Crystal structure of 6β-trimethylammoniopenicillanate hemihydriodide

Abstract

Crystals of the title compound are monoclinic, space group C2, with a= 19·44(3), b= 6·28(1), c= 11·33(2)Å, β= 95·0(1)°, Z= 4. The atomic co-ordinates were obtained from X-ray measurements by Fourier and least-squares calculations, the final value of R being 9·0% for 1380 visually estimated reflections. The carboxylate groups of two penicillanate groups are related by a short O(13)⋯ O(13^I) separation of 2·46(2)Å across a two-fold axis; this distance is typical of the short hydrogen-bonded separations in the acid salts of some carboxylic acids and the hemihydriodide is therefore formulated as [RCO₂⋯ H ⋯ O₂CR]⁺I^–. The β-lactam ring is puckered, with C(7) displaced by 0·31 Å from the plane defined by atoms C(5), N(4), and C(6). The thiazolidine ring approximates closely to an envelope form, with C(3) displaced by 0·47 Å from the mean plane through atoms C(2), S, C(5), and N(4).