Synthesis, characterization and biological applications of bismuth(III) complexes with aroylthiourea ligands

Abstract

This work describes the synthesis, structural characterization and biological applications of three new bismuth(III) complexes with aroylthiourea-based ligands: [Bi(La)3(HLa)] (1), [Bi2(Lb)4(μ-Lb)2]⋅2(C3H6O) (2), and [Bi6(μ-Lc)6(μ3-NO3)2(μ6-NO3)](NO3)3⋅4H2O (3), where HLa = N-benzoyl(N′,N′-diethylthiourea), HLb = N-benzoyl(morpholinylthiourea), and H2Lc = N2,N6-bis(diethylcarbamothioyl)pyridine-2,6-dicarboxamide. The ligands HLa and HLb were considered as monopodal, while H2Lc as bipodal. All compounds were characterized by melting point determination, Fourier-transform infrared spectroscopy (FTIR), proton proton and carbon-13 nuclear magnetic resonance spectroscopy (NMR), mass spectrometry (MS), elemental analysis (EA) and single-crystal X-ray diffraction (SC-XRD). Structural analysis showed that compound 1 was a mononuclear heptacoordinate complex, while compound 2 presented a dinuclear structure and compound 3 was built up by a hexanuclear framework. The proligands, the new complexes, and Bi(NO3)3⋅5H2O had their antibacterial activities evaluated against E. coli (ATCC 25922), S. aureus (ATCC 25923), and P. aeruginosa (ATCC 27853). The in vitro disk-diffusion (DD) method showed the ability of compound 2 to inhibit two types of bacteria (P. aeruginosa and S. aureus). In the results of minimum inhibitory concentration (MIC), all complexes showed significant activity against the tested microorganisms except for compound 1. The inorganic salt used for comparison showed antibacterial activity only against P. aeruginosa and the ligands showed no apparent activity. Compound 2 presented the best antibacterial activity among the tested substances, and its performance was remarkable even when compared to other similar compounds found in the literature, attesting the importance of targeting bismuth(III) aroylthioureas for further research on new drugs development.