Janus Cluster: Asymmetric Coverage of a Ag43 Cluster on the Symmetric Preyssler P5W30 Polyoxometalate

An anion template generally exerts an inductive effect by forming a fully covered outer shell around it; however, partial coverage to form an entity with either an anisotropic structure or a regioselective distribution of functional groups, called the Janus cluster, is still challenging. An attempt at creating asymmetric core–shell hybrid structures using the high-symmetry Preyssler polyoxometalate (POM) as anion template and [Ag(tBuC≡C)]n to generate the shell resulted in {[K(H2O)HP5W30O110]@Ag43(tBuC≡C)29(CN)(CH3CN)(H2O)}·4CH3CN (SD/Ag43a) with only ca. 60% surface coverage. The asymmetric Ag43 shell comprises two segments, Ag16(tBuC≡C)10 and Ag25(tBuC≡C)15, linked by a pair of Ag(tBuC≡C)2 units. This is an unprecedented example of an asymmetrical coverage on a symmetrical Preyssler P5W30. Electrospray ionization mass spectrometry (ESI-MS) indicates the progressive addition of [Ag(tBuC≡C)] to the surface in forming SD/Ag43a. Due to the incomplete Ag shell on the P5W30 core, both components have exposed surfaces, resulting in typical redox peaks from both P5W30 and the Ag(I) cluster being clearly detected in cyclic voltammetry, which demonstrates the successful dual functionalization of the POM and silver cluster hybrid.