Antibacterial Action of 4,4′-Bipyrazolyl-Based Silver(I) Coordination Polymers Embedded in PE Disks

Coupling the rigid spacer 4,4′-bipyrazole (H2BPZ), in its anionic or neutral form, to different silver­(I)
salts
allowed isolation of the novel coordination polymers [Ag2(BPZ)] (1) and [Ag­(H2BPZ)­(X)] (X = NO3, 2; ClO4, 3; BF4, 4; PF6, 5; CH3SO3, 6; CF3SO3, 7), which were fully characterized by infrared and emission
spectroscopies, thermal analysis, and X-ray powder diffraction. The
crystal structure of 1 consists of 2-D layers containing
1-D chains of Ag­(I) ions bridged by exo-tetradentate
bipyrazolato moieties. The crystal structures of the [Ag­(H2BPZ)­(X)] species 2–7 feature 1-D
chains of [Ag­(H2BPZ)] stoichiometry, along which the metal
centers are bridged by exo-bidentate bipyrazolyl
spacers. Contacts among adjacent chains are mediated by the counterions
through nonbonding interactions involving the Ag­(I) ions and the pyrazolyl
N–H groups. Thermogravimetric analyses disclosed the good thermal
stability of these materials, decomposing in the range 200–300
°C. Under UV irradiation at room temperature, all the species
showed a yellow-green emission centered in the range 520–522
nm. When embedded into polyethylene disks, 1, 2, and 4–7 demonstrated their activity
as topical antibacterial agents against suspensions of E.
coli, P. aeruginosa, and S. aureus: complete reduction of the three bacterial strains was achieved
in 24 h, reduction of S. aureus reaching ca. 90%
in only 2 h. Biocidal action was expressed also by contact susceptibility
tests.