Abstract: | [Ho5(H2O)16(OH)2As6W64O220]25?, a Large Novel Polyoxoanion from Trivacant Keggin Fragments The novel polyoxotungstate Na7K18[Ho5(H2O)16(OH)2As6W64O220] · 56 H2O ( 1 ) was synthesized in aqueous solution and characterized by X‐ray structure analysis, elemental analysis and IR spectroscopy. The anion in 1 represents one of the largest polyoxoanions known yet and exhibits an unusual arrangement of six Keggin units. It consists of six trivacant lacunary α‐B‐(AsW9O33)9? Keggin fragments which are connected by a bridging [Ho5W10(H2O)16(OH)2O22]29+ unit. The five HoIII atoms are coordinated by eight oxygen atoms, forming a square‐antiprism. |