2009
DOI: 10.1002/chem.200902026
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A Simple Chemical Tuning of the Effective Concentration: Selection of Single‐, Double‐, and Triple‐Stranded Binuclear Lanthanide Helicates

Abstract: The replacement of terminal 2-benzimidazol-6-carboxypyridine (two internal rotational degrees of freedom) with 2-benzimidazol-8-hydroxyquinoline (one internal rotational degree of freedom) into segmental bis-tridentate ligands in going from L2 and [L3-2 H](2-) to [L12 b-2 H](2-) does not significantly affect the structures of the resulting binuclear lanthanide triple-stranded helical complexes [Ln(2)(L2)(3)](6+), [Ln(2)(L3-2 H)(3)], and [Ln(2)(L12 b-2 H)(3)] (palindromic helices, intermetallic contact distance… Show more

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Cited by 26 publications
(29 citation statements)
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“…For solubility reasons, the equilibrium shown in Equation (1) was monitored by 1 H NMR spectroscopy in [D 6 ]DMSO (Ln = La, Lu; k = 9, 11; Figure 1). In line with previous thermodynamic studies, [15] the concomitant formation of double-and triple-stranded helicates for Ln = Lu produces very complicated spectra ( Figure S2 in the Supporting Information), and we therefore focus on Ln = La, for which the larger stability constants ensure the exclusive formation of the triple-stranded helicate according to Equation (1) for a stoichiometric ratio La/Lk = 2:3 and a total ligand concentration of 5 mm (Figure 1). [15] Both diamagnetic [La 2 A C H T U N G T R E N N U N G (LkÀ2 H) 3 ] complexes (k = 9, 11) display seven signals for the aromatic protons (Hb-Hh in Figure 1), which are diagnostic for either D 3 (helical), C 3h (side-by-side = mesocate) or D 3h (nonhelical) point groups.…”
Section: Resultssupporting
confidence: 87%
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“…For solubility reasons, the equilibrium shown in Equation (1) was monitored by 1 H NMR spectroscopy in [D 6 ]DMSO (Ln = La, Lu; k = 9, 11; Figure 1). In line with previous thermodynamic studies, [15] the concomitant formation of double-and triple-stranded helicates for Ln = Lu produces very complicated spectra ( Figure S2 in the Supporting Information), and we therefore focus on Ln = La, for which the larger stability constants ensure the exclusive formation of the triple-stranded helicate according to Equation (1) for a stoichiometric ratio La/Lk = 2:3 and a total ligand concentration of 5 mm (Figure 1). [15] Both diamagnetic [La 2 A C H T U N G T R E N N U N G (LkÀ2 H) 3 ] complexes (k = 9, 11) display seven signals for the aromatic protons (Hb-Hh in Figure 1), which are diagnostic for either D 3 (helical), C 3h (side-by-side = mesocate) or D 3h (nonhelical) point groups.…”
Section: Resultssupporting
confidence: 87%
“…[14,16] The final thiol-ene clickcoupling radical reactions provided L12 Cn (n = 3, 12) in good yields. [17] As previously established for L9, [15] the mixing of the more constrained ligand L11 (3 equiv) with LnA C H T U N G T R E N N U N G (OTf) 3 ·x H 2 O (2 equiv; Ln = La, Lu; OTf À = CF 3 SO 3 À = triflate; x = 1-3) in aprotic solvent (CH 3 CN or DMSO) containing nBu 4 NOH (6 equiv) also yields orange solutions. ESI-MS spectra of the crude reaction solutions reveal weak signals corresponding to the formation of a small amount of protonated triple-heli-…”
Section: Resultsmentioning
confidence: 96%
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