Fast degenerate double proton transfer in the solid state between two indazolinone tautomers

The neutral dimer formed by 4,6-difluoro-1H,2H-indazolin-3-one and 3-hydroxy-4,6-difluoro-1H-indazole linked by two hydrogen bonds presents a very fast intermolecular double proton transfer in the solid state (ISSPT). The combined use of crystallography, solid state NMR and DFT [B3LYP/6-311++G(d,p)] calculations supports this interesting observation and allows us to estimate a barrier of about 20 kJ mol-1. © 2010 The Royal Society of Chemistry.Peer Reviewe