Strong Cluster-Supported Brønsted Acids: Hexanuclear Niobium Cluster Compounds with Protonated Crown Ether Cations: (Crown-H) 2 [Nb 6 Cl 12 i X 6 a ] (X = Cl or Br) and the Intermediate [Nb 6 Cl 16 (H 2 O) 2 ]·4 dioxane.

Six cluster salts which consist of hexanuclear cluster anions [Nb 6 Cl 12 i X 6 a ] 2- ( X = Cl or Br) and protonated crown ether molecules (15-crown-5 (15cr5) and 12-crown-4 (12cr4)) or crown ether-stabilized oxonium cations as well as one compound consisting of neutral cluster units, [Nb 6 Cl 16 (H 2 O) 2 ]·4 dioxane, were synthesized in good to high yields. The single-crystal X-ray structures of six of these compounds were determined. The cation/anion ratios and the bond distances confirm in all cases oxidized cluster cores with 14 cluster-based electrons. The cations of the cluster salts are either sandwich-type dimers of the formula [(15cr5)H] 2 2+ or [(15cr5)(H 3 O)] 2 2+ with the protons or oxonium ions embedded in between the crown ether rings or monomeric units in the case of [(12cr4)H] + . 1 H NMR investigations show that the cluster salts are strong Brønsted acids. The fact that the cluster core of [Nb 6 Cl 16 (H 2 O) 2 ]·4 dioxane is oxidized but still carries water ligands indicates that within the multi-step reaction sequence of the formation of the cluster-supported acids, the oxidation step happens much faster than the ligand exchange steps. Temperature-dependent 2 H MAS NMR spectra of deuterium-exchanged [(15cr5)H] 2 [Nb 6 Cl 18 ]·2 CHCl 3 are indicative of dynamic processes of the hydrogen-bonded protons within the crown ether molecule.