Intermetallic communication

Let us focus on the photophysical intermetallic communication 2 resulting from intramolecular 4f —>4f energy transfer and whose global efficiency is given in Eq. (75). 

Intermetallic communication as a tool for tuning magnetic and photophysical properties... 

When one metal ion plays the role of a donor for sensitizing the emission of a second accepting metal ion, the characteristic lifetimes T of their excited states, which are related to their deactivation rates by em = ( em) / are affected by the intermetallic communication process (Figure 122). If the energy transfer rate is much faster than the deactivation rate of the donor ion, the situation is very simple and assuming a Forster s dipole-dipolar mechanism, the yield of the transfer is given similarly to Eq. (77) by... 

Modification of the ligand denticity (pentadentate instead of hexaden-tate) allows the assembly of nd-4f helicates which exhibit a rich variety of magnetic and spectroscopic properties combining the intrinsic features of both types of metal ions thanks to intermetallic communication within the helical molecules. The overview ends by describing helical structures foimd in coordination polymers, as well as some 5f helicates. 

Although the mechanism takes place exclusively at one of the metal sites, the ligand at the spectator iridium center occupying the position trans to the bridging hydride (L) effectively influences the catalytic activity of the binuclear system. Therefore, the intermetallic communication and, consequently, the binuclear nature of the complex play a crucial role on the performance of the catalyst even when the second metal is not directly involved in the catalytic cycle (Fig. 4). 

Felner, I., I. Mayer, A. Grill and M. Schieber, 1975, Solid State Commun. 16, 1005. landelli, A. and A. Palenzona, 1979, Crystal Chemistry of Intermetallic Compounds, in Handbook on the Physics and Chemistry of the Rare Earths, vol. 2, eds. K.A. Gschneidner, Jr. and L. Eyring (North-Holland, Amsterdam) p. 1. 

Intermetallic compounds are usually not among the first choice of novel catalytic materials. Besides being widely unknown, they are normally synthesized by a heat treatment of the appropriate amounts of the metallic elements in inert atmosphere, resulting in limited specific surface areas. Only very recently nanostruc-tured intermetallic compounds became available by industrially feasible routes, making these interesting materials available to the catal3dic community (8,9). 

---