Jean-Claude Bunzli - Eu(III) Complexes of Tetradentate Ligands Related to 2,9-Di(pyrid-2 '-yl)-1,10-phenanthroline and 2,2 '-Bi-1,10-phenanthroline

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      Zong,R., Zhang,G., Eliseeva,S.V., Bunzli,J.C.G., Thummel,R.P.   Inorganic Chemistry 2010 49  (10) 4657-4664

      Abstract: A series of six tetradentate   polypyridine-type ligands (L) have been used to prepare the   corresponding Eu(III) complexes [Eu(L)(2)(S)(n+) (n = 2, 3) where   S = H(2)O or CF(3)SO(3)(-). Two of the ligands,   2,9-di(pyrid-2'-yl)-1,10-phenanthroline (4) and its   dipyridophenazine analogue (6) are symmetrical around a central   phenanthroline ring. The other four ligands are   2,2'-bi-1,10-phenanthroline and its 3,3'-di-, tri-, and   tetramethylene-bridged analogues (5a-d) whose conformations are   governed by the length of the polymethylene bridge. (1)H NMR and   X-ray analysis indicate that all of the complexes have a C(2v)   symmetry. The biphenanthroline series shows a strong correlation   of the conjugation between the two halves of the ligand, as   governed by the bridge, with the absorption and emission   properties of the Eu(III) complex. The complex having the most   distorted, tetramethylene-bridged ligand exhibits a weak, high   energy pi-pi* absorption and low sensitization efficiency. The   luminescence decays are monoexponential for complexes of 4 and   either monoexponential or biexponential for the complexes of 5   depending on its solution concentration and the length of the   bridge. The complexes of 4 exhibit much longer lifetime, higher   overall quantum yield, and higher sensitization efficiency than   complexes of 5 while the complex of 6 emits very weakly. The   Eu((5)D(0)) lifetime for [Eu(4)(2)(H(2)O)](ClO(4))(3) is shorter   than for [Eu(4)(2)(CF(3)SO(3))](CF(3)SO(3))(2), reflecting the   effect of the coordinated water. The complexes are examined for   stability in the presence of water and found to retain most of   their luminescent properties even in the presence of a large   excess of water

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