What does ``through-bond coupling`` mean? Observations on simple donor-acceptor systems
- Wayne State Univ., Detroit, MI (United States). Dept. of Chemistry
A series of covalently linked, transition-metal donor/acceptor complexes are described in which the net donor-acceptor coupling matrix element, H{sub DA}, is independent of the extent of coupling between the donor and the bridging ligand. The bridging ligand in these complexes is a transition-metal dicyano complex with a tetraaza aliphatic nonbridging ligand, cis- or trans-M(MCL)(CN){sub 2}{sup +} for M = Rh(III), Co(III), or Cr(III), donor = Ru(NH{sub 3}){sub 5}{sup 2+}, and the acceptor = Ru(NH{sub 3}){sub 5}{sup 3+}. The electronic coupling (and electron delocalization) between the donor and the central atom (M) of the bridging ligand varies from H{sub DL} {approx} 10{sup 3} to {approximately}3 {times} 10{sup 3} cm{sup {minus}1} through the series of M(MCL)(CN){sub 2}{sup +}-bridged complexes, and this variation has an effect on the energy of the Ru(II)/Ru(III) CT absorption maximum, which is expected from perturbational mixing of these electronic states. However, the usually correlated superexchange contribution to H{sub DA} is not observed and appears to be less than about 10% of the contribution predicted. This is in contrast to observations on related complexes with pyridyl-type bridging ligands. The unusual behavior can be a consequence of the dependence of D/A electronic coupling on the CN{sup {minus}} vibrational distortions and the mixing of the two Ru(II)/Ru(III) electron-transfer states with the BL state promoted by in-phase and out-of-phase combinations of CN{sup {minus}} stretches. Such an approach predicts very little superexchange coupling when there is little electron dislocalization onto the bridging ligand and requires that H{sub DA} be a strong function of the electron-transfer coordinates.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 655332
- Journal Information:
- Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory, Journal Name: Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory Journal Issue: 39 Vol. 102; ISSN 1089-5639; ISSN JPCAFH
- Country of Publication:
- United States
- Language:
- English
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