| Abstract |
The reactivity of the shortened salen-type ligands H 3 salmp, H 2 salmen and H 2 sal( p -X)ben with variable para -substituent on the central aromatic ring (X = t Bu, Me, H, F, Cl, CF 3 , NO 2 ) towards the trivalent metal ions manganese(III) and iron(III) is presented. The selective formation of the dinuclear complexes [M 2 (-salmp) 2 ], M = Mn ( 1a ), Fe ( 2a ), [M 2 (-salmen) 2 (-OR) 2 )], R = Et, Me, H and M = Mn ( 3a – c ) or Fe ( 4a – c ), and (M 2 (-sal[ p -X]ben) 2 (-OMe) 2 ), X = t Bu, Me, H, F, Cl, CF 3 , NO 2 and M = Mn ( 5a – g ) or Fe ( 6a – g ), could be identified by reaction of the Schiff bases with metal salts and the base NEt 3 , and their characterization through elemental analysis, infrared spectroscopy, mass spectrometry and single-crystal X-ray diffraction of 2a 2AcOEt, 2a 2CH 3 CN and 3c 2DMF was performed. In the case of iron(III) and H 3 salmp, when using NaOH as a base instead of NEt 3 , the dinuclear complexes [Fe 2 (-salmp)(-OR)(salim) 2 ], R = Me, H ( 2b – c ) could be isolated and spectroscopically characterized, including the crystal structure of 2b 1.5H 2 O, which showed that rupture of one salmp 3– to two coordinated salim – ligands and release of one salH molecule occurred. The same hydrolytic tendency could be identified with sal( p -X)ben ligands in the case of iron(III) also by using NEt 3 or upon standing in solution, while manganese(III) did not promote such a C–N bond breakage. Cyclic voltammetry studies were performed for 3b , 4b , 5a and 6a , revealing that the iron(III) complexes can be irreversibly reduced to the mixed-valence Fe II Fe III and Fe II 2 dinuclear species, while the manganese(III) derivatives can be reversibly oxidized to either the mixed-valence Mn III Mn IV or to the Mn IV 2 dinuclear species. The super-exchange interaction between the metal centers, mediated by the bridging ligands, resulted in being antiferromagnetic (AFM) for the selected dinuclear compounds 3b , 4b , 5a , 5e, 5f , 6a and 6e . The coupling constants J (–2 J Ŝ 1 · Ŝ 2 formalism) had ...
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