Crystal structures of the acid salts of some dibasic acids. Part VIII. An X-ray study of the β-form of rubidium hydrogen acetylenedicarboxylate, and a comparison with the isomorphous α-forms of the potassium and rubidium salts

Abstract

Rubidium hydrogen acetylenedicarboxylate, RbH(adc), in its α-form crystallises in the monoclinic system with a= 7·956, b= 12·307, c= 6·216 Å, β= 105·6°, Z= 4 in space group l2/a, and is isomorphous with the analogous potassium salt. In its β-form, RbH(adc) is triclinic with a= 6·344, b= 7·18, c= 7·92 Å, α= 96·9°, β= 106·1 Å, γ= 116·4°, Z= 2 in P. Thus the crystal symmetries of the α- and β-forms are quite different. The crystal structure of the β-form has been determined and refined from two independent sets of diffractometer data, to R 5·9%(530 terms) and 12·5%(1640 terms), which yield concordant positional parameters. Despite the difference of crystal symmetry the structures found for the hydrogen-anion and for the environment of the cation are very similar to those in the α-form. The hydrogen bond, unsymmetrical in the β-form, which links the anions into infinite chains has O ⋯ O 2·464(8)Å.

Cell data are also given for some other acid salts of H₂(adc).