Jean-Claude Bunzli - Luminescent properties of lanthanide nitrate complexes with substituted bis(benzimidazolyl)pyridines

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  Petoud,S., Bunzli,J.C.G., Schenk,K.J., Piguet,C. Inorganic   Chemistry 1997 36 (7) 1345-1353

  Abstract: The protonated form of the ligand   2,6-bis(1'-methylbenzimidazol-2'-yl)pyridine crystallizes as its   perchlorate salt (HL(1))ClO4 (1) in the orthorhombic system Pbca,   with a = 13.976(3) Angstrom, b = 14.423(3) Angstrom, c =   19.529(4) Angstrom, Z = 8. The proton is located on one   benzimidazole N-atom, and the two N-methyl substituents lie on   the same side of the pyridine N-atom (cisoid conformation). New   1:1 nitrate complexes of composition [Eu(NO3)(3)(L')]-(solv')(y)   have been isolated with L(4) (4), L(6) (5), L(7) (6), and L(8)   (7), and their structural and photophysical properties are   compared with those of the previously reported complexes   [Eu(NO3)(3)(L(1))(MeOH)] (2) and [Eu(NO3)(3)(L(3))] (3). The   crystal and molecular structure of [Eu(NO3)3(L(7))(MeCN)]. 2.5   MeCN at 180 K (6a, triclinic, P (1) over bar, a = 12.137(2)   Angstrom, b = 14.988(3) Angstrom, c = 16.926(3) Angstrom, alpha =   114.52(3)degrees, beta = 98.28(3)degrees, gamma =   103.99(3)degrees, Z = 2) shows a decacoordinated Eu-III ion to   six O-atoms from the nitrates, three N-atoms from L(7), and one   N-atom from a coordinated MeCN. The metal-centered luminescence   arising upon ligand excitation in the solid state is analyzed in   terms of nephelauxetic effects of the ligand and crystal field   splitting of the F-7(1) level. Quantum yields of 10(-3) and   10(-4) M solutions in MeCN are substituent dependent and may be   rationalized by taking into account several factors, including   the energy of the ligand singlet and triplet levels and the   arrangement of the ligands in the first coordination sphere. We   also show that the quantum yield of the ligand-centered   luminescence decreases in the order L(1) >   [La(NO3)(3)(L(1))]MeOH > [La(L(1))(3)](ClO4)(3)

  Address (URL): WOS:A1997WQ49000011