CRYSTAL-STRUCTURES AND LUMINESCENCE SPECTRA OF 10-CO-ORDINATE LANTHANIDE(III) COMPLEXES (LN = CE, SM, EU OR TB) WITH 2,6-BIS(BENZIMIDAZOL-2-YL)PYRIDINE

The complexes [LnL2(NO3)2]NO3.nMeOH [L = 2,6-bis(benzimidazol-2-yl)pyridine, Ln = Ce 1. n = 3; Ln = Eu 3 or Tb 4, n = 2] have been characterized by single-crystal X-ray diffraction, IR and H-1 NMR spectroscopy and molar conductivity. They are ten-co-ordinate with six nitrogen atoms from two tridentate L ligands and four oxygen atoms from two bidentate nitrates, crystallizing in the triclinic system, space group P1BAR, Z = 2: 1, a = 10.907(1), b = 14.498(1), c = 16.187(2) angstrom, alpha = 63.02(1), beta = 75.54(1), gamma = 74.54(1)-degrees; 3, a = 10.864(8), b = 14.57(1), c = 15.95(1) angstrom, alpha = 116.92(8), beta = 90.46(8), gamma = 106.32(8)-degrees; 4, a = 10.847(1), b = 14.567(2), c = 15.847(2) angstrom, a = 117.25(1), beta = 90.39(1), gamma = 106.37(1)-degrees. The luminescence spectra of complexes 2 (Ln = Sm), 3 and 4 were recorded at room temperature in the solid state, and the quantum yields measured in methanol solution were in the order Eu > Tb > Sm. In the luminescence spectrum of complex 3, the electric dipole transitions 5D0 --> F-7(2) and 5D0 --> F-7(4) are more intense than is the magnetic dipole transition 5D0 --> F-7(1), and the latter comprises three bands, suggesting a low C, symmetry for the Eu3+ ion, consistent with the crystallographic results.