Silver(I), Zinc(II) and Gallium(III) thiophene-2-carboxylates: Synthesis, solution and solid state characterization...

Three 2-thiophenecarboxylate (Tio2c) complexes with different central atoms Ag(I), Zn(II) and Ga(III), [Ag(Tio2c)]₂ (AgTio2c), {[Zn₂(Tio2c)₄]₂}_n (ZnTio2c) and [Ga(Tio2c)₃]·H₂O (GaTio2c), were synthesized and elemental, spectral and thermal analyses were used for their characterization. The AgTio2c and ZnTio2c single crystal structures confirmed the most common bidentate bridging coordination mode with typical strong argentophilic interactions in the case of AgTio2c complex. Complexes' stability in biological test stock solution were confirmed by ¹H NMR spectroscopy. Potentiometric data analysis by BSTAC program resulted in the determination of the stability constants of four complex species, [Zn(Tio2c)]⁺ (log β₁₁₀ = 2.06 ± 0.04), [Zn(Tio2c)(OH)] (log β_11-1 = -5.0 ± 0.1), [Zn(Tio2c)(OH)₂]^- (log β_11-2 = -12.9 ± 0.4) and [Zn(Tio2c)₂(OH)₂]^2- (log β_12-2 = -8.54 ± 0.04) with low abundance in aqueous solution. Theoretical estimation of the complex species in aqueous solution indicates a rather monodentate Tio2c coordination mode in the [Zn(Tio2c)]⁺ species, while the hydroxido complex species prefer a rather bidentate O,O'-bond of the carboxylate. Antimicrobial and anticancer bioassays clearly confirmed the highest biological activity (toxicity) of the AgTio2c complex. The activity of ZnTio2c was slightly higher (or the same) compared to GaTio2c. The HSA (human serum albumin) binding behaviour of the AgTio2c, ZnTio2c and GaTio2c complexes was investigated using fluorescence spectroscopy and results revealed that the calculated K_b values were in the order of 10⁴ M^-1.