Jean-Claude Bunzli - Structural and Photophysical Properties of Lanthanide Complexes with Planar Aromatic Tridentate Nitrogen Ligands As Luminescent Building-Blocks for Triple-Helical Structures

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  Piguet,C., Williams,A.F., Bernardinelli,G., Bunzli,J.C.G.   Inorganic Chemistry 1993 32  (19) 4139-15

  Abstract: The ligand   2,6-bis(1-methylbenzimidazol-2-yl)pyridine (mbzimpy, 1) reacts   with lanthanide perchlorate in acetonitrile to give the   successive complexes [Ln(mbzimpy)n]3+ (n = 1-3). Tris complexes   were isolated for La, Eu, Gd, and Tb, while a bis complex only   could be crystallized for Lu. The crystal structure of   [Lu(mbzimpy)2(H2O)(CH3-OH)] (ClO4)3.3CH3OH (12,   LuC46H52N10O17Cl3, a = 13.140(3) angstrom, b = 22.007(4)   angstrom, c = 18.927(7) angstrom, beta = 107.53(1)-degrees,   monoclinic, P2(1)/c, Z = 4) shows three uncoordinated ClO4-   anions and a [Lu(mbzimpy)2(H2O)(CH3OH)]3+ cation where Lu(III) is   eight-coordinated by two meridional tridentate mbzimpy ligands,   one methanol molecule, and one water molecule, leading to a   low-symmetry coordination sphere around the metal ion. The   crystal structure of [Eu(mbzimpy)3](ClO4)3 [6, EuC63H51N15O12Cl3,   a = 24.703(2) angstrom, c = 16.982(2) angstrom, trigonal, R3BAR,   Z = 6) shows a mononuclear cation [Eu(mbzimpy)3]3+ with C3   symmetry where Eu(III) is nine-coordinated by three tridentate   mbzimpy (1) which are wrapped around the metal ion to give an   approximate trigonal tricapped prismatic arrangement of the nine   nitrogen donor atoms leading to a pseudo-D3 symmetry.   Luminescence studies of crystalline [Eu(mbzimpy)3] (ClO4)3 (6)   confirm the high symmetry for the Eu(III) sites while H-1-NMR and   luminescence measurements in solution indicate that the   triple-helical structure of [Eu(mbzimpy)3]3+ is maintained in   acetonitrile. Spectrophotometric titrations show that the three   expected successive complexes [Ln(mbzimpy)]3+, [Ln(mbzimpy)2]3+,   and [Ln(mbzimpy)3]3+ are formed in solution for all the   lanthanide ions studied (Ln = La, Nd, Eu, Gd, Tb, Ho, Yb, Lu),   but that [Ln(mbzimpy)3]3+ complexes are significantly less stable   for the heavier lanthanides (Ln = Ho, Yb, Lu) and for the   tridentate ligands 2,6-bis(1-X-benzimidazol-2-yl)pyridine (X =   propyl, pbzimpy, 2; X = 3,5-dimethoxybenzyl, dmbbzimpy, 3] which   have bulky groups bound to the aromatic benzimidazole rings. The   origin of these effects is discussed together with the use of   these complexes as luminescent building blocks for the formation   of triple-helical structures

  Address (URL): WOS:A1993LY53100029

 

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