Control of the geometry and anisotropy driven by the combination of steric and anion coordination effects in CoII complexes with N6-tripodal ligands: the impact of the size of the ligand on the magnetization relaxation time

Four mononuclear CoII complexes of formula [Co(L)(SCN)2(CH3OH)0.5(H2O)0.5]·1.5H2O·0.75CH3OH (1), [Co(L1)Cl2]·H2O·2CH3CN (2), [Co(L1)(SCN)2]·1.5H2O·CH3OH (3) and [Co(L1)]ClO4·2CH3OH (4) were prepared from the N6-tripodal Schiff base ligands (S)P[N(Me)NC(H)2-Q]3 (L) and (S)P[N(Me)NC(H)1-ISOQ]3 (L1), where Q and ISOQ represent quinolyl and isoquinolyl moieties, respectively. In 1, the L ligand does not coordinate to the CoII ion in a tripodal manner but using a new N,N,S tridentate mode, which is due to the fact that the N6-tripodal coordination promotes a strong steric hindrance between the quinolyl moieties. However, L1 can coordinate to the CoII ions either in a tripodal manner using CoII salts with poorly coordinating anions to give 4 or in a bisbidentate fashion using CoII salt-containing medium to strongly coordinating anions to afford 2 and 3. In the case of L1, there is no steric hindrance between ISOQ moieties after coordination to the CoII ion. The CoII ion exhibits a distorted octahedral geometry for compounds 1-3, with the anions in cis positions for the former and in trans positions for the two latter compounds. Compound 4 shows an intermediate geometry between an octahedral and trigonal prism but closer to the latter one. DC magnetic properties, HFEPR and FIRMS measurements and ab initio calculations demonstrate that distorted octahedral complexes 1-3 exhibit easy-plane magnetic anisotropy (D > 0), whereas compound 4 shows large easy-axis magnetic anisotropy (D < 0). Comparative analysis of the magneto-structural data underlines the important role that is played not only by the coordination geometry but also the electronic effects in determining the anisotropy of the CoII ions. Compounds 2-3 show a field-induced slow relaxation of magnetization. Despite its large easy-axis magnetic anisotropy, compound 4 does not show significant slow relaxation (SMR) above 2 K under zero applied magnetic fields, but its magnetic dilution with ZnII triggers SMR at zero field. Finally, it is worth remarking that compounds 2-4 show smaller relaxation times than the analogous complexes with the tripodal ligand bearing in its arms pyridine instead of isoquinoline moieties, which is most likely due to the increase of the molecular size in the former one.

Silver sulfadiazine–immobilized celluloses as biocompatible polymeric biocides

Sulfadiazine was immobilized onto cotton cellulose using ethylene glycol diglycidyl ether as a binder. Upon treatment with diluted silver nitrate aqueous solution, the sulfadiazine moieties in the immobilized celluloses were transformed into silver–sulfadiazine coordination complexes. The resulting silver sulfadiazine–immobilized celluloses provided a 6-log reduction of 108 CFU mL−1 of Staphylococcus aureus (Gram-positive bacteria), Escherichia coli (Gram-negative bacteria), methicillin-resistant Staphylococcus aureus (drug-resistant bacteria), vancomycin-resistant Enterococcus faecium (drug-resistant bacteria), and Candida albicans (fungi) in 30–60 minutes, and a 5-log reduction of 107 PFU mL−1 of MS2 virus in 120 minutes. The antibacterial, antifungal, and antiviral activities were both durable and rechargeable. Additionally, trypan blue assay suggested that the new silver sulfadiazine–immobilized celluloses sustained excellent mammal cell viability, pointing to great potentials of the new materials for a broad range of health care–related applications.