Tunable Keplerate Type‐Cluster “Mo₁₃₂” Cavity with Dicarboxylate Anions

Abstract

The internal functionalization of the Keplerate-type capsule Mo132 has been carried out by ligand exchange leading to the formation of glutarate and succinate containing species isolated as ammonium or dimethylammonium salts. Solution NMR analysis is consistent with asymmetric inner dicarboxylate ions containing one carboxylato group grafted onto the inner side of the spheroidal inorganic shell while the second hangs toward the center of the cavity. Such a disposition has been confirmed by the single-crystal X-ray diffraction analysis of the glutarate containing {Mo132 } species. A detailed NMR solution study of the ligand-exchange process allowed determining the binding constant KL of acetate (AcO(-) ), succinate (HSucc(-) ) or glutarate (HGlu(-) ) ligands at the 30 inner coordinating sites, which vary such as K AcO -<K HGlu -<K HSucc --supported by the associated thermodynamic parameters Δr S* and Δr H*. Such a variation is mainly explained by a positive entropic gain attenuated by unfavorable steric effect. Furthermore, these results are completed by (1) H DOSY and (1) H EXSY NMR experiments which are in agreement with bulky guests firmly trapped within the cavity. At last, variable temperature (1) H NMR study below 290 K revealed a striking line broadening occurring abruptly within a 5 K range. Such an effect appears closely related to the presence of the ammonium cations suspected to be present within the cavity and then has been interpreted as an inner-phase transition leading to a frozen state.

Densely Packed Hydrophobic Clustering: Encapsulated Valerates Form a High‐Temperature‐Stable {Mo132} Capsule System

“…The final refinement was done accordingly with 24 coordinated valerate ligands (C atoms of the carboxylate group have an 80 % occupancy). A similar composition has been quite recently reported for a glutamate‐type capsule …”

Designing Functional Polyoxometalate‐Based Ionic Liquid Crystals and Ionic Liquids

“…The Linqvist structure [M 6 O 19 ] xand its derivatives (Figure 1) are probably the main archetypical structure of this class but in the domain of isopolyoxomolybdates, Müller et al opened a new field of investigation when they reported the discovery of a fullerene-like, all-inorganic hollow spheres containing 132 molybdenum centers in 1998 (Figure 1). [30] [21,[31][32][33] Not only aesthetic, these nanometric hollow clusters behave as functional nanoflasks for cations or molecules trapping, [34][35][36][37] catalysis [38] or specific chemical transformations. [39] This family of polyoxomolybdates was also complemented by other giant POMs namely the "big wheels" {Mo-154}, {Mo-176} and {Mo-248}, and the "blue lemon" {Mo-368}, which expanded the frontiers of inorganic chemistry to the mesoscopic world (see Figure 1).…”

Electronic Structure Studies on the Whole Keplerate Family: Predicting New Members

“…These ligands are usually bidentate oxygen donor anions, such as formate, [5] acetate, [2b] monochloroacetate, [5c] sulfate, [2b, 6] sulfite, [7] hypophosphite, [8] hydrogen phosphate, [9] selenate, [10] valerate, [11] carbonate, [8] carboxylates in general, [12] or even dicarboxylates. [13] Thesel igands are labilely bonded to the inner surface of the capsule. Therefore, they are able to exchange their positions insideo ft he Keplerate or even with solvated anionsf rom the outer medium through the pores.…”

“…In the general formula of Keplerates, L represents a bidentate ligand that can be coordinated to the inner surface of the capsule. These ligands are usually bidentate oxygen donor anions, such as formate, acetate, monochloroacetate, sulfate, sulfite, hypophosphite, hydrogen phosphate, selenate, valerate, carbonate, carboxylates in general, or even dicarboxylates . These ligands are labilely bonded to the inner surface of the capsule.…”