions by NMR spectroscopy [31][32][33]. However, paramagnetic H 4 [PW 12 O 40 ] (I) in dilute aqueous solution was found to give a sharp 31 P NMR peak shifted only a little downfield relative to that of nonreduced H 3 [PW 12 O 40 ] (0) [34,35]. The peak was strongly broadened and shifted in the presence of the nonreduced HPA (0) because of electron self-exchange [PW 12 O 40 ] 3À/4À , which allowed the rate of the electron transfer reaction to be determined.…”

Electron Transfer Behavior of Multi‐Iron Sandwich‐Type Polyoxometalates and Electrocatalytic Reduction Reactions

“…Introduction of lower symmetry results in a variation in the degree of valence trapping. [10,11,13] Unlike the spherical α-Keggin anion, the WellsϪDawson structure ( Figure 1B) is shaped like a prolate ellipsoid, [16] consisting of six ''cap'' tungsten centers and twelve ''belt'' tungsten centers. The non-equivalence of the ''cap'' and ''belt'' tungsten sites raises the issue of the initial site of the electron transfer.…”