Tracking “Apolar” NMe₄⁺ Ions within Two Polyoxothiomolybdates that Have the Same Pores: Smaller Clathrate and Larger Highly Porous Clusters in Action

Abstract

Two nanosized polyoxothiometalates were synthesized based on linking oxomolybdate building blocks with {Mo2O2S2}(2+) groups. Remarkably, both compounds are formed selectively primarily upon changing the related concentrations in a logical way; they exhibit common structural features based on the same {Mo9O6S3}-type pores, which result in connections between {Mo6O21} pentagons and {Mo2O2S2}(2+) linkers. Whereas the much larger spherical Mo132-type Keplerate contains twenty pores, the smaller Mo63 -type cluster remarkably contains only two. The two compounds and a similar Keplerate exhibit interesting supramolecular properties related to interactions with the unusual predominantly apolar NMe4(+) cations. Structural characterization of the Mo63 -type compound reveals in the solid state a clathrate-like species that contains four NMe4(+) cations embedded in two types of structurally well-adapted pockets. Related NMR spectroscopic investigations in solution using NMe4(+) as the NMR spectroscopic probe are in agreement with the solid-state description. (1)H NMR spectroscopic experiments (1D variable-temperature, 2D total correlation spectroscopy (TOCSY), exchange spectroscopy (EXSY), and diffusion-ordered spectroscopy (DOSY)) feature firmly immobilized and mobile NMe4(+) ions in relationship with the type of host-guest arrangements. The use of the (1)H NMR DOSY spectroscopic methodology has been successfully applied to track the interactions of the NMe4(+) cations with the {Mo9O6S3} pores of a sulfurated Keplerate, thereby allowing the first quantitative analysis of this type of plugging process. The stability constant K=(210±20) mol(-1) L is discussed related to the character of the process.

Hydrophobic Effect as a Driving Force for Host–Guest Chemistry of a Multi-Receptor Keplerate-Type Capsule

“…Changing the nature of the pore from {Mo 9 O 9 } to {Mo 9 S 3 O 6 } leads to a drastic decrease of the stability constant from K S = 1550 ± 200 to 210 ± 20 while the main features of the capsule (ionic charge, size and shape) remain almost unchanged. 19 The rationale of such a result is the larger ionic radius of the sulfur atom which reduced the inner space of the pore and then increases the unfavorable steric effect for the NMe 4 + plugging. We tried to get Xray diffraction structural data to support these solution studies.…”

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

“…Such an observation has been fully analyzed from an experimental and theoretical point of views in a recent report which demonstrates that specific interactions between the capsules and DMA + cations take place involving the twenty {Mo 6 O 9 } ether crown‐like pores of the capsule 30. Such specific interactions have been observed also in solution between the NMe 4 + ion and the sulfurated Keplerate [Mo 132 O 312 S 60 (H 2 O) 72 (CH 3 COO) 30 ] 42− 31. Such solution studies and related results correspond to complementary insights previously evidenced in the solid state and described as the pore plugging process 32…”

Designing Functional Polyoxometalate‐Based Ionic Liquid Crystals and Ionic Liquids

“…[83] In this case, the alkyl chain length is probably too small to get liquid crystals phase but they used it to prepare coassembly of spherical 6.2 nm maghemite (- ligands and higher charge. [33] The larger charge of the capsule allows associating more [82,84] with the permission from the Royal Society of Chemistry) 33represents an attractive system. [85] It possesses a large anionic pocket of about 1 nm in diameter, which is able to include various transition metals, a key step for the elaboration of efficient materials for magnetic, luminescent, catalytic or electrocatalytic properties.…”

“…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).…”