A silicophosphonate bearing four hydroxyl groups, [RSi(OH){OP(O)(H)(OH)}] 2O (2; R = (2,6- iPr 2C 6H 3)N(SiMe 3)), has been isolated from the reaction between RSi(OH) 3 and [EtNPCI] 3. In contrast, the reaction between the sodium salt of substituted phenols and [EtNPCI] 3 yields [EtNP(OAr)] 3 [Ar = -C 6H 3 iPr 2-2,6 (3), -C 6H 2Me 3-2,4,6 (4), -C 6H 3Me 2-2,6 (5), -C 10H 7-1 (6), and -C 6H 4 tBu-4 (7)]. The cis isomers 3a-7a preferentially crystallize out from the cis/trans isomeric mixture. Single-crystal X-ray diffraction studies carried out for 3a, 4a, and 5a reveal that the P 3N 3 ring adopts a flattened-chair conformation with the aryloxy substituent on all three phosphorus atoms occupying the axial position. Oxidation of the cis isomers 3 and 5 by H 2O 2, sulfur, and selenium yields the trichalcogenides [EtNP(E)(OC 6H 3 iPr 2-2,6)] 3 (E = O (8), S (10), Se (12)) and [EtNP(E)(OC 6H 3Me 2-2,6)] 3 (E = O (9), S (11), Se (13)). The reaction leading to the formation of the triselenide 12 also produces small quantities of the diselenide [Et 3N 3P 3(OR) 3Se 2] (R = -C 6H 3 iPr 2-2,6) (14). The P 3N 3 ring in these λ 5-phosphazanes is highly distorted and resembles more of a twist-boat conformation. The DFT calculations on model systems [HNP(S)(OMe)] 3 (15) and [HNP(Se)(OMe)] 3 (16) indicate five low-lying unique conformers A-E. The chair conformer with a triaxial-OMe group is identified as the lowest-energy conformer in both cases. © 2009 American Chemical Society.