Crystal structures of a tetranucleating macrocycle and its dimanganese(III) derivative, and magnetism of the latter

Abstract

Condensation of 2,6-bis(aminomethyl)-4-methylphenol with 2,6-diformyl-4-methylphenol gave a macrocyclic tetra-Schiff base containing two of each component as the dihydrochloride salt H₄L·2HCl, which has been studied by X-ray crystallography [triclinic, space group P(no. 2), a= 8.809(1), b= 9.268(2), c= 10.286(3)Å, α= 89.93(2), β= 84.70(2), γ= 72.18(2)°; at convergence R= 0.067 and R′= 0.060 for 982 reflections with l 2.5σ(I)]. The outstanding feature of the structure is that despite the overall dipositive charge resulting from protonation, the dialdehyde-derived oxygens are present as phenoxide anions. Crystals of composition [Mn₂(H₂L)(µ-O₂CMe)(µ-OH)(MeOH)₂][ClO₄]₂·2MeOH obtained from condensation of the dialdehyde and the diamine in the presence of Mn²⁺ and dioxygen were also studied by X-ray diffraction [monoclinic, space group C2/c(no. 15), a= 26.673(3), b= 11.069(3), c= 21.185(3)Å, β= 127.44(1)°; at convergence R= 0.061 and R′= 0.061 for 2102 reflections with I 3σ(I)]. The two equivalent manganese centres have tetragonally distorted six co-ordinate ligand environments consistent with the high-spin d⁴ configuration of the +III oxidation state, which is confirmed by the magnetic properties. The magnetic moment per Mn is 4.61 µ_B at room temperature falling to 1.8 µ_B at 10 K indicative of weak antiferromagnetic coupling with best-fit parameters obtained using a –2JS₁·S₂ Heisenberg model of g= 1.99(0.01), J=–4.0(0.1) cm^–1 and % monomer = 2.3(0.3).