The reactions of the cyclic thionylphosphazenes [NSOX(NPCl2)(2)] (1, X = Cl; 2, X = F) with three oxygen-based nucleophiles of increasing basicity, sodium phenoxide (NaOPh), sodium trifluoroethoxide (NaOCH2CF3), and sodium butoxide (NaOBu) have been studied. The reaction of 1 and 2 with 4 equiv of NaOPh at 25 degrees C yielded the regioselectively tetrasubstituted species [NSOX{NP(OPh)(2)}2] (5d, X = Cl; 6d, X = F). Further reaction of 5d with an additional 2 equiv of NaOPh over several days or at elevated temperatures gave the fully substituted compound [NSO(OPh){NP(OPh)(2)}2] (5e), whereas 6d did not react further. The reaction of 1 and 2 with 5 equiv of NaOCH2CF3 yielded in both cases [NSO(OCH2CF3){NP(OCH2CF3)(2)}(2)] (7e), and similarly reaction with 5 equiv of NaOBu yielded [NSO(OBu){NP(OBu)(2)}(2)] (9e). In all cases, the reactions were monitored by P-31 NMR and (where applicable) F-19 NMR and were found to involve complete substitution at phosphorus via a predominantly vicinal pathway, followed by substitution at sulfur. Substitutional control of the reactions of NaOPh, NaOBu, with 1 and 2 was found to conform to the following general order of reactivity, PCl2 > PCl(OR) > SOX )X = Cl, F). Although the reaction with NaOCH2CF3 followed the same order of reactivity, a significant enhancement of reaction rate was detected with each equivalent of trifluoroethoxide added, Reaction of 7e with excess NaOCH2CF3 led to elimination of (CF3CH2)(2)O and the formation of the salts Na[NSO(OCH2CF3>NP(OCH2CF3)(2)NP(OCH2CF3)0] (11) and Na[NS(O)O{NP(OCH2CF3)2}(2)] (12). Crystals of 6d are triclinic, space group P (1) over bar, with a = 9.789(3) Angstrom, b = 11.393(4) Angstrom, c 12.079(5) Angstrom, alpha 107.40(3)degrees, beta = 91.23(3)degrees, gamma = 93.18(3), V = 1283.6(8) Angstrom(3), and Z = 2. Crystals of 5e are monoclinic, space group C2/c, with a 32.457(3) Angstrom, b = 10.747(1) Angstrom, c 18.294(2) Angstrom, beta 110.37(1)degrees, V = 5982.4(9) Angstrom(3), and Z = 8.