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The experimental charge-density distribution of the dinuclear cobalt(II) complex [Co(2)(sym-hmp)(2)](BPh(4))(2)·2H(2)O·2C(3)H(6)O was determined at 100 K. When decreasing the temperature, the magnetic susceptibility of this complex deviates from Curie law because of anti-ferromagnetic exchange interactions, but the susceptibility increases sharply at low temperature (< 20 K). To explain this magnetic behaviour a tilt angle between the Co-atom environments was previously theoretically predicted. The structure and experimental charge density determined in this study show a tilt angle. The calculated value, based on the 100 K experimental d-orbital model, is in agreement with the theoretical one.

Magnetic properties of dinuclear nickel(II) complex [Ni(sym-hmp)](BPh)·3.5DMF·0.5(2-PrOH) (1), where (sym-hmp) is 2,6-bis[(2-hydroxyethyl)methylaminomethyl]-4-methylphenolate anion and DMF indicates dimethylformamide, were investigated using high-frequency and -field electron paramagnetic resonance (HFEPR). To magnetically characterize the mononuclear nickel(II) species forming the dimer, its two dinuclear zinc(II) analogues, [Zn(sym-hmp)](BPh)·3.5DMF·0.5(2-PrOH) (2) and [Zn(sym-hmp)](BPh)·2acetone·2HO (2'), were prepared. One of them (2') was structurally characterized by X-ray diffractometry and doped with 5% mol nickel(II) ions to prepare a mixed crystal 3. From the HFEPR results on complex 1 obtained at 40 K, the spin Hamiltonian parameters of the first excited spin state (S = 1) of the dimer were accurately determined as |D| = 9.99(2) cm, |E| = 1.62(1) cm, and g = [2.25(1), 2.19(2), 2.27(2)], and for the second excited spin state (S = 2) at 150 K estimated as |D| ≈ 3.5 cm. From these numbers, the single-ion zero-field splitting (ZFS) parameter of the Ni(II) ions forming the dimer was estimated as |D| ≈ 10-10.5 cm. The HFEPR spectra of 3 yielded directly the single-ion parameters for D = +10.1 cm, |E| = 3.1 cm, and g = 2.2. On the basis of the HFEPR results, the previously obtained magnetic data (Sakiyama, H.; Tone, K.; Yamasaki, M.; Mikuriya, M. Inorg. Chim. Acta 2011, 365, 183) were reanalyzed, and the isotropic interaction parameter between the Ni(II) ions was determined as J = -70 cm (H = -J S·S). Finally, density functional theory calculations yielded the J value of -90 cm in a qualitative agreement with the experiment.