Optical Activity of Iron Group Selenate Crystals. I. Experimental Studies

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The absorption, circular dichroism (CD) and optical rotatory dispersion (ORD) of ZnSeO₄·6H₂O crystals, those doped with Cu²⁺, Ni²⁺ and Co²⁺ ions, and NiSeO₄·6H₂O crystals are measured in the 200–1500 mμ region at room temperature and 77 K. Several CD bands ascribed to the spin allowed d-d transitions are observed and the concomitant ORD curves are antisymmetric about the center of each CD band. The CD of NiSeO₄·6H₂O-ZnSeO₄·6H₂O mixed crystals depends linearly on the Ni²⁺ ion concentration, and the helical arrangement of metal ions is found not to be essential for the optical activity. It is concluded that the optical activity of these crystals is caused by the asymmetric field on the metal ions.