Abstraet. Sb2(HPO3)3, Pi, a= 9.182 (1), b= 8.353(1), c=7.220(1)A, , =68.21(1), ~= 79.52(1), y=66.47(1) ° at 297 K, Z=2, D o= 3.33 (4) at 296 K, D c = 3.41 Mg m -3. R = 0.020 for 2150 reflexions. The structure consists of isolated HPO 3 tetrahedra and Sb atoms coordinated to four O atoms.Introduction. The title compound was studied as part of an investigation of phosphites. Reaction of antimony trioxide with a concentrated aqueous solution of phosphorous acid (3.5 mmol Sb20 3, 30-150 mmol H3PO 3, and water to 15 ml) gave a voluminous precipitate from which, after standing for more than one year at 298 K, brownish crystals of the title compound were obtained (Vojti~ek, 1979), with well developed faces { 100} and {011 } of maximum prism dimensions 0.3 x 0.3 x 0.5 mm. 4428 intensities were collected (co/20 scan) in the range 3 _< 20 _< 55 ° from a crystal of volume 0.0157 mm 3 on a Stoe four-circle diffractometer with graphite-monochromated Mo Ka radiation (2 = 0.71069A). 2163 reflexions were unique; those with F < 2a(F) were treated as unobserved. The remaining 2150 reflexions were corrected for Lp and absorption effects (/~ = 6.24 mm-~).The