The complexes Mo-2(OAc)Cl-3(eta(3)-tetraphos-2) (tetraphos-2 = P(CH(2)CH(2)PPh(2))(3), 1, and Mo-2(OAc)Cl-3(eta(3)-etp) (etp = Ph(2)PCH(2)CH(2)P(Ph)CH(2)CH(2)PPh(2)), 2, were prepared by reactions of Mo-2(OAc)(2)Cl-2(PPh(3))(2) with tetraphos-2 and etp, respectively, in CH2Cl2. Their UV-vis and P-31-NMR spectra have been recorded and their structures have been determined, Crystal data for 1 : space group Pbca, a = 24.450 (2) Angstrom, b = 27.486 (3) Angstrom, c = 15.017 (3) Angstrom, V = 10091 (2) Angstrom(3), and Z = 8, with final residuals R = 0.0683 and R(w) = 0.0724. Both the tetraphos-2 and etp ligands coordinate to the Mo centers in tridentate fashions with chelating/bridging bonding modes. The complexes that are also bridged by the acetate ligands are twisted about the metal-metal bonds with average twist angles of 13.2 degrees for 1 and 11.4 degrees for 2, respectively, The lowest energy bands at 643 nm (14 389 cm(-1), epsilon = 909 M(-1) cm(-1)) for 1 and 644 nm (14388 cm(-1), epsilon = 1536 M(-1) cm(-1)) for 2 can be assigned to delta --> delta* transitions, The study on P-31{1H} NMR spectra of 1 and 2 concluded that the through metal-metal quadruple bonding coupling (3)J(P-Mo-Mo-P) is about 20 +/- 1 Hz.