Theoretical analysis of crystal field parameters and zero field splitting parameters for Mn2+ ions in tetramethylammonium tetrachlorozincate (TMATC-Zn)

Abstract

Superposition model (SPM) analysis is employed for modeling the crystal field parameters (CFPs) as well as the zero field splitting (ZFS) parameters (ZFSPs) for Mn2+ ions doped into tetramethylammonium tetrachlorozincate, [N(CH3)4]2ZnCl4 crystal (denoted TMATC-Zn). SPM analysis utilizes structural data to predict CFPs and ZFSPs determined for the dopant ions by optical and EMR spectroscopy, respectively. We report model calculations aimed at investigating the two structural options for dopant Mn2+ ions in TMATC-Zn: substitutional and interstitial sites. SPM is employed to predict CFPs, which serve as input for the perturbation theory expressions to calculate the 2nd-rank orthorhombic ZFSPs and to re-analyze optical spectra. Independently SPM is employed to predict the 2nd- and 4th-rank ZFSPs. Correlation of optical and EMR spectroscopy data increases modeling reliability. Comparison of the predicted 2nd-rank ZFSPs with the available experimental ones and consideration of the magnitudes of distortions required to achieve good matching enables discriminating between the substitutional and interstitial sites as location of doped Mn2+ ions. Our study indicates that interstitial sites are more plausible than substitutional sites for Mn2+ ions in TMATC-Zn, in agreement with the experimental prediction. The results reveal the importance of combining two separate methods to determine more reliably the most likely site for substitution of paramagnetic ions. This study also tests the range of applicability of CF theory and SPM analysis for Mn2+ ions in TMATC-Zn crystals and prepares grounds for consideration of the properties of molecular nanomagnets containing Mn2+ ions.