Crystallographic Studies of a Molybdenum‐Rich Diarsenotungstate and Reaction of Fe III with Its Isomerically Pureα 1 ‐ and α 2 ‐Monolacunary Derivatives

An isomerically pure form of the molybdenum‐richpolytungstate, [α 1 ‐As 2 Mo 5 W 12 O 61 ] 10– , was prepared by adding 5 equivalents of Mo VI to [α‐H 2 As 2 W 12 O 48 ] 12– , in thepresence of Li + . The α 2 ‐isomer, [α 2 ‐As 2 Mo 5 W 12 O 61 ] 10– , was prepared by mild alkaline (KHCO 3 ) degradation of[α‐As 2 Mo 6 W 12 O 62 ] 6– . Both [α 1 ‐As 2 Mo 5 W 12 O 61 ] 10– and [α 2 ‐As 2 Mo 5 W 12 O 61 ] 10– react with Fe III in aqueous solution to give [α 1 ‐As 2 (FeOH 2 )Mo 5 W 12 O 61 ] 7– ( 1 ) and [α 2 ‐As 2 (FeOH 2 )Mo 5 W 12 O 61 ] 7– ( 2 ), respectively. The parent complex, [α‐As 2 Mo 6 W 12 O 62 ] 6– , was characterized by X‐ray crystallography as a mixed potassium‐sodium salt [ a = 12.8412(17) Å, b = 14.8145(19) Å, c = 19.913(3) Å, α = 70.058°, β = 81.055(5)°, γ = 64,495°, triclinic, P $\tilde {1}$ , R 1 = 4.99 % based on 9709 reflections]. All of the complexes were characterized by infrared spectroscopy, cyclic voltammetry, and elemental analyses. 183 W NMR studies confirm that 1 and 2 are isomerically pure compounds. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)