Spectroscopic properties and antimicrobial activity of dioxomolybdenum(VI) complexes with heterocyclic S,S'-ligands

Abstract

Five new dioxomolybdenum(VI) complexes of the general formula [MoO2(Rdtc)2], 1-5, where Rdtc- refer to piperidine (Pipdtc), 4-morpholine (Morphdtc), 4-thiomorpholine (Timdtc), piperazine (Pzdtc) or N-methylpiperazine (N-Mepzdtc) dithiocarbamates, respectively, have been prepared. The complexes were characterized by elemental analysis, conductometric measurements, electronic, IR and NMR spectroscopy. The complexes 1-5 contain a cis-MoO2 group and have an octahedral geometry. Two dithiocarbamato ions join as bidentates with both the sulfur atoms to the molybdenum atom. The presence of different heteroatoms in the piperidino moiety influences the v(C=N) and v(C=S) vibrations, which wavelengths decrease in the order: Pipdtc > N-Mepzdtc > Morphdtc > Pzdtc > Timdtc ligands. Based on their spectral data, the molecular structures of complexes 1-5 were optimized at the semi-empirical molecular-orbital level, and the geometries, as obtained from calculations, are described. The antimicrobial activities of the complexes were tested against nine different laboratory control strains of bacteria and two strains of the yeast Candida albicans. All the tested strains were sensitive. Complexes bearing heteroatom in position 4 of piperidine moiety were significantly more potent against the tested bacteria compared to the corresponding ligands.

Sintetisano je pet novih dioksomolibden(VI) kompleksa, opšte formule [MoO2(Rdtc-)2], sa Rdtc- ligandima: piperidin- (Pipdtc), 4-morfolin- (Morphdtc), 4-tiomorfolin- (Timdtc), piperazin- (Pzdtc) i N-metilpiperazin- (N-Mepzdtc) ditiokarbamatima. Kompleksi su okarakterisani elementalnom analizom, IR i NMR spektroskopijom kao i merenjem molarne provodljivosti. Pretpostavljena geometrija svih kompleksa je oktaedarska. Rdtc- ligandi su bidentatno koordinovani preko oba atoma sumpora za atom molibdena. Prisustvo različitih heteroatoma utiče na promenu položaja v(C=N) i v(C=S) vibracija, čiji opada sledećim redom liganada: Pipdtc > N-Mepzdtc > Morphdt > Pzdtc > Timdtc. Na osnovu spektralnih podataka, strukture svih kompleksa su optimizovane na semiempirijskom molekulsko-orbitalnom nivou upotrebom PM6 metoda. Antimikrobna aktivnost ispitivana je na jedanaest različitih patogena. Uočeno je da kompleksi koji imaju heteroatom u položaju 4 piperidinskog prstena ispoljavaju značajno veću jačinu antimikrobnog dejstva prema bakterijama, u poređenju sa odgovarajućim ligandima.