On zinc(ii) coordination chemistry with furosemide: a journey from a mononuclear complex to a coordination polymer

Abstract

In continuation of our studies on zinc(II) coordination chemistry, reactions between the zinc(II) starting material and furosemide were investigated. Furosemide, a well-known pharmaceutical, contains functional groups which could serve as donors in coordination with metal ions. Reactions between zinc oxide or chloride and furosemide in aqueous ammonia solution yielded a mononuclear complex, [Zn(NH₃)₂(fur)₂] (1), where fur⁻ stands for deprotonated furosemide. Unfortunately, some reactions produced mixtures of the desired metal complex 1 and by-product, ammonium salt NH₄fur (2). To further explore the coordination chemistry of furosemide, quinaldinate (an anion of quinoline-2-carboxylic acid, abbreviated as quin⁻) was introduced into the reaction system, resulting in the formation of a coordination polymer, [Zn₃(quin)₄(fur)₂]_n·2nCH₃OH (3). 1 and 3 were evaluated for their antibacterial properties against Gram-positive and Gram-negative bacteria. Notably, compound 3 exhibited moderate antibacterial activity against Staphylococcus epidermidis, representing a promising starting point for the preparation of potential antibacterial zinc(II) complexes.