Synthesis, crystal structure and in vitro antibacterial activity of two novel silver(I) complexes

Two silver(I) complexes [Ag2(dppm)2(L1)2(CH2Cl2)2] (1) and [Ag4(dppm)2(L2)2(NO3)2] (2) have been prepared by the reactions of [Ag2(dppm)2(NO3)2] with HL1 and HL2 [dppm = bis(diphenylphosphino)methane, HL1 = 2-(9H-carbazol-9-yl) acetic acid and HL2 = (E)-3-(4-(9H-carbazole-9-yl) phenyl) acrylic acid], respectively. Both complexes have been structurally characterized by X-ray crystallography, confirming that 1 is a binuclear complex whereas 2 is a tetranuclear one. Both complexes were assayed for antibacterial activity against two Gram-positive bacterial strains (Bacillus subtilis ATCC 6633 and Staphylococcus aureus ATCC 6538) and two Gram-negative bacterial strains (Pseudomonas aeruginosa ATCC 13525 and Escherichia coli ATCC 35218) by MTT method. Complex 2 exhibited powerful antibacterial activities against B. subtilis ATCC 6633 with MIC of 0.78 μg/mL, which was superior to the positive controls penicillin G. On the basis of the biological results, structure-activity relationships were discussed.