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Polynuclear manganese(II) complexes with Robson-type ligands. Synthesis, characterization, molecular structure, and magnetic properties

1988; Royal Society of Chemistry; Issue: 5 Linguagem: Inglês

10.1039/dt9880001225

2050-5671

Dominique Luneau, Jean‐Michel Savariault, P. Cassoux, Jean‐Pierre Tuchagues,

Metal-Catalyzed Oxygenation Mechanisms

The synthesis, infrared and e.s.r. spectra, and variable-temperature magnetic susceptibility of seven manganese(II) complexes with macrocyclic Robson-type ligands and chloride, bromide, or acetate and perchlorate anions are described. The ligands include a symmetric macrocycle (L1) resulting from the condensation of 2,6-diformyl-4-methylphenol with 1,3-diaminopropane and asymmetric macrocycles resulting from the two-step condensation of 2,6-diformyl-4-methylphenol with 1,3-diaminopropane and 1,3-diamino-2-hydroxypropane (L2). The crystal molecular structure of [Mn2L2(MeCO2)]ClO4 has been established by X-ray diffraction methods. This complex crystallizes in the triclinic system, space group P, in a cell of dimensions a= 12.513(8), b= 13.67(1), c= 8.699(8)Å, with Z= 2. The structure was solved by the direct method and refined by a succession of difference Fourier syntheses and least-squares refinements. An unresolved disorder of the perchlorate anion has set the agreement indices of the structure to R= 0.114 and R′= 0.142 for 2 968 reflections. X-Ray powder patterns and a large angle X-ray scattering study allowed us to determine the main structural features of the six remaining complexes. Minor changes, either in the macrocyclic ligand or in the nature of the anions, result in different molecular structures and magnetic behaviour of the complexes. The complexes [Mn2L1Cl2], [Mn2L2Cl2], [Mn2L1Br2], and [Mn2L2Br2] are built from isolated binuclear units with an axially-distorted square-pyramidal geometry around each manganese ion. The manganese ion is displaced out of the macrocyclic ligand plane towards the apical halide anion. The high-spin manganese(II) ions exhibit a very weak intramolecular ferromagnetic exchange interaction (J=+0.1 to +0.3 cm–1) in all four complexes. [Mn2L1(MeCO2)]ClO4 and [Mn2L2(MeCO2)]ClO4 include binuclear units bridged by acetate anions into infinite chains. The manganese ions are displaced out of the macrocyclic ligand plane towards the acetato oxygen atom and the co-ordination geometry is essentially square pyramidal. The high-spin manganese(II) ions exhibit a weak intramolecular antiferromagnetic exchange interaction (J=–0.8 cm–1) in both complexes. The extended intermolecular interaction mediated by the acetato groups between the manganese ions of a chain is very weak but still reflected by the powder e.s.r. spectra. [Mn2L3]ClO4 is most probably built from tetranuclear species including two binuclear units bridged through their alcholate anions. The high-spin manganese(II) ions of this complex are involved in intramolecular antiferromagnetic exchange interactions stronger than those usually reported for manganese(II). [Mn2L1(MeCO2)]ClO4, [Mn2L2(MeCO2)]ClO4, and ([Mn2L3]ClO4)2 are the first antiferromagnetically exchange-coupled manganese(II) complexes including Robson-type ligands.