Crystal Structure of Cs₄[{(C₆H₆)Ru}₂Nb₆O₁₉]·8MeOH·2H₂O. Structural Overview of Hybrid Organometallic Hexametalates of Niobium and Tantalum: Alkali Metal Coordination Behavior

Reaction of Cs₈[Nb₆O₁₉]·14H₂O with [(C₆H₆)RuCl₂]₂ leads to the formation of trans-[{(C₆H₆)Ru}₂Nb₆O₁₉]⁴⁻ (1). Evaporation of the reaction solution and extraction into methanol (MeOH) yielded Cs₄[{(C₆H₆)Ru}₂Nb₆O₁₉]·8MeOH·2H₂O (1a) as main product together with a small amount of Cs₄[{(C₆H₆)Ru}₂Nb₆O₁₉]·4MeOH·6H₂O (1b), both characterized by X-ray analysis. These structures complete a set of known organometallic polyoxoniobate or polyoxotantalate complexes [{Cp*M′}_xM₆O₁₉]ⁿ⁻ and [{(C₆H₆)Ru}_xM₆O₁₉]ⁿ⁻ (M = Nb, Ta; M′ = Rh, Ir; x = 1, 2; n = 6, 4; Cp* = η⁵-C₅(CH₃)₅) and give additional information about the importance of cation–anion interactions in the crystal structures of such complexes.