Studies of the binding modes of carboxylate donors with manganese(III) complexes containing tetradentate Schiff base ligands. Crystal structures of the complexes [Mn(3-CH3Osalpn)(HO2CC6H4CO2)]n and [{Mn(5-NO2salpn)(OH)(H2O)}{Mn(5-NO2salpn)(HO2CC6H4CO2)(H2O)}]·C2H5OH