Metals 'talk' in 4f-5f complexes

Bridging ligands between metal centers in organometallic complexes are known to serve as conduits for the metal atoms to engage in d-d, d-f, and, in rare cases, f-f electron coupling, giving rise to potentially useful electronic and magnetic properties. Eric J. Schelter, David E. Morris, Jaqueline L. Kiplinger, and their coworkers at Los Alamos National Laboratory have now demonstrated examples of the first f-f electron coupling for lanthanide-actinide complexes (J. Am. Chem. Soc., published online Jan. 28, dx.doi.org/10.1021/ja057808+). The team synthesized the complexes by coupling thorium or uranium ketimide-terpyridine complexes to an ytterbocene complex. The uranium complex shown is one of only three known structurally characterized complexes containing both lanthanide (Yb = red) and actinide (U = green) metal ions; the ketimide ligands bound to uranium (U-N=CR-, R = benzyl) connect to the terpyridine ligand bound to each ytterbium atom (N = blue, C = gray). The "rich electrochemical behavior" of the complexes indicates that the 4f and 5f metals are electronically communicating, and the magnetic response of the uranium complex indicates U-Yb magnetic coupling at low temperatures, the researchers report.