Macrocyclic tetranuclear manganese(II) complexes of a new ‘dimer of dimers’ type: synthesis, structure and magnetism

Abstract

The template reaction of 2,6-diformyl-4-methylphenol, 1,8-diamino-3,6-dialkyl-3,6-diazaoctane (alkyl = methyl or ethyl) and manganese(II) benzoate tetrahydrate in 1:1:2 molar ratio leads to the formation of a macrocyclic tetranuclear manganese(II) complex [Mn₄(Lⁿ)(PhCO₂)₆] where H₂Lⁿ is a [2 + 2] macrocycle obtained by condensation of 2,6-diformyl-4-methylphenol and 1,8-diamino-3,6-dialkyl-3,6-diazaoctane [alkyl = methyl (L²) or ethyl (L³)]. An adduct of the L² complex. [Mn₄L²(PhCO₂)₆-(Me₂CHOH)₂]·2CH₂Cl₂, crystallizes in the orthorhombic space group Pbca with a= 20.692(3), b= 20.074(3), c= 22.988(5)Å and Z= 4. The refinement converged to R= 0.0899 and R′= 0.0942 based on 3798 reflections with |F₀| > 3σ(|F₀|). The complex molecule is centrosymmetric and contains two pairs of manganese ions bridged by a phenolic oxygen of L² and two benzoate groups. The manganese ions in each pair are inequivalent. One is bound to the phenolic oxygen, one imino nitrogen and two amino nitrogens of L² and assumes a six-co-ordinate geometry co-ordinating to two oxygens of the bridging benzoate groups. The other is bound to the bridging phenolic oxygen and an imino nitrogen of L², two bridging benzoate oxygens, one monodentate benzoate oxygen, and one propan-2-ol oxygen to assume a six-co-ordinate geometry. Magnetic susceptibility measurements over the temperature range of 4.2-300 K indicate a weak antiferromagnetic interaction between the manganese(II) ions in each pair (J≈–4 cm^–1 based on Ĥ=–2JS₁·S₂) and no magnetic interaction between the two pairs.