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Scientific article
English

In search for tuneable intramolecular intermetallic interactions in polynuclear lanthanide complexes

Published inDalton transactions, no. 37, p. 7625-7638
Publication date2009
Abstract

Reaction of unsymmetrical tridentate 2-benzimidazolyl-6-carboxamidopyridine binding units in the ligands (b) and with neutral Ln(NO(3))(3) (Ln is a trivalent lanthanide) gives mononuclear [Ln((b))(NO(3))(3)(solvent)] and binuclear [Ln(2)(L5)(NO(3) (6)(solvent)(2)] complexes. The crystal structures of (b) and [Eu((b))(NO(3))(3)(CH(3)CN)] unravel the conformational change of the tridentate binding units required for its coordination to the metal, a process responsible for the change in electronic absorption spectra and in (1)H NMR spectra recorded in acetonitrile solution. In the solid state, the bis-tridentate ligand shows variable helical conformations of its central diphenylmethane spacer in its uncoordinated form (amphiverse helix) and in its complexed form in [Eu(2)(L5)(NO(3))(6)(H(2)O)(2)] (regular helix), which puts the two metals at a contact distance of 8.564(1) A. In solution, fast rearrangements yield an average planar extended conformation of the spacer, which increases the intramolecular intermetallic contact distance by 30% in [Ln(2)(L5)(NO(3))(6)(H(2)O)(2)]. Surprisingly, the thermodynamic analysis of the complexation processes in solution points to unusual, and to some extent non-predicted charge effects because the intramolecular intermetallic repulsive interaction measured in the neutral complex [Ln(2)(L5)(NO(3))(6)] (Ln...Ln approximately 12 A) is comparable with that found in the highly charged triple-stranded helicate [Ln(2)(L5)(3)](6+) (Ln...Ln approximately 9 A). The origin of this effect and its consequences on programming stable polynuclear complexes is discussed.

Citation (ISO format)
DALLA FAVERA, Natalia et al. In search for tuneable intramolecular intermetallic interactions in polynuclear lanthanide complexes. In: Dalton transactions, 2009, n° 37, p. 7625–7638. doi: 10.1039/b905131g
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ISSN of the journal1477-9226
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