Optical phonons in α‐NiSO 4 ·6H 2 O single crystal

Laser excited Raman spectra of a single crystal of α‐NiSO 4 ·6H 2 O have been attributed to the phonons originating only from the Raman active modes of isolated H 2 O ( C 2 v ), SO   4 2−( T d ) and Ni(H 2 O)   6 2+( O h ) units. It has been shown that T h symmetry considered earlier for NI(H 2 O)   6 2+complex by Jager and Schaack is not consistent with the crystal structure of α‐NiSO 4 ·6H 2 O and results in an erroneous symmetry classification of 288 phonon branches of the unit cell. A correct classification of these branches is reported. It is inferred that the SO   4 2−and Ni(H 2 O)   6 2+polyhedra do not show large distortions from their respective T d and O h symmetries at room temperature.