Dipotassium dialuminium cyclo­octa­phosphate

Single crystals of the title compound, K(2)Al(2)P(8)O(24), were obtained by solid-state reaction. The monoclinic structure is isotypic with that of the Ga(III) analogue and is built of eight-membered phosphate ring anions P(8)O(24) (8−) (2/m symmetry) isolated from each other and further linked by isolated AlO(6) octa­hedra ([Image: see text] symmetry) by sharing corners. Each AlO(6) octa­hedron is linked to four P(8)O(24) (8−) rings in such a way that two rings are linked through bidentate diphosphate groups attached in the cis positions on two opposite parallel edges of the octa­hedron. The two other rings are linked via corner-sharing to the two remaining corners in the trans positions of the AlO(6) octa­hedron. Each P(8)O(24) (8−) ring anion is linked to eight AlO(6) octa­hedra. More accurately, each ring anion is linked to four AlO(6) octa­hedra through bidentate diphosphate groups attached in the cis positions to the AlO(6) octa­hedron and to the four remaining octa­hedra by sharing corners. This three-dimensional linkage delimits channels running parallel to [001] in which the ten-coordinated K(+) cations (2 symmetry) are distributed over two columns. These columns alternate with empty octa­gonally-shaped channels expanding through the P(8)O(24) (8−) ring anions.