The halo tricarbonyl complexes LWX(CO)(3) (X = I, Br, Cl) are formed when NEt4[LW(CO)(3)] is reacted with I-2, N-bromosuccinimide, and N-chlorosuccinimide (or PhICl2), respectively, while reaction of NEt4[(LW)-W-Pr(CO)(3)] and I-2 yields (LWI)-W-Pr(CO)(3) [L = hydrotris(3,5-dimethylpyrazol-1-yl)borate, L-Pr = hydrotris(3-isopropylpyrazol-1-yl)borate]. Reaction of Net(4)[LW(CO)(3)] with Br-2 yields mixtures of LWBr(CO)(3) and (LWBr)-W-Br(CO)(3) [L-Br = hydrotris(4-bromo-3,5-dimethylpyrazol-1-yl)borate] as a result of competitive bromination of both tungsten and ligand L. The complexes generally exhibit three nu(CO) bands, one at ca. 2025 cm(-1) and two between 1930 and 1900 cm(-1), and NMR spectra consistent with fluxional carbonyl-capped octahedral (C-s) structures. Crystals of (LWI)-W-Pr(CO)(3) . MeOH are orthorhombic, space group Pbca, with a = 11.779(2) Angstrom, b = 15.975(4) Angstrom, c = 29.476(3) Angstrom, and V = 5547(2) Angstrom(3) for Z = 8. The seven-coordinate complex exhibits a 3:3:1 carbonyl-capped octahedral structure. In hot acetonitrile or tetrahydrofuran, the tricarbonyl complexes are converted into brown, paramagnetic (mu(eff) ca. 1.15 mu(B)) dicarbonyl species, LWX(CO)(2) and (LWBr)-W-Br(CO)(2), which exhibit two nu(CO) bands (ca. 1930 and 1840 cm(-1)) and isotropically shifted NMR spectra consistent with a mononuclear structure with C-s symmetry. Further decarbonylation of (LWBr)-W-Br(CO)(2) in refluxing acetonitrile results in the formation of (LWBr)-W-Br(MeCN-kappa(2)-N,C-(CO), which crystallizes in monoclinic space group C2/c, with a = 22.245(4) Angstrom, b = 19.077(4) Angstrom, c = 15.639(3) Angstrom, beta = 128.61(2)degrees, and V = 5286(2) Angstrom(3) for Z = 8. The seven-coordinate complex features a "side-on" bonded, four-electron-donor acetonitrile ligand and a completely 4-brominated L-Br ligand.