Comparative analysis of the difference of local structure between EPR theory and X-ray diffraction experiment for NiSiF6·6H2O crystal

The local structure for NiSiF6·6H2O crystal has been investigated by diagonalizing the complete energy matrices. By simulating the EPR and optical spectra, the local structure parameter θ0 = 54.8901° is determined at room temperature and is different from θ′0=55.0899° obtained by X-ray diffraction experiment, suggesting that: (i) the H+ ions lead to a deviation of the equivalent position of effective charge of H2O molecule from O2− ion; (ii) the neighboring [SiF6]2− octahedral clusters lead to a deflection of the H2O molecules towards them. The deviation angle Δθ0 = −0.1998° is reported for the first time. Furthermore, the local structure of NiSiF6·6H2O crystal has been determined at 4.2 and 77 K.