Crystal Growth, Structure, and Noninteracting Quantum Spins in Cyanochroite, K 2 Cu(SO 4 ) 2 ·6H 2 O.

The rare mineral cyanochroite, K 2 Cu(SO 4 ) 2 ·6H 2 O, features isolated Cu 2+ ions in distorted octahedral coordination, linked via a hydrogen-bond network. We have grown single crystals of cyanochroite as large as ∼0.5 cm 3 and investigated structural and magnetic aspects of this material. The positions of hydrogen atoms deviate significantly from those reported previously based on X-ray diffraction data, whereas the magnetic response is fully consistent with free Cu 2+ spins. The structure is not changed by deuteration. Density functional theory calculations support our refined hydrogen positions.