Silver(I)-Barbital Based Frameworks: Syntheses, Crystal Structures, Spectroscopic, Thermal and Antimicrobial Activity Studies

Abstract

Three novel polymeric complexes in the silver(I)-barbital (barb) system with the formulae Na<inf>3</inf>[Ag<inf>3</inf>(μ-barb)<inf>6</inf>] (1), {[Ag<inf>2</inf>(μ-barb)<inf>2</inf>][Ag<inf>2</inf>(μ-en)<inf>2</inf>] · 5H<inf>2</inf>O}<inf>n</inf> (2) and [Ag(barb)(μ-bpe)]<inf>n</inf> (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)<inf>2</inf>] 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 {NaO<inf>6</inf>} 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. © 2006 Elsevier Ltd. All rights reserved.