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-3[Ag-3(mu-barb)(6)] (1), {[Ag-2(mu-barb)(2)][Ag-2(mu-en)(2)] center dot 5H(2)O}(n) (2) and [Ag(barb)(mu-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, H-1 NMR, DTA-TG and single-crystal X-ray diffraction. The structure of I 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(l) 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(l) is linearly coordinated by two N atoms of two barb ligands, while sodium(l) has a highly distorted {NaO6} coordination geometry by barb 0 atoms. The average Ag center dot center dot center dot Na separation of 3.5 8 (5) angstrom possibly indicates a kind of 'metallophilic' interaction between Ag and Na atoms. Complex 2 consists of I D anionic and cationic chains interconnected by way of Ag center dot center dot center dot 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 ID 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. (C) 2006 Elsevier Ltd. All rights reserved.