Direct Determination of the Single-Ion Anisotropy in a One-Dimensional Magnetic System by High-Field EPR Spectroscopy; Synthesis, EPR, and X-ray Structure of Ni x Zn1-x (C2O4)(dmiz)2 [x = 0.07]

The synthesis, X-ray structure, and EPR measurements of the integer-spin linear-chain antiferromagnet [Ni(ox)(dmiz)2] (where ox = C2O4 2- and dmiz = 1,2-dimethylimidazole) are presented. The sign and size of the single-ion zero field splitting (Zfs) of the divalent Ni have been determined by high field/high-frequency EPR spectroscopy. The spectra of powder samples of the derivatives [Ni x Zn1 - x (C2O4)(dmiz)2] for x = 0.09 and 0.07, at frequencies ranging from 110 to 440 GHz allowed the accurate determination of the zfs parameters D and E, with D = 1.875(4) cm-1 and E = 0.38 cm-1. The X-ray structure has been determined from measurements on a single crystal with x = 0.07. Structural parameters are as follows: a = 14.5252(7) Å, b = 12.1916(8) Å, c = 8.6850(8) Å, β = 97.460(6)° in space group C2/c. The zigzag chain contains octahedrally coordinated metal ions with two cis-oriented N-coordinated dmiz ligands and two cis-oriented, tetradentate bridging oxalato(2−) ligands, together resulting in a MN2O4 donor set. The structure was refined to a conventional R value of 0.073 for 1051 observed reflections. Zn−O distances are 2.167(5) Å and Zn−N = 2.098 Å. Coordination angles vary for cis angles from 78.4 to 100.7°, with trans angles varying from 163.9° to 165.5°.