The absorption spectra of RuII(NH3)5L and RuIII(NH3)5L (L is an aromatic N-heterocycle or nitrile) complexes in 50:50 glycerol−water glasses at 77 K (D s = 3.9) are a function of the applied field in the 106−107 V/m range. Analysis of the spectra in terms of the Liptay equations yields ground−excited state dipole-moment differences ranging from 4 to 37 D, depending upon the nature of L. The measured dipole moment differences, particularly those for the MLCT transitions, are much smaller than the values estimated from a simple consideration of the electron-transfer distances. The discrepancy between the observed and naive dipole-moment estimates arises mainly from the multielectron nature of the response to excitation. Good agreement is obtained with the predictions of a model which includes refinement of the effective electron-transfer distance, the shift in the valence electron distribution in the excited state, and the effects of electron delocalization (π-backbonding for Ru(II) and π-bonding for the Ru(III) complexes). Other contributions, namely the dipole moment induced by the NH3 ligands and by the surrounding solvent molecules, are also considered.

The reactivity of the previously (Organometallics 2000, 19, 824-833) prepared hydride complexes (C 5 H 4 CO 2 H)L(CO) 2 WH (L ) CO, PMe 3 ) and the corresponding metal-metal dimers [(C 5 H 4 CO 2 H)L(CO) 2 W] 2 in pulse radiolysis studies in aqueous solution is reported. The disappearance of e aqwas monitored to determine the rate constants for one-electron reduction. The smallest reduction rate constant was obtained for the dianion (C 5 H 4 CO 2 )-(CO) 3 W 2-(4.3 × 10 9 M -1 s -1 ), and the largest value (1.2 × 10 10 M -1 s -1 ) was observed for its conjugate acid (C 5 H 4 CO 2 )(CO) 3 WH -. For the PMe 3 -substituted complexes, the dimer reduction rate constant was about twice as large as that for the hydride (k ) 8.4 × 10 9 M -1 s -1 ). Rate constants for reaction with CO 2 -, 3.2 × 10 8 (pH 5) and 3.0 × 10 7 (pH 9.7) M -1 s -1 , were determined for (C 5 H 4 CO 2 )(CO) 3 WHand (C 5 H 4 CO 2 )(PMe 3 )(CO) 2 WH -, respectively. Rate constants for the reactions of the hydride complexes with the carbon-centered radical from tert-butyl alcohol and the R-hydroxy radicals from ethanol and 2-propanol radicals were in the ranges (0.9-4.8) × 10 8 and (0.3-0.6) × 10 8 M -1 s -1 for (C 5 H 4 CO 2 )(CO) 3 WHand (C 5 H 4 CO 2 )(PMe 3 )(CO) 2 WH -, respectively. The transient produced in all of these reactions was the metal radical, which was observed to dimerize with k ) 2.4 × 10 9 and 2.2 × 10 8 M -1 s -1 for (C 5 H 4 CO 2 )(CO) 3 WHand (C 5 H 4 CO 2 )(PMe 3 )(CO) 2 WH -, respectively.