Syntheses, characterization and crystal structures of 5,14-dihydro-6,8,15,17-tetramethyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecine rare earth(III) complexes

Abstract

Rare earth(III) complexes of tmtaa, Ln(tmtaa)(Htmtaa)·0.6CH₂Cl₂ (Ln = Pr 1, Nd 2, Sm 3, Gd 4, Tb 5, Er 6 and Yb 7; H₂tmtaa = 5,14-dihydro-6,8,15,17-tetramethyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecine) were prepared by reaction of Li₂tmtaa with LnCl₃(THF)₃ in tetrahydrofuran (THF). The complexes were characterized by infrared, mass and electronic spectra as well as DSC measurement. The crystal structures of Ln(tmtaa)(Htmtaa)·0.6CH₂Cl₂ (Ln = Sm 3, Tb 5, Er 6 and Yb 7) were determined by X-ray crystal diffraction. The complexes are isomorphous and the crystals belong to a monoclinic crystal system with the space group of C2/m. The rare earth(III) ions in the complexes are coordinated by eight nitrogen atoms from tmtaa and Htmtaa to form eight-coordinate sandwich complexes. The average Ln–N bond lengths for tmtaa and Htmtaa are 2.463(7) and 2.543(7) Å for 3, 2.438(7) and 2.540(7) Å for 5, 2.406(9) and 2.474(9) Å for 6 and 2.388(8) and 2.495(8) Å for 7, respectively. The tmtaa and Htmtaa in the complexes adopt markedly saddle conformations and coordinate to the rare earth(III) ions as delocalized conjugated π-electron systems. The acidic hydrogen in the complexes does not bind strongly to any of the nitrogen atoms of tmtaa or Htmtaa, but may belong to the four nitrogen atoms of Htmtaa. The influences of sandwich structures on the dihedral angles of the ligands were studied.