THE STRUCTURE OF POTASSIUM HYDROGENTARTRATE - A COMBINED X-RAY, SEMIEMPIRICAL, AND AB-INITIO STUDY

Single crystals of potassium hydrogen ate, (2R, 2R)-KO2C(CHOH)(2)CO2H, were taken from a three-year-old wine bottle. The structure was deter mined by low-temperature single-crystal X-ray diffraction analysis usi ng a Siemens SMART diffractometer. (2R, 2R)-KO2C(CHOH)(2)CO2H crystall izes in the orthorhombic space group P2(1)2(1)2(1) with Z = 4 and unit cell dimensions a = 7.6065(5), b = 7.7599(5), and c = 10.6054(7) Angs trom. The structure of an isolated hydrogentartrate anion, (2R, 2R)-[O 2C(CHOH)(2)CO2H](-), was calculated at the semiempirical AM1 and PM3 l evels of theory with a VSTO-3G basis set and in addition ab initio at the self-consistent level of theory using a standard 6-31G(d,p) basis set (Non-SI units employed: kcal approximate to 4.184 kJ, Angstrom = 10(-10) m). (C) 1998 John Wiley & Sons, Inc.