Abstract We have studied the controlled hydrolysis of P3N3Cl6 (A) under basic conditions (Et3N/H2O in CDCl3) by 31P n.m.r. Our results are in some respects at variance with those reported in acid conditions by Gabler and Haw1, but agree better with results of van de Grampel et al.2,3 The first species observed (I) we assign structure B, and our data agree well with those of van de Grampel et al2, who isolated salts containing the anion. Gabler and Haw1 quote a higher coupling constant and a higher shift for the PClO phosphorus, but this can be explained by the more acid conditions they used. Species such as B exist as an equilibrium of anionic and tautomeric O- and N-protonated structures. Further hydrolysis gives rise to four more species, two A2X systems, II and III, and two P-O-P bridged species, one symmetrical [A2X]2 system IV, and one asymmetrical A2XYB2 system V. The symmetrical system IV, whose second order spectrum clearly shows the effect of the P-O-P coupling, cannot be C, for which an X-ray cr...