Several eighteen- and sixteen-electron derivatives of tungsten(0), molybdenum(0), and chromium(0) carbonyl complexes, including [PPN](2)[Cr(CO)(3)(O,S-C6H4)] (2c), [PPN](2)[W(CO)(3)(NH,S-C6H4)] (5c), [PPN](2)[W(CO)(3)(O,S-C6H4)] (6c), [PPN](2)[W(CO)(4)(S,S-C6H4)] (7b) have been synthesized from the reaction of photochemically generated M(CO)(5)THF with a series of doubly deprotonated 1,2-disubstituted benzene rings with the appropriate oxygen, nitrogen, and sulfur donor atoms. These complexes have been characterized in the solid state by X-ray crystallography and in solution by IR and C-13 NMR spectroscopies. The crystal of 2c (C84H71N3O5P4SCr) is triclinic P (1) over bar, a = 13.869(3) Angstrom, b = 23.128(5) Angstrom, c = 12.056(2) Angstrom, alpha = 104.84(3)degrees, beta = 106.91(3)degrees, gamma = 95.29(3)degrees, Z = 2; that of 5c (C89H77N7O3P4SW) is monoclinic P2(1), a = 11.054(2) Angstrom, b = 28.140(6) Angstrom, c = 12.556(2) Angstrom, beta = 90.58(1)degrees, Z = 2; that of 6c (C85H70N4O4P4SW) is triclinic P (1) over bar, 12.236(2) Angstrom, b = 14.419(2) Angstrom, c = 22.748(4)Angstrom, alpha = 76.44(1)degrees; beta = 75.98(2)degrees, gamma = 70.98(1)degrees, Z = 2; that of 7b (C82H64N2O4P4S2W) is triclinic P (1) over bar, a = 12.650(1) Angstrom, b = 14.810(1) Angstrom, c = 21.053(2) Angstrom, alpha = 77.182(7)degrees beta = 78.334(7)degrees, gamma = 66.579(7), Z = 2; and that of 8 (C10H8O4P2W) is monoclinic P2(1)/c, a = 11.582(1) Angstrom, b = 10.791(1) Angstrom, c = 10.449(1) Angstrom, beta = 100.867(7)degrees, Z = 2. The average nu(CO) frequencies for each tricarbonyl species reported are compared to those related dianions previously reported in order to gauge the pi-donor character of the different ligands. The C-13 NMR spectrum for each tricarbonyl derivative consists of a single sharp peak for the three inequivalent carbonyls as a result of a low-energy, fast intramolecular exchange process. Both inter-and intramolecular CO-exchange processes have been probed via variable temperature C-13 NMR. In the case of the 16-electron species the geometry of the metal dianion is that of a distorted trigonal bipyramid consisting of three carbonyl ligands and a five-membered chelate ring bound through the pi-donor atoms at an equatorial and an axial position, with the stronger pi-donor atom in the equatorial site. The equatorial site for the most effective pi-donor is preferred over the axial position because the unoccupied d(xy) orbital lies in the equatorial plane, and may be stabilized via a pi-donor ligand in the equatorial position. The axial position exhibits a filled/filled repulsion as both orbitals available for pi-bonding are filled.