Calculation of structural parameters in isostructural series: the kieserite group

In order to demonstrate the possibility of predicting the structural parameters of members in a sequence of isostructural compounds! the kieserite group isotypes (with the general formula (MXO4)-X-II.H2O) were chosen since a number of them have accurately refined crystal structures. The unit-cell parameters and the fractional atomic coordinates were shown to vary linearly with both cation and anion size. This makes it possible to calculate the structural parameters of a particular member, taking into account only the effective ionic radii of the constituent atoms. Agreement between the calculated and experimentally refined (by X-ray diffraction) structural parameters is good. The cell constants and atomic coordinates of FeSeO4.H2O, iron selenate monohydrate, are predicted in this way.