Dinuclear nickel(II) complexes of a series of dinucleating macrocycles with similar or dissimilar coordination sites: synthesis, structure and physicochemical property

The dinucleating macrocycles H₂(L^m,n) containing two 2, 6-di(aminomethyl)-4-methylphenol entities combined through two alkane chains, -(CH₂)_m- (m=2, 3) and -(CH₂)_n- (n=2, 3, 4, 5), at the amine nitrogens, form nickel(II) complexes of the general formula [Ni₂(L^m,n)(OAc)₂] ((m, n)=(2,2), (2,4), (2,5), (3,3)) and [Ni₂(L^2,3)(OAc)(NCS)(CH₃OH)]. [Ni₂(L^2.2)(OAc)₂]·10H₂O crystallizes in the triclinic system of space group P1 with a=9.983(2), b=12.832(2), c=7.932(1) Å, α=101.29(1), β=101.08(2), γ=106.57(2)°, V=921.1(3) ų and Z=1. The refinement converges with R=5.65 and R_w=5.89% based on 2308 reflections with |F₀| > 3σ(|F₀|). The macrocycle adopts a folded conformation and each nickel has a cis-β octahedral geometry with the N₂O₂ donor set of the macrocycle and two oxygens of a bidentate acetate group. The Ni-Ni separation bridged by two phenolic oxygens is 3.004 Å and the Ni-O-Ni angle is 95.6°. Cryomagnetic properties (4.2-300 K) of the complexes are well reproduced based on the spin Hamiltonian H=-2JS₁·S₂-D(S_z1²-S_z2²) with a positive exchange integral (J=+10.1 to +2.1 cm^-1) and a negative zero-field splitting parameter (D=-0.53 to -2.40 cm^-1). Each complex shows two reduction waves and two oxidation waves attributable to the metal centers.