Short Covalent Bridges

A set of bipy-based Ru /Os binudear complexes, comprising compounds 21-23 (Fig. 2.13), was prepared such that the energy gap between triplet states localized on donor and acceptor units remained at ca. 0.34 eV [112]. These complexes differed in the site of attachment of the acetylene bridge and used both ethynylene and butadiynylene connectors. Of course, with such systems it is difficult to be definitive about the exact nature of the bridge. It was found, however, that intramolecular triplet energy transfer was extremely fast in each case. There was htde 

This system was the first artificial prototype to exhibit switching between dipole-dipole and electron-exchange mechanisms [114]. 

In contrast to all other reported Ru poly(pyridine)-porphyrin dyads, complex 26 shows efficient singlet-singlet energy transfer from the second excited singlet state localized on the porphyrin to the MLCT state of the Ru complex (Fig. 2.16) [115], 

This process has the effect of prolonging the triplet lifetime of the Os complex [131]. 

---

Bridged polysilsesquioxanes having covalently bound acidic groups, introduced via modification of the disulfide linkages within the network, were studied as solid-state electrolytes for proton-exchange fuel cell applications.473 Also, short-chain polysiloxanes with oligoethylene glycol side chains, doped with lithium salts, were studied as polymer electrolytes for lithium batteries. 

A number of M(/i-H) M systems are known. These necessarily have both a bent M—H—M arrangement and, in view of the small covalent radius of H, a short M—M distance. Such systems also occur in metal clusters, e.g. the intensively studied Os3H2(CO)10. A strongly unsymmetrical bridge has been observed in [(dpe)Pt(/i-H)2PtH(dpe)]+ by neutron diffraction.8... 

---