Synthesis and Structural Studies on some Dioxomolybdenum (VI) Complexes Bearing 1-(1-Hydroxynaphthalen-2-yl) Ethanone Moiety

A number of new molybdenum complexes Cis-MoO2(NE)2.CH3OH, Cis-MoO2(HRSB)2.nH2O {R= H, 4-Br, 4-OCH3, 4-CH3 andn= 0, 1, 2} Cis-MoO2(HL)(acac).nH2O {HL= HNEBH, HNEINH, HNENH, HNEPH, n=0, 1}, Cis-[MoO2(L\)2.nH2O], {L\=HNE-2-ABH, HNE-4-ABH, n = 0, 2} and Cis-[Mo2O5(HNEAH)2] have been synthesized and characterization by magnetic,spectroscopic (FT-IR, 1H and 13C-NMR spectra) and electrochemical techniques. The complexes were made reaction ofCis-MoO2(acac)2 with the ligands, (1-hydroxynaphthalen-2-yl)ethenone (HNE), (E)-2-(1-(phenylimino)ethyl)naphthalen1-ol (HASB), (E)-2-(1-(p-tolylimino)ethyl) naphthalen-1-ol (HTSB), E-2-(1-(4-methoxyphenylimino)ethyl)naphthalen-1-ol(HMSB) and (E)-2-(1-(4-bromophenylimino)ethyl)naphthalen-1-ol (HBrSB) monobasic bidentate (NO) or 2-anmino-N/-(1-(1-hydroxynaphthalene-2-yl)ethylidene)benzohydrazide (HNE2-ABH), 4-anmino-N/-(1-(1-hydroxynaphthalene-2-yl)ethylidene)benzohydrazide (HNE4-ABH), N/-(1-(1-hydroxynaphthalene-2-yl)ethylidene)benzohydrazide (HNEBH),N-(1-(1-hydroxynaphthalene-2-yl)ethylidene)acetohydrazide (HNEAH), N/-(1-(1-hydroxynaphthalene-2-yl)ethylidene)nicotinohydrazide (HNENH), N/-(1-(1-hydroxynaphthalene-2-yl)ethylidene)isonicotinohydrazide (HNEINH), N/-(1-(1-hydroxynaphthalene-2-yl)ethylidene)picolinohydrazide (HNEPH), they coordinate as dibasic tridentate (OON).Both the molecular and the spectroscopic studies showed that, the complexes are octahedrally coordinated. The redoxproperties, of the electrode couples and the stability of some complexes towards reduction were linked to the electronwithdrawing or ability releasing of the substituent in the Schiff bases and the hydrazones. Results show that, changesin E1/2 for the complexes due to remote substituent effects could be related to changes in basicity of the carbonyl oxygenof the hydrazide moiety in the hydrazone ligand. The electron-donating substituents stabilized Mo(VI) complexes whileelectron-withdrawing groups favored lower oxidation state of Mo(V) and/ or Mo(IV) species. The nature of mechanismand kinetic parameters of the electroactive chelates are strongly dependent on the substituent. The EHOMO and ELUMOlevel, of hydrazone and some of Cis-molybdenum complexes, from both electrochemical and theoretical data also backdonation energy (ΔEback-donation), ionization potential (I), molecular dipole moment (μ), electronegativity (χ), softness (σ)electron affinity (A), global hardness (η), and electrophilicity index (ω) were calculated.