Effect of local structure on electron paramagnetic resonance spectra for trigonal Cr(H₂O)₆³⁺coordination complex in the sulfate alums series: a ligand field theory study

A simple theoretical method is introduced for studying the interrelation between electronic and molecular structures. By diagonalizing the 120×120 complete energy matrices, the relationships between zero-field splitting (ZFS) parameter D and local distortion parameter \Delta\theta for Cr³⁺ ions doped, separately, in \alpha- and \beta- alums are investigated. Our results indicate that there exists an approximately linear relationship between D and \Delta\theta in a temperature range 4.2--297 K and the signs of D and \Delta\theta are opposite to each other. Moreover, in order to understand the contribution of spin--orbit coupling coefficient \zeta to ZFS parameter D, the relation between D and \zeta is also discussed.