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Investigating the Formation of Giant {Pd72}Prop and {Pd84}Gly Macrocycles Using NMR, HPLC, and Mass Spectrometry

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posted on 12.10.2018, 19:04 by Lorna G. Christie, Silke Asche, Jennifer S. Mathieson, Laia Vilà-Nadal, Leroy Cronin
The formation of giant polyoxo­metalate (POM) species is relatively under­explored, as their self-assembly process is complex due to the rapid kinetics. Polyoxo­palladates (POPds) are a class of POMs based on Pd, the largest of which is the {Pd84}Ac wheel, and its slower kinetics mean the system is more amenable to systematic study. Here, we show that it is possible to follow the assembly of two types of Pd wheels, {Pd84}Gly and the smaller {Pd72}Prop, formed using glycolate and propionate ligands, respectively. We analyzed the formation of {Pd72}Prop and {Pd84}Gly using mass spectrometry (SEC-HPLC-MS and preparative desalting followed by MS). This was accompanied by studies that followed the chemical shift differences between the outer/inner ligands and the free ligand in solution for the {Pd84}Ac, {Pd72}Prop, and {Pd84}Gly species using NMR, which showed it was possible to track the formation of the wheels. Our findings confirm that the macro­cycles assemble from smaller building blocks that react together to form the larger species over a period of days. These findings open the way for further structural derivatives and exploration of their host–guest chemistry.