Dicarbonylbis(triphenylphosphine)cobalt hydride [HCo(CO)(2)(PPh(3))(2)] (1) has been prepared from the reaction of HCo(CO)(4) with PPh(3). Recrystallization of the isolated product from acetonitrile led to yellow crystals suitable for X-ray diffraction. The structures of both a trigonal bipyramidal (TBP) form and a square-pyramidal (SP) form of 1 were determined by X-ray diffraction from two crystals grown in the same crystallization. 1(TBP) crystallizes in the triclinic space group P ($) over bar 1, with a = 10.608(2) Angstrom, b = 12.543(2) Angstrom, c = 13.029(2) Angstrom, alpha = 65.67(2)degrees, beta = 82.31(2)degrees, gamma = 82.37(2)degrees, V = 1559.6(5) Angstrom(3), and Z = 2 at T = 123(5) K, with final residuals of R(F) = 0.039, R(W)(F) = 0.046, and S(F) = 1.25 for 5645 observed reflections and 391 parameters. 1(SP) crystallizes in the triclinic space group P ($) over bar 1, with a = 8.956(2) Angstrom, b = 12.558(3) Angstrom, c = 16.862(5) Angstrom, alpha = 98.99(2)degrees, beta = 93.64(2)degrees, gamma = 111.50(2)degrees, V = 1590.1(7) Angstrom(3), and Z = 2 at T = 123(5) K, with final residuals of R(F) = 0.039, R(W)(F) = 0.042, and S(F) = 1.60 for 5958 observed reflections and 353 parameters. These are the first crystal structures of a mononuclear hydridodicarbonylbis(phosphine)cobalt complex to be reported. Moreover, this is the first report that we are aware of in which two allogons of a neutral five coordinate metal complex have been structurally characterized. The TBP form has the hydride ligand in an axial position, trans to a carbonyl ligand. This geometry is similar to those reported in all previous structures of HCo(L)(n)(PR(3))(4-n) complexes (n = 0-4, n not equal 2). The more unusual SP form has a carbonyl ligand [C(1)-O(1)] in the axial position. This structure exhibits disorder of the phenyl rings of one phosphine ligand, although generally the molecular geometry is quite precisely defined. The Co-H distances of 1.37(3) and 1.45(4) Angstrom, for the TBP and SP forms, respectively, are comparable to those determined in other cobalt hydride structures.