Regioselective reactivity, molecular cleft selectivity, and conformational properties have been examined in the skeletally stabilized triphosphazanes C6H4N2[P(NEt2)2]2PNEt2 (3), C6H4N2[P(S)(NEt2)2]2PNEt2 (4), C6H4N2[P(S)(NEt2)2]2PCl (5), and C6H4N2[P(S)(NEt2)2]2P(S)NEt2 (9) and in a series of new derivatives. 3 is oxidized/coordinated regioselectively by O3, Se, PhN3, and BH3 to C6H4N2[P(O)(NEt2)2]2PNEt2 (10) and C6H4N2[P(O)(NEt2)2]2P(O)NEt2 (11), C6H4N2[P(Se)(NEt2)2]2PNEt2 (12), C6H4N2[P(NPh)(NEt2)2]2PNEt2 (13), and C6H4N2[P(BH3)(NEt2)2]2PNEt2 (14), respectively. 4 reacts selectively with HBF4, CF3CO2H, and H3PO4 to form the endo-phosphorus-substituted C6H4N2[P(S)(NEt2)2]2PF (18), C6H4N2[P(S)(NEt2)2]2POC(O)CF3 (19), and C6H4N2[P(S)(NEt2)2]2POP(O)(OH)2 (20). Quantitative Mel quaternization or BH3 coordination of 4 yields {C6H4N2[P(S)(NEt2)2]2P(CH3)NEt2}I (16) or C6H4N2[P(S)(NEt2)2]2P(BH3)NEt2 (15). 5 reacts selectively with alcohols MeOH, EtOH, and i-PrOH (but is inert toward t-BuOH) to form C6H4N2[P(S)(NEt2)2]2POR [R = Me (21), Et(22), i-Pr (23)] and with BH3 to form C6H4N2[P(S)(NEt2)2]2PH (25) and its adduct C6H4N2[P(S)(NEt2)2]2PH(BH3) (24). New triphosphazanes 10-16 and 18-25 are characterized by spectral data. Structures of 9, 12, and 16 are determined by X-ray crystallography : 9, orthorhombic, Aba2, a = 23.111(4) angstrom, b = 21.324(5) angstrom, c = 14.609(3) angstrom, V = 7200(2) angstrom3, Z = 8, R=0.042, R(w) = 0.045; 12, orthorhombic, Pbca, a = 14.975(6) angstrom, b = 18.894(7) angstrom, c = 24.524(8) angstrom, V = 6939(3) angstrom3, Z = 8, R = 0.053, R(w) = 0.058; 16, orthorhombic, C222(1), a = 10.885(4) angstrom, b = 20.78(2) angstrom, c = 36.31(2) angstrom, V = 8214(9) angstrom3, Z = 8, R = 0.048, R(w) = 0.050. Variable-temperature P-31{H-1} NMR spectra of 3-5,10,11, 15,16, and 20 and of the known C6H4N2[P(S)(NEt2)2]2PNH2 (6), C6H4N2[P(S)(NEt2)2]2PN3 (7), and C6H4N2[P(S)(NEt2)2]2P(O)H (8) show that rotation around skeletal exo P-N bonds is unrestricted to below -90-degrees-C; only 9 and 11 freeze to unsymmetrical conformations at low temperatures.Rotation of the endo (CH3CH2)2N- group in the molecular cleft of 3 is unrestricted to -90-degrees-C; in 16 the group freezes to an unsymmetrical conformation below -40-degrees-C. Potential impacts of the observed reaction selectivity and conformational properties on oligomeric/polymeric phosphazane structure and reactivity are discussed.