The non-toxic inorganic antimicrobial agents iodine (I2) and copper (Cu) are interesting alternatives for biocidal applications. Iodine is broad-spectrum antimicrobial agent but its use is overshadowed by compound instability, uncontrolled iodine release and short-term effectiveness. These disadvantages can be reduced by forming complex-stabilized, polymeric polyiodides. In a facile, in-vitro synthesis we prepared the copper-pentaiodide complex [Cu(H2O)6(12-crown-4)5]I6 ´ 2I2, investigated its structure and antimicrobial properties. The chemical structure of the compound has been verified. We used agar well and disc-diffusion method assays against nine microbial reference strains in comparison to common antibiotics. The stable complex revealed excellent inhibition zones against C. albicans WDCM 00054, and strong antibacterial activities against several pathogens. [Cu(H2O)6(12-crown-4)5]I6 ´ 2I2 is a strong antimicrobial agent with an interesting crystal structure consisting of complexes located on an inversion center and surrounded by six 12-crown-4 molecules forming a cationic substructure. The six 12-crown-4 molecules form hydrogen bonds with the central Cu(H2O)6 . The anionic substructure is a halogen bonded polymer which is formed by formal I5− repetition units. The topology of this chain-type polyiodide is unique. The I5− repetition units can be understood as a triodide anion connected to two iodine molecules.

Antibiotic resistance toward commonly used medicinal drugs is a dangerously growing threat to our existence. Plants are naturally equipped with a spectrum of biomolecules and metabolites with important biological activities. These natural compounds constitute a treasure in the fight against multidrug-resistant microorganisms. The development of plant-based antimicrobials through green synthesis may deliver alternatives to common drugs. Lepidium sativum L. (LS) is widely available throughout the world as a fast-growing herb known as garden cress. LS seed oil is interesting due to its antimicrobial, antioxidant, and anti-inflammatory activities. Nanotechnology offers a plethora of applications in the health sector. Silver nanoparticles (AgNP) are used due to their antimicrobial properties. We combined LS and AgNP to prevent microbial resistance through plant-based synergistic mechanisms within the nanomaterial. AgNP were prepared by a facile one-pot synthesis through plant-biomolecules-induced reduction of silver nitrate via a green method. The phytochemicals in the aqueous LS extract act as reducing, capping, and stabilizing agents of AgNP. The composition of the LS-AgNP biohybrids was confirmed by analytical methods. Antimicrobial testing against 10 reference strains of pathogens exhibited excellent to intermediate antimicrobial activity. The bio-nanohybrid LS-AgNP has potential uses as a broad-spectrum microbicide, disinfectant, and wound care product.