STRUCTURAL AND MAGNETIC-PROPERTIES OF [NI-4(MU(3)-OME)(4)(DBM)(4)(MEOH)(4)] AND [NI-4(ETA(1)MU(3)-N-3)(4)(DBM)(4)(ETOH)(4)] - MAGNETOSTRUCTURAL CORRELATIONS FOR [NI(4)X(4)](4+) CUBANE COMPLEXES

Reaction of Ni(O(2)CMe)(2) . 4H(2)O with 1 molar equiv of Na(dbm) (dbmH = dibenzoylmethane) and NaOH in refluxing MeOH affords a green precipitate of [Ni-4(OMe)(4)(dbm)(4)(MeOH)(4)] (1), which can be recrystallized from chlorinated solvents; recrystallized yield 70%. Crystals of 1 . 2CH(2)Cl(2) have the following cell parameters at -111 degrees C: triclinic, P $($) over bar$$ 1, a = 14.566(2), b = 20.661(4), c = 13.367(2) Angstrom; alpha = 92.58(1), beta = 117.17(1), gamma = 72.87(1)degrees; V = 3433.2 Angstrom(3); Z = 2. The structure was solved and refined by employing 4631 reflections with F > 2.33 sigma(F) to final values of R (R(w)) of 6.00% (5.21%). The molecule consists of a [Ni-4(OMe)(4)](4+) cubane, each Ni-II ion being bound to three mu(3)-OMe(-) ions, one chelating dbm(-) group, and one terminal MeOH. Intramolecular hydrogen bonding between the MeOH and dbm(-) ligands leads to a distortion of the [Ni-4(OMe)(4)](4+) core from Td to D-2d 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) . 6H(2)O, NaN3, and Na(dbm) in EtOH at room temperature gives a green precipitate, which affords deep green crystals of [Ni-4-(N-3)(4)(dbm)(4)(EtOH)(4)] (3) in 78% yield upon recrystallization from chlorinated solvents; similar reactions in MeOH yield products in which MeO(-) has been partially substituted for N-3(-) Crystals of 3.2C(7)H(8) have the following cell parameters at -174 degrees C: monoclinic, P2(1)/n; a = 14.295(2), b = 23.203(4), c = 24.542(4) Angstrom; beta = 100.49(1)degrees; V = 8004.2 Angstrom(3); Z = 4. The structure was solved and refined by employing 6163 reflections with F > 2.33 sigma(F) to final values of R (R(w)) = 5.12% (4.44%). The molecule consists of a [Ni-4(N-3)(4)](4+) cubane, each Ni-II ion being bound to three (eta(1),mu(3)-N-3(-)) ligands, one chelating dbm(-) and one terminal EtOH. The disposition of ligands about the Ni-II ions and structural distortions caused by EtOH ... dbm(-) hydrogen bonding in 3 are identical to those of 1. The H-1 NMR, UV/visible, and (for 3) IR spectroscopic properties of 1 and 3 are consistent with octahedrally-coordinated Ni-II and strongly suggest that the [Ni-4(X)(4)(dbm)(4)(L)(4)] (X(-) = MeO(-), N-3(-); 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''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 J(1) = -3.4 cm(-1), J(2) = +12.2 cm(-1), g = 2.05, and O = +2.1 K (H = -2JS(1) . S-2). This is in agreement with the observed D-2d symmetry of the [Ni-4(OMe)(4)](4+) core in 1; a plot of J vs Ni-O-Ni bridging angle for 1 and other [Ni-4(OR)(4)](4+) cubanes shows an excellent linear correlation. By contrast, the variable-temperature magnetic behavior of 3 is well described by a one-J model in which all Ni Ni interactions are equivalent, with J = +11.9 cm(-1), g = 2.05, and Theta = +3.0 K, despite the observed D-2d Symmetry of the [Ni-4(N-3)(4)](4+) core. This result is in agreement with literature data for complexes bridged by a planar [Ni-2(eta(1),mu-N-3)(2)](2+) group, which show no obvious correlation between J and Ni-N-Ni angle.