English abstract
Several aroylhydrazone ligands were synthesized by the Schiff-base condensation reaction of an aldehyde or a ketone with an aroylhydrazide bearing a substituent group in position 2 or 4. The key ligands were H2(3,5-'Buz)L' (from the relevant aldehyde), H2(5-R)-L? (from 2'-hydroxyacetophenone derivatives), H2L" (from 2'hydroxypropiophenone) and HL* [from di(2-pyridyl) ketone or 2-acetyl-4-methyl pyridine]. The chemical identities of these ligands were ascertained by microanalyses and mass spectrometry. Vibrational and 'H-NMR spectroscopic techniques confirmed that these aroylhydrazones are isolated in the keto tautomeric form. These ligands demonstrate remarkable coordination versatility towards manganese due to their propensity to undergo tautomeric transformations imposed by the transition metal ion and triggered by the base in the reaction mixture. Each of these aroylhydrazones was treated with (O2CCH3)2Mn:4H2O in stoichiometric amounts under refluxing and aerobic conditions to produce new bis(chelate) Mn(II), novel mixed-tautomer bis(chelate) Mn(III), ternary Mn(III), dinuclear Mn(III) and novel bis(chelate) Mn(IV) aroylhydrazone complexes. These complexes were characterized by pertinent analytical and spectroscopic methods.
The molecular structures of [Mn" (py-L--NO2)2] (1), [Mn"{(3,5-Buz)-L'{H(3,5'Buz)-sal}(OH)) (2), [Mn"" {H(3,5-'Buz)-L--OMe}{(3,5-Buz)-L--OMe}] (3), [Mn'"(5-NO2-L2-NO2)(MeOH)(u-OMe)], (4) and [Mn" (L')2] (5) were determined by single-crystal X-ray diffraction. The X-ray structure of 1 revealed a bis(chelate) manganese(II) complex possessing a severely distorted octahedral MnN4O2 coordination sphere. Compound 2 is a ternary Mn" complex with H(3,5-'Bu2)L'enolate), (3,5-'Buz)-sal (aldehyde anion) and an aqua ligand forming an axially elongated octahedral geometry. Compound 3 represents the first example of a crystallographically elucidated bis(chelate) manganese(III) aroylhydrazone complex and its special features are the mixed keto-enolate coordination and the demonstration of the Jahn-Teller distortion. The X-ray structure of complex 4 revealed a centrosymmetric dinuclear manganese(III) complex with two methoxide bridges; the Mn" centres are in an axially elongated octahedral geometry in accordance with the tetragonal distortion. Compound 5 is a novel bis(chelate) manganese(IV) aroylhydrazone complex with two-fold symmetry of a distorted octahedral geometry.
The effective magnetic moments of the manganese complexes revealed an interesting trend. The pyridyl aroylhydrazones stabilized the divalent state (high-spin d', S = 5/2) of manganese whereas the phenolic aroyihydrazones favoured the trivalent (high-spin d", S = 2) and tetravalent (d', S= 3/2) states of manganese. The 3,5-'Buzsubstituted complexes are all in the +3 state. On the other hand, for the monosubstituted complexes, the electron-donating groups in the para-position of the phenolic ring invariably stabilize the +4 state of manganese whereas the electronwithdrawing groups stabilize the +3 state. The RT effective magnetic moment of [Mn"(5-NO2-LA-NO2)(MeOH)(u-OMe)], (4) (Metf = 6.71 MB) is consistent with two non-interacting high-spin Mn(III) ions. By modulating the ligand propertieprincipal oxidation states of manganese were accessed in this aroylhydrazon system.
