Synthesis, a case of isostructural packing, and antimicrobial activity of silver(I)quinoxaline nitrate, silver(I)(2,5-dimethylpyrazine) nitrate and two related silver aminopyridine compounds

The synthesis and low temperature crystal structures of [Ag(quinoxaline)]_n(NO₃)_n, 1, [Ag(2,5-dimethylpyrazine)(NO₃)]_n, 2 and [Ag₄(3-aminopyridine)₄(NO₃)₄]_n 3 are presented. The quinoxaline compound forms a 1D coordination polymer with the characteristic linear 2-coordination figure of silver(I), the N–Ag–N angle being 164.2(1)°, and only weak silver–nitrate interactions. In addition there is an interaction giving pairs of parallel chains as the main structural theme. The 2,5-dimethylpyrazine compound has approximately trigonal-planar coordination, also binding one nitrate at the relatively short Ag–O distances 2.444(3)Å and 2.484(3)Å, respectively, for the two crystallographically different silver atoms. This also results in a 1D coordination polymer that, despite the large differences in the Ag(I) coordination environment, is isostructural with 1. [Ag₄(3-aminopyridine)₄(NO₃)₄]_n 3 forms a 2D coordination polymer by bridging nitrate ions. The antimicrobial activity of 1–3, and also of [Ag₃(2-aminopyridine)₄](NO₃)₃, 4 was screened for 13 different pathogens and substantial activity was shown for 1 against Escherichia coli and Pseudomonas aeruginosa (MIC 4 µg cm^–3) and somewhat lower activity was registered against Sarcina lutea and Salmonella typhi for 1, Bordetella bronchiseptica for 2, Salmonella typhi and Pseudomonas aeruginosa for 3, and Escherichia coli and Shigella sonnie for 3 (MIC 8 µg cm^–3). Only low activity was shown against the yeast Candida albicans for 1, 2 and 4 whereas no activity against this pathogen was registered for 3