Synthesis and structural studies of dioxomolybdenum(VI) complexes with isoniazid-related hydrazones

Abstract

The chemistry of hydrazones is continuing to be an interesting area of research because of their modularity, easiness of synthesis and stability towards hydrolysis.[1−3] Synthesis of the dioxomolybdenum(VI) complexes [MoO2(HLR) (MeOH)]Cl (1−3), was carried out using MoO2Cl2 and the corresponding aroylhydrazone ligand H2LR (salicylaldehyde isonicotinoylhydrazone (H2LSIH), 2-hydroxy-naphthaldehyde isonicotinoylhydrazone (H2LNIH), or p-(N, N’- diethylaminosalicylaldehyde isonicotinoylhydrazone (H2LEt2NSIH) in methanol. Compounds [MoO2(HLR)(H2O)]Cl (1a−3a) obtained upon exposure of the coresponding mononuclear complexes 1-3 to moisture were also investigated. Deprotonation of the mononuclear complexes [MoO2(HLR)(MeOH)]Cl (1−3), was performed using Et3N as a base (by conventional solution based-method and mechanochemical aproach) as well as by UV-light assisted reactions yielding [MoO2(LSIH)(MeOH)] (4) [4], [MoO2(LNIH)(MeOH)] (5) and [MoO2(LEt2NSIH)]n (6), respectively. Crystal and molecular structures of all complexes were solved by the single-crystal X-ray diffraction method. In all complexes the ligand coordinates the metal centre of the cis-MoO22+ core tridentately via phenolic-oxygen, azomethine-nitrogen and ketohydrazone oxygen forming five and six member chelate rings. The remaining sixth coordination site of the distorted octahedron is occupied by the oxygen atom of the solvent molecule (methanol in 1-3 and 5, water in 1a −3a) or nitrogen atom of the bridging izonicotinyl moiety of the neighboring complex (in 6). We were interested to investigate importance of nonbonding interactions in the structures, especially the ability of these complexes to form different hydrogen bonding motifs depending on the protonation state of the complexes.