Magnetic Properties of a Dinuclear Nickel(II) Complex with 2,6-Bis[(2-hydroxyethyl)methylaminomethyl]-4-methylphenolate

Magnetic properties of dinuclear nickel­(II) complex [Ni₂(sym-hmp)₂]­(BPh₄)₂·3.5DMF·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, [Zn₂(sym-hmp)₂]­(BPh₄)₂·3.5DMF·0.5­(2-PrOH) (2) and [Zn₂(sym-hmp)₂]­(BPh₄)₂·2acetone·2H₂O (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 |D₁| = 9.99(2) cm^–1, |E₁| = 1.62(1) cm^–1, and g₁ = [2.25(1), 2.19(2), 2.27(2)], and for the second excited spin state (S = 2) at 150 K estimated as |D₂| ≈ 3.5 cm^–1. From these numbers, the single-ion zero-field splitting (ZFS) parameter of the Ni­(II) ions forming the dimer was estimated as |D_Ni| ≈ 10–10.5 cm^–1. The HFEPR spectra of 3 yielded directly the single-ion parameters for D_Ni = +10.1 cm^–1, |E_Ni| = 3.1 cm^–1, and g_iso = 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^–1 (H_ex = −J S_A·S_B). Finally, density functional theory calculations yielded the J value of −90 cm^–1 in a qualitative agreement with the experiment.