Crystal structures and luminescence spectra of ten-co-ordinate lanthanide(III) complexes (Ln = Ce, Sm, Eu or Tb) with 2,6-bis(benzimidazol-2-yl)pyridine

Abstract

The complexes [LnL₂(NO₃)₂]NO₃·nMeOH [L = 2,6-bis(benzimidazoi-2-yl)pyridme, Ln = Ce 1, n= 3; Ln = Eu 3 or Tb 4, n= 2] have been characterized by single-crystal X-ray diffraction, IR and ¹H 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 P, Z= 2: 1, a= 10.907(1), b= 14.498(1), c= 16.187(2)Å, α= 63.02(1), β= 75.54(1), γ= 74.54(1)°3, a= 10.864(8), b= 14.57(1), c= 15.95(1)Å, α= 116.92(8), β= 90.46(8), γ= 106.32(8)°4, a= 10.847(1), b= 14.567(2), c= 15.847(2)Å, α= 117.25(1), β= 90.39(1), γ= 106.37(1)°. 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→⁷F₂ and ⁵D₀→⁷F₄ are more intense than is the magnetic dipole transition ⁵D₀→⁷F₁, and the latter comprises three bands, suggesting a low C₁ symmetry for the Eu³⁺ ion, consistent with the crystallographic results.