Solid-state structure and antimicrobial and cytotoxicity studies of a cucurbit[6]uril-like Cu6L4 constructed from 3,5-bis[(1H-tetrazol-5-yl)methyl]-4H-1,2,4-triazol-4-amine

Abstract

3,5-Bis[(1H-tetrazol-5-yl)methyl]-4H-1,2,4-triazol-4-amine (H₂L) associates under deprotonation with CuSO₄ in aqueous medium to form a new waisted barrel-shaped M₆L₄ cluster, namely hexaaquatetrakis{μ₄-3,5-bis[(1H-tetrazol-5-yl)methyl]-4H-1,2,4-triazol-4-amine}-μ₄-sulfato-hexacopper(II) sulfate hydrate, [Cu₆(SO₄)(C₆H₆N₁₂)₄(H₂O)₆]SO₄·nH₂O (n = ∼23) (1). Cluster 1 resembles concave cucurbit[6]uril and has one disordered sulfate anion trapped inside the cage, which additionally stabilizes the Cu₆ unit. The Cu^II ions have either a square-pyramidal or a distorted octahedral geometry. The equatorial positions are filled by N atoms from the L^2- ligand, while the axial positions are occupied by coordinated water molecules and O atoms of the sulfate counter-ion. In the solid state, the Cu₆ clusters are connected through a large number of hydrogen bonds formed by uncoordinated water molecules and an additional sulfate anion. The compound shows good antimicrobial activity against E. coli tested with the Kirby Bauer approach. In addition, the cell viability towards HeLa and L-929 cells was studied.

Keywords: antimicrobial Cu compound; barrel-type complex; copper cluster; crystal structure; cytotoxicity.