Structural and spectroscopic studies of Na+ – Quercetin-5′-sulfonic acid polymeric complexes obtained via solvothermal synthesis

Abstract

New sodium complexes of quercetin-5′-sulfonic acid (HQSA) have been obtained. The aqua complex of the general formula [NaQSA∙(H2O)2]·2H2O (1) was a starting compound for solvothermal syntheses of acetone and dimethylsulfoxide (S) complexes: [NaQSA(S)](S) (2 – acetone) and [NaQSA(S)]∙2(S) (3a and 3b – DMSO). The fourth complex obtained from the reaction of HQSA excess used in the reaction with NaOH is [Na(QSA)2·2H2O][(EtOH)2H] (4). The molecular and crystal structures of 1 – 4 were determined by X-ray crystallography. The sodium cations are coordinated by six or seven oxygen atoms; Na+ coordinating groups are sulfonic, hydroxyl, and carbonyl of the QSA− anion. The bridging role of some functional groups causes the formation of polymeric complexes. The coordination spheres are completed by oxygen atoms from the coordinating water (in 1 and 4), acetone (2) or DMSO molecule (3a and 3b). In each structure non-coordinating interstitial solvate molecules are also present; they are two H2O (1), acetone (2), two DMSO (3a and 3b), and the hydrogen bisethanol cation [EtOH…H+…EtOH] (4). The last of these is a rare type of Zundel type cation. Unstable complexes (2 and 3), that decompose under normal conditions, are formed and they have a structure of intercalation clathrates. The solvating molecules, located between 1D or 2D polymeric complexes, play a unique role as a network bonding agent. Theoretical calculations showed charge separation between Na+ and SO3−. The FTIR and Raman spectra are consistent with the solved crystal structures and, importantly, enable the identification of acetone and DMSO molecules in the powder samples.