CONFORMATIONAL PROPERTIES OF EU(III) COMPLEXES OF 3,3'-5,3''-POLYMETHYLENE BRIDGED DERIVATIVES OF 2,2'-6,2''-TERPYRIDINE

The complex [Eu(tpy)3](ClO4)3, where tpy = 2,2'; 6,2''-terpyridine, ha s been prepared and reexamined. The complex appears to be stable in ac etonitrile solution with respect to decomplexation of the ligands but the addition of water does cause partial replacement of tpy. Analogous complexes have been prepared with 3,3'; 5,3''-polymethylene bridged d erivatives of tpy having two or three carbons in the bridge. The bridg ing enforces a cisoid geometry of the ligand and prohibits its replace ment by added water. An X-ray determination was carried out for [Eu(3b )3](ClO4)3, where 3b=3,3'; 5,3''-dimethylene tpy, which crystallizes i n the monoclinic space group P2(1)/c with a=11.908(4), b=15.768(5), c= 29.513(9) angstrom, beta=93.60(2)-degrees, mu=13.5 cm-1 and Z=4. The c omplex forms a tricapped trigonal prism with each of the ligands adopt ing the same dl conformation. Variable temperature NMR analysis of the bridged ligand complexes indicates that conformational inversion of t he bound ligand is not a concerted process and barriers for inversion of individual methylene units can be estimated from coalescence of the signals from the geminal methylene protons. The luminescence properti es of the bridged tpy complexes are similar to the parent unbridged sy stem.