Structural and photoluminescent studies of lanthanide complexes with tripodal triRNTB (N-substituted tris(benzimidazol-2-ylmethyl)amine): ligand substituent, anionic and secondary ligand effects.

Six N-substituted NTB ligands (NTB = (tris(benzimidazol-2-ylmethyl)amine), namely, triMeNTB (L1), triEtNTB (L2), triPrNTB (L3), triBuNTB (L4), triAlNTB (L5) and triBzNTB (L6), have been synthesized through replacing the H atoms on the NH groups by methyl, ethyl, (n)propyl, (n)butyl, allyl, and benzyl groups, respectively. Their corresponding Sm(3+), Eu(3+) and Tb(3+) complexes consisting of different anions or secondary ligands have been prepared and characterized by elemental analyses, IR spectra and single-crystal X-ray diffraction measurements. Three types of structural models have been obtained: (2) where two triTNTB ligands wrap around the Ln(3+) ion with anions (ClO(4)(-) and CF(3)SO(3)(-)) free of coordination, (3) where one triRNTB ligand holds the Ln(3+) ion with anions (Cl(-), NO(3)(-) and picrate) participating in coordination, and '(3) where one triNTB ligand and three secondary antipyrine ligands coordinate with the Ln(3+) ion. The Ln(3+) ions in (2) type complexes are 8-coordinating and display a slightly distorted cubic (LnN(8)) coordination geometry. The Ln(3+) ions in (3) and '(3) types complexes show two different coordination geometries: one is 7-coordinating ((3) with Cl(-) anion and '(3)), which can be described as a severely distorted cube short of one corner (LnN(4)Cl(3) or LnN(4)O(3)), and the other is 10-coordinating ((3) with NO(3)(-) and picrate anions) which can be regarded as a severely distorted cube with one corner substituted by a three-atom cap (LnN(4)O(6)). The photoluminescent study reveals that the complexes with different Ln(3+) ions show a general luminescent intensity tendency of Tb > Eu > Sm. The modification of the NTB molecule by altering R groups tunes the triplet states of the ligands and results in differentiable photophysical properties of the complexes. The anions or secondary ligand also have remarkable effects on the luminescent properties of the complexes.