The potentially bidentate hybrid ligand (o-hydroxyphenyl)diphenylphosphine, abbreviated POH, reacted via ligand-exchange with pentavalent rhenium precursors to give a series of six-coordinate mono- and dioxo complexes. Accurate control of the metal:ligand stoichiometric ratio allowed for the isolation of the mono-substituted [ReOCl3(PO)](-) (1) and [ReOCl2(PO)(PPh(3))] (2) derivatives. 1 was found to be the key intermediate for the syntheses of three more types of bis-substituted compounds : anionic dioxo [ReO2(PO)(2)][A] (A = NBu(4) (3), AsPh(4) (4)), neutral monooxo [ReOX(PO)(2)] (X = Cl (5), Br (6), I (7)), and neutral monooxo mixed-ligand [ReOX(PO)(PNH)] [PNH = (o-amidophenyl)diphenylphosphine; X = Cl (8), Br (9), I (10)] complexes. In the monosubstituted complexes, the P,O-donors of the bidentate ligand spanned an equatorial (P) and the apical position (O) trans to the Re=O linkage in a distorted octahedral arrangement.In all of the bis-substituted monooxo compounds, the second chelate ligated on the equatorial plane almost orthogonally positioned with respect to the first one, the two phosphorus donors showing a mutual cis-(P,P) orientation. Dioxo complexes retained the cis(P,P) configuration with the bidentate ligands symmetrically coordinated on the equatorial plane normal to the trans-ReO2 core. All the complexes were characterized by various physical techniques, including IR, MS, and H-1/P-31{H-1} NMR. The X-ray structure of a representative compound for each category, namely [ReOCl3(PO)][NBu(4)] (1), [ReO2(PO)(2)][AsPh(4)] (4), [ReOCl(PO)(2)] (5), and [ReOCl(PO)(PNH)] (8), were determined. Crystals of 1 were monoclinic, P2(1)/n, a = 10.840(3) Angstrom, b = 22.167(6) Angstrom, c = 15.210(4) Angstrom, beta = 95.91(2)degrees, and Z = 4; those of 4 were triclinic, P (1) over bar, a = 12.679(7) Angstrom, b = 13.082(7) Angstrom, c = 19.649(8) Angstrom, alpha = 82.64(4) Angstrom, beta = 81.16(4)degrees, gamma = 62.27(3)degrees, and Z = 2; those of 5 were orthorhombic, a = 10.225(4) Angstrom, b = 14.208(6) Angstrom, c = 21.771(9) Angstrom, P2(1)2(1)2(1), and Z = 4; and those of 8 were orthorhombic, a = 10.199(2) Angstrom, b = 14.147(4) Angstrom, c = 21.772(6) Angstrom, P2(1)2(1)2(1), and Z = 4. The four structures were solved by the Patterson method and refined by full-matrix least-squares procedures to R = 0.050, 0.063, 0.043, and 0.039 for 1, 4, 5 and 8, respectively. Both solution state (P-31{H-1} NMR) and solid state (X-ray) demonstrated a cis-(P,P) arrangement for each bis-substituted complex, with the Re atom at the center of a highly distorted octahedron. Detailed analyses of the IR spectra of this series of Re(V) compounds in the region 900-580 cm(-1) allowed us the possibility to distinguish between symmetrical and asymmetrical bis-substituted complexes.