Two nanosized polyoxothiometalates were synthesized based on linking oxomolybdate building blocks with {Mo2 O2 S2 }(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 {Mo9 O6 S3 }-type pores, which result in connections between {Mo6 O21 } pentagons and {Mo2 O2 S2 }(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 {Mo9 O6 S3 } 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.