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). Issue 32 (4th August 2020)

• Record Type: Journal Article
• Authors: Ullmann, Steve; Hahn, Peter; Mini, Parvathy; Tuck, Kellie L.; Kahnt, Axel; Abel, Bernd; Gutierrez Suburu, Matias E.; Strassert, Cristian A.; Kersting, Berthold
• Is Part Of: Dalton transactions. Volume 49:Issue 32(2020)
• Page Start: 11179
• Page End: 11191
• Publication Date: 2020-08-04
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/d0dt02303e
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : H6 L 2 was found to be an effective dinucleating ligand for various Ln 3+ ions forming luminescent, mixed-ligand complexes of composition [Ln2 (L 2 )(MeOH)2 ] with one exchangeable coligand per seven-coordinated Ln site. Abstract : The lanthanide binding ability of a macrocyclic ligand H6 L 2 comprising two bis(iminomethyl)phenol and two calix[4]arene units has been studied. H6 L 2 is a ditopic ligand which provides dinuclear neutral complexes of composition [Ln2 (L 2 )(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 (L 2 ) 6− accommodates two seven coordinated lanthanide ions in a distorted monocapped trigonal prismatic/octahedral coordination environment. UV-vis spectroscopic titrations performed with La 3+, Eu 3+, Tb 3+ and Yb 3+ ions in mixed MeOH/CH2 Cl2 solution ( I = 0.01 M NBu4 PF6 ) reveal that a 2 : 1 (metal : ligand) stoichiometry is present in solution, with log K 11 and K 21 values ranging from 5.25 to 6.64. The ratio α = K 11 / K 21 of the stepwise formation constants for the mononuclear (L 2 + M = ML 2, log K 11 ) and the dinuclear complexes (ML 2 + M = M2 L 2, log K 21 ) was found to be invariably smaller than unity indicating that the binding of the first Ln 3+ ion augments the binding of the second Ln 3+ ion. The present complexes are less luminescent than other seven-coordinated Eu and Tb complexes, which can be traced to vibrational relaxation of excited Eu III and Tb III states by the coligated MeOH and H2 O molecules and/or low-lying ligand-to-metal charge-transfer (LMCT) states.