Supramolecular Architectures from Ammonium-Crown Ether Inclusion Complexes in Polyoxometalate Association: Synthesis, Structure, and Spectroscopy

The tetrahedral (Td) molecular cation ammonium ion (NH4+) gets incorporated with the smaller-cavity crown ethers through three N+−H···O hydrogen bonding interactions, while the fourth N−H bond is projected outward from the crown ether cavity. A hydrogen bonding acceptor, such as a polyoxometalate anion, if placed in suitable position in the crystal lattice, can interact with the ammonium-crown ether supramolecular complex involving the fourth N−H bond donation. This article describes supramolecular association of ammonium-crown ether host−guest complexes with polyoxometalate anions in five crystalline solids, formulated as [NH4(B18C6)][Bu4N][Mo6O19] (1), [NH4(B18C6)]4[SiW12O40]·2CH3CN (2), [NH4(DB18C6)]2[Mo6O19]·4H2O (3), [NH4(DC18C6)]2[Mo6O19] (4), and [NH4(DB30C10)]2[Mo6O19]·CH3COOH (5), where B18C6 = benzo-18-crown-6, DB18C6 = dibenzo-18-crown-6, DC18C6 = dicyclohexyl-18-crown-6, and DB30C10 = dibenzo-30-crown-10. Single crystal X-ray structural investigations on these solids confer P1 space symmetry ...