Silver(I)-barbital based frameworks: Syntheses, crystal structures, spectroscopic, thermal and antimicrobial activity studies

Three novel polymeric complexes in the silver(I)-barbital (barb) system with the formulae Na3[Ag3(μ-barb)6] (1), {[Ag2(μ-barb)2][Ag2(μ-en)2] ·  5H2O}n (2) and [Ag(barb)(μ-bpe)]n (3) [barb = 5,5-diethylbarbiturato; en = ethylenediamine; bpe = trans-1,2-bis(4-pyridyl)ethylene] have been synthesized and characterized by elemental analyses, IR, 1H NMR, DTA-TG and single-crystal X-ray diffraction. The structure of 1 reveals a 2D supramolecular arrangement of [Ag(barb)2] units by means of H-bond interactions, and the barb anions act as a bridge between the sodium(I) cations through the carbonyl groups, giving rise to a 3D network. Bi- and tridentate bridging modes of the barb ligand were observed simultaneously in 1. Silver(I) is linearly coordinated by two N atoms of two barb ligands, while sodium(I) has a highly distorted {NaO6} coordination geometry by barb O atoms. The average Ag⋯Na separation of 3.58 (5) Å possibly indicates a kind of ‘metallophilic’ interaction between Ag and Na atoms. Complex 2 consists of 1D anionic and cationic chains interconnected by way of Ag⋯Ag interactions leading to an unusual 2D grid-type framework, which is further extended to a 3D network with open channels by extensive hydrogen bonds. Complex 2 also exhibits some unusual features, such as the presence of the barb dianion and its bidentate bridging mode via the both negatively charged N atoms. Complex 3 is a 1D coordination polymer, in which the bpe ligand acts as a bridging ligand, while the barb ligand is monodendately N-coordinated resulting in a tri-coordinate silver(I) centre. Spectral and thermal analysis data for 1–3 are in agreement with the crystal structures. While none of the barb ligands and other coligands showed any significant antimicrobial activity, complexes 1–3 exhibited a wide spectrum of antimicrobial activity against the bacteria and fungi tested.

Three AgI-barb coordination polymers have been reported. Na3[Ag3(μ-barb)6] is a 3D mixed-metal complex, while {[Ag2(μ-barb)2][Ag2(μ-en)2] · 5H2O}n contains the barb dianion and features 2D grid-type layers, which are further connected by extensive hydrogen bonds resulting in a 3D framework with open channels. [Ag(barb)(μ-bpe)]n consists of 1D helical chains connected by hydrogen bonds between barb ligands to form 2D supramolecular sheets, which are further linked by aromatic π–π stacking interactions into a 3D network. The barb ligand has been shown to be able to exhibit different coordination modes. Different coordination modes of barb are seen in Na3[Ag3(μ-barb)6] and {[Ag2(μ-barb)2][Ag2(μ-en)2] · 5H2O}n. Antimicrobial studies of the title complexes were also performed. While barb and the other coligands did not show any significant antimicrobial activity, complexes 1–3 exhibited a wide spectrum of antimicrobial activity against selected bacteria and fungi.Figure optionsDownload as PowerPoint slide