CALCULATION OF STRUCTURAL PARAMETERS IN ISOSTRUCTURAL SERIES - THE KIESERITE GROUP

In order to demonstrate the possibility of predicting the structural p arameters of members in a sequence of isostructural compounds! the kie serite group isotypes (with the general formula (MXO4)-X-II.H2O) were chosen since a number of them have accurately refined crystal structur es. The unit-cell parameters and the fractional atomic coordinates wer e shown to vary linearly with both cation and anion size. This makes i t possible to calculate the structural parameters of a particular memb er, taking into account only the effective ionic radii of the constitu ent atoms. Agreement between the calculated and experimentally refined (by X-ray diffraction) structural parameters is good. The cell consta nts and atomic coordinates of FeSeO4.H2O, iron selenate monohydrate, a re predicted in this way.