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General References: Holm, R. H.; Everett, G. W., Jr.; Chakravorty, A.; Metal Complexes of Schiff Bases and ß-Ketoamines, Progr. Inorg. Chem. 7 [1966] 83/214, 120. Lawrence, G. D.; Sawyer, D. T.; The Chemistry of Biological Manganese, Coord. Chem. Rev. 27 [1978] 173/93, 182. Connors, H.; McAuliffe, C. A.; Tames, J.; Manganese Schiff Base Complexes, Rev. Inorg. Chem.3 [1981] 199/257.General Aspects. The Schiff base complexes described in this chapter are derived from ligands obtained by the reaction of aldehydes or ketones with amines. Ligation to manganese occurs through the nitrogen atom of the azomethine group (:::C=N-), as weil as through other functional groups present in the ligand, such as hydroxy and carboxy groups or other groups containing nitrogen or sulfur donor atoms. These functional groups can be either on the carbonyl moiety or on the amine moiety or on both sides of the Schiff base molecule, resulting in a variety of di-or pOlydentate chelating ligands. Ligands with higher denticity are derived from oxo compounds and di-or polyamines or from dioxo compounds and amines. The formation of several five-or six-membered chelate rings by coordination of the di-or polydentate ligands is the cause of the stabilizing effect of Schiff bases particularly on manganese in the three-or four-oxidation state. Most of the complexes treated in this chapter are those with Schiff bases derived from salicylaldehyde or its derivatives. Depending upon the nature and the position of the ring substituents, a markedly different behavior of these ligands is observed.Generally, the Mn" complexes are prepared from a manganese salt and the Schiff base or by reaction of a manganese salt with the aldehyde or ketone and the amine in alcoholic or aqueous alcoholic solution in an inert atmosphere. In the IR spectra, coordination of the azomethine nitrogen atom is reflected by a shift of the free ligand v(C=N) band (in the region 1650 to 1630 cm-1 ) to lowerwave numbers. Forthe large group ofcomplexes with Schiff bases derived from hydroxyaldehydes, coordination of the hydroxy oxygen to Mn is indicated by disappearance of the v(OH) band (in the region 3400 to 3200 cm-1 ) and a shift of the free ligand v(C-O) band (at -1300 cm-1 ) to higher wave numbers. Usually, the ligand donor atoms are arranged in the equatorial positions of the coordination sphere with anions or additional solvent molecules in many cases occupying the apical sites. The resulting molecular structures are square pyramidal, trigonal bipyramidal, or octahedral. Magnetic measurements indicate in almost all cases high-spin complexes and for part of them antiferromagnetic or ferromagnetic interactions of the Mn atoms in dinuclear or polynuclear compounds with bridging alkoxide or phenoxide oxygen atoms. A typical structure of a dinuclear manganese(lI) complex is that of a hydrated complex with a tridentate Schiff base derived from salicylaldehyde and an aminophenol, shown below schematically:
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