Efficient synthesis of Ir-polyoxometalate cluster using a continuous flow apparatus and STM investigation of its coassembly behavior on HOPG surface

Taking advantage of a continuous-flow apparatus, the iridium(III)-containing polytungstate cluster K₁₂Na₂H₂[Ir₂Cl₈P₂W₂₀O₇₂]·37H₂O (1) was obtained in a reasonable yield (13% based on IrCl₃·H₂O). Compound 1 was characterized by Fourier transform IR, UV-visible, ³¹P NMR, electrospray ionization mass spectrometry (ESI-MS), and thermogravimetric analysis measurements. ³¹P NMR, ESI-MS, and elemental analysis all indicated 1 was a new polytungstate cluster compared with the reported K₁₄[(IrCl₄)KP₂W₂₀O₇₂] compound. Intriguingly, the successful isolation of 1 relied on the custom-built flow apparatus, demonstrating the uniqueness of continuous-flow chemistry to achieve crystalline materials. The catalytic properties of 1 were assessed by investigating the activity on catalyzing the electro-oxidation of ruthenium tris-2,2′-bipyridine [Ru(bpy)₃]^2+/3+. The voltammetric behavior suggested a coupled catalytic behavior between [Ru(bpy)₃]^3+/2+ and 1. Furthermore, on the highly oriented pyrolytic graphite surface, 1,3,5-tris(10-carboxydecyloxy) benzene (TCDB) was used as the two-dimensional host network to coassemble cluster 1; the surface morphology was observed by scanning tunneling microscope technique. "S"-shape of 1 was observed, indicating that the cluster could be accommodated in the cavity formed by two TCDB host molecules, leading to a TCDB/cluster binary structure.