Bis(pentafluorophenyl)borinic Acid:  a Cyclic Trimer in the Solid State and a Monomer, with Hindered Rotation around the B−OH Bond, in Solution

The title molecule in the solid state exists as a cyclic trimer, with B−O(H)−B bridges and a cyclohexane-like structure (C 2 twist-boat conformation); dissolution in toluene-d 8 affords the B(C6F5)2OH monomer, in which the low-temperature 19F NMR data reveal restricted rotation of the OH substituent around the Ar2B−OH bond (E a = 39 kJ mol-1), as a result of the partial double-bond character of this interaction.