Strong Cluster-Supported BrÃ¸nsted Acids: Hexanuclear Niobium Cluster Compounds with Protonated Crown Ether Cations: (Crown-H)2[NCl12ia] (X = Cl or Br) and the Intermediate [NCl16(O)2]Â·4 dioxane
J. Koenig, T. Gutmann, G. Buntkowsky, M. Koeckerling, Inorganic Chemistry 61 (2022) 15983–15990.