EPR of Cr3+ in gallium acetylacetonate was studied at X-band. Two crystallographically inequivalent centers were observed. Their spin-Hamiltonian parameters (g = 1.997 (3); |6°| = 0.593 (3) and 0.599 (3) cm™1, respectively; |¿>|| = 0.03 (7) and 0.09 (7) cm™1, respectively) differ very little from each other and from those for the isomorphous aluminum and cobalt(III) compounds. No changes were observed between 298 and 20 K. Thus, the geometry of the paramagnetic ion in such molecular crystals seems to be little affected by changes in the size of the host ion and temperature. The zero-field-splitting (ZFS) pattern can be satisfactorily reproduced by the superposition model with an intrinsic ZFS parameter |62| of 5.0 cm™1. This pattern thus seems to be largely caused by the distortion of the first coordination sphere of oxygens. The cause of occurrence of two crystallographically inequivalent

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Zero field splitting (ZFS) parameters for [MnCl6]4‐ in three Cd compounds were determined and the validity of the superposition model was demonstrated by the consistent values of the intrinsic ZFS parameter b̄2 in all three cases as well as by a detailed comparison of the experimental ZFS pattern for one compound with that calculated from the crystal structure data. Additional ZFS data for [MnCl6]4‐ from the literature are also shown to lead to only slightly variable values of b̄2. – The change of the intrinsic ZFS parameter b̄2 from a negative value for F− to a larger positive value for Cl− as ligand is shown by detailed calculations for the various mechanisms to be due to the superponable overlap and covalency contributions as a result of increased charge transfer and ligand spin‐orbit coupling constant. The reliability of such calculations is still limited by the lack of experimental data for the transferred spin densities.

Trivalent ions of Fe, Cr and Mo are easily incorporated into CsCl‐type lattices. Evidently their geometries partly derive from those for divalent ions by exchange of a neutral molecule by hydroxyl or halide. In the ammonium halides hydrogen bonding manifests itself in predominance of low site symmetries and dynamic effects. Evidence for interstitial incorporation of di‐ and trivalent ions in quartz and isomorphous ABO4 compounds is also presented. EPR data for Fe3+ indicate simultaneous incorporation of O2− or OH− in the c‐axis channels. A kinetic reason for preferred interstitial incorporation is proposed. Enhanced mobilities of these as well as certain main constituents may also enhance the reactivities.