Capture of the [Mo3S4]4+ Cluster within a {Mo18} Macrocycle Yielding a Supramolecular Assembly Stabilized by a Dynamic H-Bond Network

Abstract

The use of the [Mo(3)S(4)(Hnta)(3)](2-) complex (nta(3-) = nitrilotriacetate) as structuring agent toward the self-condensation process of the [Mo(2)O(2)S(2)(OH(2))(6)](2+) cation leads to the largest oxothiomolybdenum ring. In the solid state, X-ray diffraction analysis reveals the presence of the targeted molecular compound (noted 1a), which consists of the {Mo(18)O(18)S(18)(OH)(18)} host templated by the [Mo(3)S(4)(Hnta)(3)](2-) guest. Nevertheless, the structure shows an additional molecular moiety corresponding to a dinuclear unit {Mo(2)O(2)S(2)} coordinated to two nta(3-) ligands, mutually arranged in a cis fashion (1b). In the solid state, both entities interact through two short hydrogen bonds to give a striking supramolecular adduct, noted {1a-1b}. Synthetic procedures to prepare the individual species as pure compounds were reported. 1a was obtained as a pure mixed Cs(+)/NMe(4)(+) salt while the dinuclear unit [Mo(2)O(2)S(2)(Hnta)(2)](2-) was obtained as mixed K(+)/Na(+) crystals. X-ray diffraction study of the latter reveals a trans isomer (noted 1b'), characterized by the specific coordination of both nta(3-) ligands. All the compounds were characterized in solution (D(2)O or DMSO) by multiexperiment (1)H NMR (1D, COSY, NOESY, and DOSY). The overall results were consistent with the retention of the adduct {1a-1b} which exhibits a supramolecular reactivity. The dinuclear individual species in solution gave rise to cis-trans equilibrium, while in the presence of the oxothiomolybdenum ring 1a, the dinuclear unit is maintained as a frozen cis complex. DOSY NMR provides a definitive argument for the integrity of the supramolecular assembly. In addition, preliminary electrochemical study of 1a is also reported.