Erratum to Kinetics of dehydration of single crystals of copper formate tetrahydrate by Fichte and Flanagan

Abstract

An error has been detected in the title paper [Fichte & Flanagan (1971). Trans. Faraday Soc. 67, 1467-1479] concerning the use of X-ray powder data to infer structural information. The nature of the error is discussed and the corrected information given. In the paper by Fichte & Flanagan (1971), the authors correctly ascribe the strong 6.23 A line in copper formate tetrahydrate (CFT) to (001)cvr, based on the well known argument that in lamellar structures strong, low-angle reflexions correspond to interplanar spacings between layers (Grim, 1953). Besides, the assignment was corroborated by single-crystal data, available at the time. After dehydration into copper formate anhydride (CFA), they assigned the strongest peak in the X-ray diagram (5.24A) to the corresponding (001)CFA , based on the same qualitative arguments. They thus inferred a 15.9% interplanar contraction in good agreement with the 16.0% they measured in the bulk. As no single-crystal work was attempted at the time, this was as far as they could go. Recently, a thorough crystallographic report has appeared (Gfinter, 1980) on the topotactically dehydrated pseudomorph CFA. The powder data presented therein show 0108-2701/84/071299-01501.50 that the strong 5.24 A line in fact corresponds to (110)CFA , (001)cr A being 3.06 A and with only a medium intensity. The collapse of (001)cv r planes is thus much more severe (51% shrinkage) than reported by Fichte & Flanagan. Measured values in the bulk, however, are usually very low, due perhaps to some splitting taking place at a submicroscopic level along CFT cleavage planes. Figures as low as a few per cent are not uncommon, even under very careful working conditions. It was certainly an unfortunate coincidence, then, for the authors to have such a misleading match between their measured and expected values. The reason why a well established, general rule failed to provide the right answer should be attributed to the fact that it was applied too loosely: although CFT is a perfectly suitable (as far as the rule is concerned) layered structure, CFA is not, being distinctly three dimensional in nature. The rule, then, was not applicable from the onset.