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Numerous heteropoly anions1™4 can be reduced by addition of various numbers of electrons. The reduction products, which typically retain the general structures of their oxidized parents5 and are frequently deep blue in color, comprise a potentially important large group of complexes generally known as the "heteropoly blues". The added ("blue") electrons are "delocalized", according to various time scales, over certain atoms and/or regions

The kinetics of photoinduced electron-transfer (ET) reactions have been measured in a series of synthetic donor-acceptor complexes. The electron donors are singlet or triplet excited iridium(I) dimers (Ir(2)), and the acceptors are N-alkylpyridinium groups covalently bound to phosphinite ligands on the Ir(2) core. Rate constants for excited-state ET range from 3.5 x 10(6) to 1.1 x 10(11) per second, and thermal back ET (pyridinium radical to Ir(2)(+)) rates vary from 2.0 x 10(10) to 6.7 x 10(7) per second. The variation of these rates with driving force is in remarkably good agreement with the Marcus theory prediction of a Gaussian free-energy dependence.

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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