Structural and Magnetic Properties of [Ni4(μ3-OMe)4(dbm)4(MeOH)4] and [Ni4(η1,μ3-N3)4(dbm)4(EtOH)4]. Magnetostructural Correlations for [Ni4X4](4+) Cubane Complexes

Article abstract of DOI:10.1021/ic00120a022

Reaction of Ni(O2CMe)2.4H2O with 1 molar equiv of Na(dbm) (dbmH = dibenzoylmethane) and NaOH in refluxing MeOH affords a green precipitate of [Ni4(OMe)4(dbm)4(MeOH)4] (1), which can be recrystallized from chlorinated solvents; recrystallized yield 70%. Crystals of 1.2CH2Cl2 have the following cell parameters at -111°C: triclinic, P1-, a = 14.566(2), b = 20.661(4), c = 13.367(2) ?; α = 92.58(1), β = 117.17(1), γ = 72.87(1)°; V = 3433.2 ?**3; Z = 2. The structure was solved and refined by employing 4631 retlections with F > 2.33σ(F) to final values of R (Rw) of 6.00% (5.21%). The molecule consistsof a [Ni4(OMe)4](4+) cubane, each Ni(II) ion being bound to three μ3-OMe(1-) ions, one chelating dbm(1-) group, and one terminal MeOH. Intramolecular hydrogen bonding between the MeOH and dbm(1-) ligands leads toa distortion of the [Ni4(OMe)4](4+) core from Td to D2d symmetry, resulting in two types of Ni2O2 faces within the cubane structure with differing Ni..Ni distances, Ni-O-Ni angles, and Ni-O-O-Ni dihedral angles. Reaction of a 1:1:1 molar ratio of Ni(ClO4)2.6H2O, NaN3, and Na(dbm) in EtOH at room temperature gives a green precipitate, which affords deep green crystals of [Ni4(N3)4(dbm)4(EtOH)4] (3) in 78% yield upon recrystallization from chlorinated solvents; similar reactions in MeOH yield products in which MeO(1-) has been partially substituted for N3(1-). Crystals of 3.2C7H8 have the following cell parameters at -174°C: monoclinic, P21/n; a = 14.295(2), b = 23.203(4), c = 24.542(4) ?; β = 100.49(1)°; V = 8004.2 ?**3; Z = 4. The structure was solved and refined by employing 6163 reflections with F > 2.33σ(F) to finalvalues of R (Rw) = 5.12% (4.44%). The molecule consists of a [Ni4(N3)4](4+) cubane, each Ni(II) ion being bound to three (η1,μ3-N3(1-)) ligands, one chelating dbm(1-) and one terminal EtOH. The disposition ofligands about the Ni(II) ions and structural distortions caused by EtOH...dbm(1-) hydrogen bonding in 3 are identical to those of 1. The (1)H NMR, UV/visible, and (for 3) IR spectroscopic properties of 1 and 3 are consistent with octahedrally-coordinated Ni(II) and strongly suggest thatthe [Ni4(X)4(dbm)4(L)4] (X(1-) = MeO(1-), N3(1-); L = alcohol, solvent)structure is retained in chlorinated solvents. Both 1 and 3 show only irreversible processes by cyclic voltammetry in CH2Cl2/0.5 M Bu(n)4NClO4 at 293 K. The solid-state variable-temperature effective magnetic moment(5.00-320 K) of 1 is modeled by a two-J equation giving J1 = -3.4 cm**-1, J2 = +12.2 cm**-1, g = 2.05, and Θ = +2.1 K (H = -2JS1.S2). This is in agreement with the observed D2d symmetry of the ...