Skeletal P-N-P unit conformational preferences of the unsymmetrically substituted bis(phosphino)amines erythro-i-PrN[PhP(i-PrNH)][PhP(EtNH)] (4A), meso- and d,l-i-PrN[PhP(i-PrNH)]2 (5A and 5B), erythro-i-PrN[PhP(i-PrNH)][PhP(t-BuNH)] (6), erythro-i-PrN[PhP(i-PrNH)][PhP(PhNH)] (7), and erythro-i-PrN[PhP-(PhNH)]2 (8) have been examined. Compound 8, newly prepared in this study, and the previously synthesized 4A and 5A have been characterized by X-ray single-crystal analysis : 4A, monoclinic, P2(1)/n, a = 10.678(4) angstrom, b = 16.159(12) angstrom, c = 13.291 (4) angstrom, beta = 107.839(26)-degrees, V = 2183(2) angstrom3, Z = 4, R = 0.0602, R(w) = 0.0898; 5A, orthorhombic, Pbca, a = 10.616(5) angstrom, b = 16.340(7) angstrom, c = 26.81(2) angstrom, V = 4651(4) angstrom3, Z = 8, R = 0.0623, R(w) = 0.0724; 8, triclinic, P1BAR, a = 10.226(5) angstrom, b = 10.793(4) angstrom, c = 13.370(6) angstrom, alpha = 69.17(3)degrees, beta = 71.13(4)degrees, gamma = 68.86(3)degrees, V = 1253.8(10) angstrom3, Z = 2, R = 0.0602, R(w) = 0.0784. Compounds 4A, 5A, and 8, like the previously characterized 6, all assume a conformation around the P-N-P skeleton in which the assumed lone-pair electron positions are approximately trans and parallel to the P2N molecular plane. P-31 NMR spectra of the 4A, 5A, 6,7, 8, and 5A/5B mixtures in solution as a function of temperature show that the bis(phosphino)amines exist as an average of exchanging conformations at 25-degrees-C, but at low temperatures they freeze into preferred conformations. 5A, 5B, 6, and 8 show one conformation at low temperature; 4A and 7 exist as mixtures of two conformers. Analysis of 2J(PNP) skeletal P-N-P coupling constants shows that the preferred, lowest energy, conformation is approximately the same as seen in the solid state.