A p-tert-butylcalix[6]arene bearing phosphinoyl pendant arms for the complexation and sensitisation of lanthanide ions

Abstract

The new lower rim functionalised macrocycle 5,11,17,23,29,35-hexa-tert-butyl-37,38,39,40,41,42-hexakis(dimethylphosphinoylmethoxy) (2) kJ mol Ϫ1 and reveal a semi-flexible macrocycle with alternate in-out cone conformation, a fact confirmed by molecular mechanics and dynamics calculations. B 6 bL 6 crystallises as a dimer where the two calixarenes are linked through hydrogen bonding and surrounded by water and toluene molecules in the lattice. UV-Vis spectrophotometric titration of B 6 bL 6 with La() in acetonitrile yields stability constants log β 1 = 9.8 and log β 2 = 19.6 for the 1 : 1 and 1 : 2 (Ln : B 6 bL 6 ) species, respectively. The corresponding complexes with La, Eu, Gd and Tb have been isolated and characterised. Lifetime determinations of the Eu() and Tb() complexes in acetonitrile solution are consistent with no or little interaction of water molecules in the inner co-ordination sphere. The new ligand sensitises reasonably well the luminescence of the Tb() (Q abs = 4.8%, τ f = 2.1 ms, 1 : 1 complex) and Eu() (Q abs = 2.5%, τ = 2.0 ms, 1 : 2 complex) ions.

Tuning the Stoichiometry of Lanthanide Complexes with Calixarenes: Bimetallic Complexes with a Calix[6]arene Bearing Ether‐Amide Pendant Arms

“…On the other hand, p-tert-butyl-substituted B 6 bL 6 displays a less labile alternate in-out conformation in which the six phosphanylyl pendant arms are located on the same side of the molecule, and no 2:1 complexes are obtained with this receptor but, instead, compounds with 1:1 and 1:2 stoichiometries can be isolated. [16] This demonstrates once again the versatility of the calixarene frameworks, since a conformation favoring a given stoichiometry of the Ln III complexes can be induced by modifying either the wider or the narrower rim of the ligand, a property which should prove useful in the development of convenient extraction systems.…”

“…Higher temperatures could not be reached, because the complex experiences de-metallation in DMSO, a solvent in which, for instance, B 6 bL 6 undergoes complete interconversion of its isomers on the NMR time scale at 132°C. [16] Photophysical Properties of A 6 under the same experimental conditions. [16] The absorption spectrum of the 2:1 complex in acetonitrile (4.74 ϫ 10 Ϫ5 ) displays three bands at 268 nm (37310 cm The lifetimes of the excited 5 D 0 level were measured at 10, 77, and 295 K both upon ligand and direct metal excitation ( Table 2).…”

“…[16] Photophysical Properties of A 6 under the same experimental conditions. [16] The absorption spectrum of the 2:1 complex in acetonitrile (4.74 ϫ 10 Ϫ5 ) displays three bands at 268 nm (37310 cm The lifetimes of the excited 5 D 0 level were measured at 10, 77, and 295 K both upon ligand and direct metal excitation ( Table 2). The luminescence decays of the solid state sample are bi-exponential and temperature dependent, decreasing roughly by a factor of two between 10 K and room temperature.…”

“…In addition, the crystal structure of the Lu III 1:1 complex shows the coordination cavity predisposed to further accommodate one water molecule hydrogen-bonded to the oxygen atoms of the phenol units, which rigidifies the induced cavity, and binds the metal ion. [14] The phosphanylyl-substituted calixarenes B n bL n (n ϭ 4, 6) form complexes with 1:1 and 1:2 Ln III ligand ratios having significant stability in acetonitrile, [15,16] and interesting luminescent [15,16] and 4fϪ5f separation [17] properties. Several derivatized calix [6]arenes have been tested in extraction studies [18Ϫ20] and, in our case, B 6 bL 6 proved to be a better extracting agent than B 4 bL 4 .…”

5f-Element complexes with a p-tert-butylcalix[4]arene bearing phosphinoyl pendant arms: Separation from rare earths and structural studies

“…Taking into account these considerations, we have been involved during the past years in the synthesis of two series of calix[n]arenes (n = 4, 6, 8, Scheme 1) fitted with ether amide [28,29] and phosphinoyl pendant arms on the narrow rim [11,[30][31][32]. We have reported the structural and photophysical properties of their lanthanide complexes [28][29][30][31][32].…”