Breaking symmetry: Spontaneous resolution of a polyoxometalate

A chiral polyoxometalate [Hf(PW11O39)(2)](10-) (1) has been prepared and structurally characterized. It crystallizes in the chiral space group P2(1)2(i)2, as a conglomerate of two enantiomerically pure crystals in the absence of any chiral source. The absolute configuration of 1 was determined from the Flack parameter by X-ray crystallography. The structure of 1 comprises two lacunary [PW11O39](7-) units, each functioning as a tetra-dentate ligand sandwiching an 8-coordinate Hf-IV centre in a distorted square antiprismatic geometry. Optically active crystals of both enantionters were spectroscopically distinguishable by means of solid state circular dichroism spectroscopy. This hafnium-substituted polyoxometalate (POM), 1, shows that spontaneous chiral resolution, a rare phenomenon, can be operable in POM systems.