The crystal structures of the acid salts of some monobasic acids. Part XII. Potassium hydrogen diaspirinate [bisacetylsalicylate]

Abstract

The crystal structure of potassium hydrogen diaspirinate [bisacetylsalicylate], KH[C₆H₄(OCOCH₃)CO₂]₂, has been determined by X-ray analysis. The monoclinic cell, comprising 4 molecules, has a= 26·63, b= 7·207, c= 10·68 Å, β= 116·24° and belongs to the space-group C2/c. The structure, which is isomorphous with that of the acid rubidium salt described in the preceding Paper, has been refined by anisotropic least-squares analysis to an R-value of 9·9% for 2731 reflexions. Each potassium ion lies on a two-fold axis and makes contact with an oxygen atom from each of six different aspirinate residues, and each aspirinate makes contact with three different potassium ions. The acidic hydrogen atom is involved in a very short hydrogen bond, with O⋯O = 2·455 ± 0·005 Å, which connects two aspirinate residues across a centre of symmetry. The significance of such (apparently) symmetrical O⋯H⋯O bonds is discussed. The dimensions of the aspirinate residue agree well with those found in the rubidium isomorph; they are compared with corresponding dimensions of the molecules of aspirin and of salicylic acid.