Formation Mechanism of a Nano‐Ring of Bismuth Cations and Mono‐Lacunary Keggin‐Type Phosphomolybdate

Abstract A new hetero‐bimetallic polyoxometalate (POM) nano‐ring was synthesized in a one‐pot procedure. The structure consists of tetrameric units containing four bismuth‐substituted monolacunary Keggin anions including distorted [BiO 8 ] cubes. The nano‐ring is formed via self‐assembly from metal precursors in aqueous acidic medium. The compound (NH 4 ) 16 [(BiPMo 11 O 39 ) 4 ] ⋅ 22 H 2 O; (P 4 Bi 4 Mo 44 ) was characterized by single‐crystal X‐ray diffraction, extended X‐ray absorption fine structure spectroscopy (EXAFS), Raman spectroscopy, matrix‐assisted laser desorption/ionisation‐time of flight mass spectrometry (MALDI‐TOF), and thermogravimetry/differential scanning calorimetry mass spectrometry (TG‐DSC‐MS). The formation of the nano‐ring in solution was studied by time‐resolved in situ small‐ and wide‐angle X‐ray scattering (SAXS/WAXS) and in situ EXAFS measurements at the Mo−K and the Bi−L 3 edge indicating a two‐step process consisting of condensation of Mo‐anions and formation of Bi−Mo‐units followed by a rapid self‐assembly to yield the final tetrameric ring structure.