Derivatives of benzo[b]furan. Part II. Structural studies of derivatives of 2- and 3-benzo[b]furancarboxylic acids

Abstract

The selected derivatives of the 2-and 3-benzo [b]furancarboxylic acids were synthesized and their structures were studied using the X-ray crystallography and the computational methods. The monocarboxylic acids (1-3) crystallize as dimers stabilized by the O-HÁÁÁO intermolecular hydrogen bonds. Moreover, intramolecular hydrogen bonds are formed between the OH and C(=O)CH 3 groups, substituted to the aromatic ring (2-4). In the crystal structures of 1-4, weak C-HÁÁÁO, C-HÁÁÁp, and C-HÁÁÁBr interactions stabilize the three-dimensional packing of molecules. The crystalline sodium complex of 1 has the stoichiometry [Na 1 Á1A 2 Á1B]Á1C, thus, the asymmetric unit contains three different moieties of 1. In this complex, the Na ? cation is hexacoordinated having a strongly distorted tetragonal bipyramidal polyhedron. For each molecule 1-4, several conformers were obtained in the gas phase. It was achieved by the rotations of substituents [COOR and/or C(=O)CH 3 , where R = H, CH 3 ] with respect to the rigid benzo[b]furan system. As indicated by the quantum-chemical calculations, the solid-state conformers for 3 and 4 (3-benzo[b]furancarboxylic acid derivatives) are the most stable ones. In contrast, the solidstate conformers of the 2-benzo[b]furancarboxylic acid derivatives (1, 2) have the energies higher than the lowest energy conformer by 1.23 and 0.69 kcal/mol, respectively. It seems that intermolecular contacts in the crystal influence on the orientation of substituents, and the conformers observed in the sodium complex of 1 provide evidence of such flexibility.

Synthesis, structure and bioactivity of a mononuclear octahedral [Prolinate2-Na(MeOH)4]−H+ complex

“…Although less common than transition metal complexes, sodium generates mononuclear complexes [11] with other ligands. [12] Searching in the literature, polymeric bis-tetrazole moieties generated octahedral hydrated sodium complexes,[13] DMF and water stabilized distorted octahedral sodium complex, [14] other sodium cation was surrounded by three units of 7-acetyl-2benzo[b]furancarboxylic acid, [15] and DMSO was a crucial ligand in the stabilization of the cluster [Na 4 (DMSO) 15 ] 4+ [(I 3 ) 3 (I)] based on octahedral metal cations. [16] To the best of our knowledge, a simple and mononuclear hexacoordinated sodium complex, partially complexed by alcohols are not frequently reported.…”