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

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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.