Mixed-ligand lanthanide complexes supported by ditopic bis(imino-methyl)-phenol/calix[4]arene macrocycles: synthesis, structures, and luminescence properties of [Ln2(L2)(MeOH)2] (Ln = La, Eu, Tb, Yb)

Ullmann, S.; Hahn, P.; Mini, P.; Tuck, K. L.; Kahnt, A.; Abel, B.; Gutierrez Suburu, M. E.; Strassert, C. A.; Kersting, B.

Research article (journal)

Abstract

The lanthanide binding ability of a macrocyclic ligand H6L2 comprising two bis(iminomethyl)phenol and two calix[4]arene units has been studied. H6L2 is a ditopic ligand which provides dinuclear neutral complexes of composition [Ln2(L2)(MeOH)2] (Ln = La (1){,} Eu (2){,} Tb (3){,} and Yb (4)) in very good yield. X-ray crystal structure analyses for 2 and 3 show that (L2)6− accommodates two seven coordinated lanthanide ions in a distorted monocapped trigonal prismatic/octahedral coordination environment. UV-vis spectroscopic titrations performed with La3+{,} Eu3+{,} Tb3+ and Yb3+ ions in mixed MeOH/CH2Cl2 solution (I = 0.01 M NBu4PF6) reveal that a 2 : 1 (metal : ligand) stoichiometry is present in solution{,} with log K11 and K21 values ranging from 5.25 to 6.64. The ratio α = K11/K21 of the stepwise formation constants for the mononuclear (L2 + M = ML2{,} log K11) and the dinuclear complexes (ML2 + M = M2L2{,} log K21) was found to be invariably smaller than unity indicating that the binding of the first Ln3+ ion augments the binding of the second Ln3+ ion. The present complexes are less luminescent than other seven-coordinated Eu and Tb complexes{,} which can be traced to vibrational relaxation of excited EuIII and TbIII states by the coligated MeOH and H2O molecules and/or low-lying ligand-to-metal charge-transfer (LMCT) states.

Details zur Publikation

Release year: 2020
Language in which the publication is written: English
Link to the full text: http://dx.doi.org/10.1039/D0DT02303E