Mono- and penta-nuclear self-assembled silver(I) complexes of pyrazolyl s-triazine ligand; synthesis, structure and antimicrobial studies

The self-assembled [Ag (PTDM)NO ₃] (1), [Ag (PTDM) ₂(H ₂O)]ClO ₄ ^.H ₂O (2) and [Ag ₅(PTDM) ₄(H ₂O) ₆(ClO ₄) ₄]ClO ₄ ^.2H ₂O (3) complexes were synthesized by the direct mixing of AgX (X = NO ₃¯ or ClO ₄¯) and 4,4′-[6-(3,5-dimethyl-1H-pyrazol-1-yl)-1,3,5-triazine-2,4-diyl]dimorpholine (PTDM) ligand in water–methanol mixture. The coordination numbers of silver range from three to five. Complex 3 is a rare case in which one nitrogen atom from the same s-triazine core of the PTDM ligand has a μ(1,1) bridging mode between Ag1 and Ag2 in the penta-nuclear array with Ag1–N1 and Ag2–N1 distances of 2.666(4) and 2.418(3) Å, respectively. Its 3D topology has a kind of primitive dense packing derived from the α-Po type structure. Hirshfeld analysis showed that the percentages of the O ^…H hydrogen bonds were 32.4, 25.4, and 42.0% in complexes 1–3, respectively. While the ligand showed no antimicrobial activity at the applicable concentration, the penta-nuclear complex 3 had higher antibacterial (MIC = 3.7 μmol/L) and antifungal (14.6 μmol/L) potencies toward the tested microbes compared with complexes 1 and 2. Also, the killing doses of 3 were in the range of 7.3–58.5 μmol/L compared with 18.2–291.1 and 20.1–160.6 μmol/L for 1 and 2, respectively. It is clear that the higher Ag-content in 3 could be the main reason for its higher antimicrobial activity.