Synthetic products of the form M1−xAlx(OH)2Rx/n−n·yH2O with M = Mg, Ni and R = CO3 and/or ClO4 have been prepared, with x ranging from about 0.33 to 0.20, by precipitation from mixed perchlorate solutions by addition of NaOH; the carbonate ion is present owing to solution of atmospheric CO2. The two kinds of anions show a strong tendency to segregate into separate crystals or, under particular conditions, into separate layers within the same crystals, forming an alternating sequence of carbonate and perchlorate layers. Pure carbonate and pure perchlorate phases were obtained by anion exchange reactions. The parameter c', layer thickness, diminished with increase in Al3+ ions due to increase in electrostatic attraction between positive layers and negative interlayers. The parameter a for a hexagonal cell also diminished with increase of Al3+ ions because of their smaller size. The observed change Δa/Δx agrees semi-quantitatively with calculated values. Reasons are suggested for the range of Al3+ ions which can substitute in mixed hydroxide phases and for the commonly observed value of x ⋍ 0.25 in natural minerals, based on possible supercell arrangements of the Al3+ and M2+ ions.

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