A first report on ternary complex formation between p-sulfonatothiacalix[4]arene, tetramethylammonium ion and gadolinium (III) ion in aqueous solutions

Heterometallic CoIII–LnIII (Ln = Gd, Tb, Dy) Complexes on a p‐Sulfonatothiacalix[4]arene Platform Exhibiting Redox‐Switchable Metal‐to‐Metal Energy Transfer

“…Figure 1 shows the pH dependencies of R 1 in both binary Gd III -TCAS and ternary Gd III -TCAS-Co III systems. As it was stated in our previous work, [19] R 1 data first show the relaxivity decrease at pH 5-7, followed by an increase at pH 8-10 by implying the two-step binding of Gd III with TCAS. The first-step binding of TCAS (H 4 XNa 4 ) with Gd III is an equilibrium according to Equations (1) and (2), where complex [Gd(H 2 X)]…”

“…[10,11] It is worth noting that the inclusion of the complex becomes less for [Co(en) 2 The efficiency of NMR spectroscopic relaxation in the study of TCAS complex formation with Gd III ions in aqueous solutions was proved in our previous studies. [19] The high molar relaxivity (R 1 ) of Gd III enables NMR spectroscopic relaxation measurements to be performed in rather dilute Gd III -containing aqueous solutions (2.0 ϫ 10 -4 ). Figure 1 shows the pH dependencies of R 1 in both binary Gd III -TCAS and ternary Gd III -TCAS-Co III systems.…”

“…[19] The in-clusion of tetramethylammonium into the cavity of TCAS in the ternary Gd III -TCAS-TEMA system was found to favor the Gd III -TCAS first complexation step at pH 5-7 [Equation (2)], which is apparent from the shift in R 1 versus pH curve to more acidic media. This effect indicates that TEMA inclusion results in an enhancement in the complexability of the phenolate groups of the lower rim towards the gadolinium ion.…”

“…[17] The coordination of lanthanides through the sulfonate groups of TCAS is the predominant mode of binding in acidic media (pH 2-4), whereas at increased pH values (5-10) binding through the lower phenolate rim becomes more favorable. [18,19] It is interesting to note that TCAS with sulfur bridges exhibits more enhanced complexability towards lanthanide ions at pH 5-10 than its classic analogue (p-sulfonatocalix [4]arene) in aqueous solutions. [18] Moreover, the binding of the Tb III ion through the lower rim of TCAS results in rather intense luminescence due to the energy transfer from the triplet levels of TCAS to the emission level of Tb III .…”

“…The inclusion of an organic cation into the cavity along with metal-ion coordination by the hydroxy groups on the lower rim were estimated in both the solid state (from Xray data [20] ) and solutions. [19] It is worth noting that d metal complexes can be also bound by the upper rim of TCAS [11][12][13] and its classic analogue, [21,22] thus forming stable outer-sphere associates with calixarenes in both inclusive and noninclusive modes. The choice of Co III complexes as d blocks is conditioned by their chromophoric properties and kinetic inertness, as well as by our previous data.…”