Further attempts to rationalise the co-ordination chemistry of manganese with Schiff base ligands and supplementary carboxylate donors

Some manganese(III) complexes of Schiff base ligands with ancillary carboxy late donors have been found to exhibit structural diversity, although some patterns emerged. Thus, when the ligands 3CH(3)O-salen and 3CH(3)O-salpn [3 CH(3)O-salen = dianion of N,N'-bis(3-methoxysalicylidene)ethane-1,2-diamine , 3CH(3)O-salpn = dianion of N,N'-bis(3-methoxysalicylidene)propane-1,3-dia mine] are used in conjunction with carboxylates RCO2- (R = Me, Et, Pr-n or CH2Ph) unidentate carboxylate bonding occurs as in the crystallographically observed [Mn(3CH(3)O-salen)(O2CMe)-(H2O)]. 2H(2)O 1, [Mn(3CH(3)O-salen)(O2 CCH2Ph)(H2O)]. H2O 4, and [Mn(3CH(3)O-salpn)(O2CCH2Ph)(H2O)] 5. On the othe r hand, employing the more sterically encumbered carboxylates (BuCO2-)-C-t and (PrCO2-)-C-i, bidentate chelating binding of the carboxylate occurs, as in [Mn(3CH(3)O-salpn)(O2CBut)] 2 and [Mn(3CH(3)O-salpn)(O2CPri)] 3. The re activity of [Mn(salpn)(acac)] (acac = acetylacetonate) with Me3SiCl and ali phatic carboxylic acids, RCO2H (R = Me, Et, Pr-n, Bu-n, Pr-i or Bu-t), has also been investigated. A dimer species [{Mn(salpn)Cl}(2)]. CH3CN 6 was iso lated from the reaction of Me3SiCl with [Mn(salpn)(acac)] while the carboxy lic acids seem to lead to the isolation of monomers, such as [Mn(salpn)(O2C Pri)] 7. This synthetic route has also been applied to the preparation of r elated complexes, in which the manganese(III) centre is not attainable with reliability via the aerobic oxidation of a manganese(II) precursor, althou gh some rare examples have been obtained by the latter method, such as [Mn( 5NO(2)-salen)(O2CMe)(H2O)], 8, [5NO(2)-salen = dianion of N,N'-bis(5-nitros alicylidene)ethane-1,2-diamine]). Single crystals were grown from a dimethy lformamide solution of the material of stoichiometry Mn(3Br,5NO(2)-salpn)(O 2CMe). H2O [3Br,5NO(2)-salpn = dianion of N,N'-bis(3-bromo-5-nitrosalicylid ene)propane-1,3-diamine], isolated from this route and found to consist of the unexpected [{Mn(mu-3Br,5NO(2)-salpn)(mu-O)}(2)]. 3DMF 9, apparently con taining a manganese(IV) species, in spite of the electron withdrawing natur e of the substituents on the aromatic rings of the ligand.