Diiron(III)‐Containing 23‐Tungsto‐2‐Borate: First Evidence of 3d Metal Substitution in the {BW 13 } Framework

The reaction of [HBW 11 O 39 ] 8– , (WO 4 ) 2– , and Fe 3+ (1:2:3 ratio) in water at pH 1.5 resulted in [{Fe III (H 2 O) 3 } 2 (WO 2 )(HBW 11 O 39 ) 2 ] 8– ( 1 ), the first 3d‐metal‐substituted tungstoborate whose structure differs from that of a monosubstituted Keggin framework. Polyanion 1 is composed of an unprecedented 23‐tungsto‐2‐borate subunit stabilized by Fe III coordination at the external positions. The linkage mode of the 11‐tungstoborate fragments in 1 evidences that substitution of tungsten by 3d metals can occur in the capping positions of the {BW 13 } skeleton.