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CTURE OF ORGANIC COMPOUNDS Dedicated to the memory of N.V. Belov

Crystal Structure of Potassium Sodium Tartrate Trihydrate A. E. Egorova, V. A. Ivanov, N. V. Somov, V. N. Portnov, and E. V. Chuprunov Lobachevsky State University of Nizhni Novgorod, pr. Gagarina 23, Nizhni Novgorod, 603950 Russia email: ae[email protected] Received April 13, 2010; in final form, March 22, 2011

Abstract—Crystals of potassium sodium tartrate trihydrate (dlKNaC4H4O6 · 3H2O) were obtained from an aqueous solution. The crystal shape was described. The atomic structure of the compound was determined and compared with the known structures of dlKNaC4H4O6 · 4H2O and lKNaC4H4O6 · 4H2O. DOI: 10.1134/S1063774511060071

INTRODUCTION Tartrate crystals are widely used in science, engi neering, medicine, food industry, etc. Investigations of their mechanical, thermodynamic, electrical, nonlin ear optical, and physical properties are presently underway [1–3]. The physical properties of crystals of potassium sodium tartrate are still of interest for researchers. The optical properties of the ferroelectric salt (lKNaC4H4O6 · 4H2O) were studied in [4]. The relax ation behavior of the domain structure of this crystal during repolarization by a static electric field was investigated in a wide temperature range [5]. The dielectric and pyroelectric properties of nanocompos ites with inclusions of lKNaC4H4O6 · 4H2O were reported in [6]. Experiments on improving the proce dure for singlecrystal growth were performed [7], and the influence of impurities on the facegrowth rate was investigated [8, 9]. Tartrate molecules can adopt the following three stereochemical configurations: lefthanded, right handed, and meso. Depending on the presence and ratio of different molecular configurations in solution, crystals of ltartrates, dtartrates, dltartrates, or mesotartrates precipitate. Crystals containing differ ent amounts of water of crystallization can form dur ing crystallization. Hence, it is of interest to investigate different crys tallization forms of tartrates. In the present study, sin gle crystals of potassium sodium tartrate trihydrate dl KNaC4H4O6 · 3H2O (I) were obtained and character ized for the first time and the crystal structure was determined.

of I precipitated overnight, followed by the formation of the crystals of dlKNaC4H4O6 · 4H2O (II). The probability of crystal formation of the trihydrate is substantially higher if a seed is introduced into a solu tion of dlKNaC4H4O6. Thus, crystals of I with a lin ear size of approximately 1.5–2 cm grew approxi mately overnight. The seeding made it possible to obtain larger crystals suitable for investigations into their physical properties. Since it was impossible to reliably determine the type of the resulting crystals based on their external shape and other visual features, the samples were iden tified by Xray diffraction. METHODS OF INVESTIGATION The measurements for crystals of I were carried out on a crystal with a linear size of 2 cm using a contact goniometer with an