originate from their small ionic radius. The ligand edtp is able apparently to fold itself almost optimally around the nickel and cobalt ions. With the larger metal ions (Fe, Mn, and Cd) six-coordinate octahedral coordination by the ligand edtp becomes too unfavorable, even when distorted, resulting in seven-coordinate "bicapped octahedral" geometries around the metal ions. The zinc compounds appear to be intermediate cases (see the coordination numbers in Table IV).Concluding Remarks. The pyrazole derivative of ethylenediamine, edtp, appears to be a hexadentate nitrogen donor ligand toward first-row transition-metal ions. Except for the small nickel(I1) ion the ligand edtp has a too restricted geometrical configuration to be able to form regular coordination octahedrons. Coordination numbers show a direct correlation with the ionic radii of the metal ions: The larger ions are seven-coordinate and the smaller ions are six-coordinate with Zn(I1) in an intermediate position.Acknowledgment. The authors are indebted to S . Gorter for the collection of the crystallographic data.Supplementary Material Available: Listings of bond lengths, bond angles, fractional coordinates of the hydrogen atoms, anisotropic thermal parameters of the non-hydrogen atoms, observed and calculated structure factors, and analytical data (13 pages). Ordering information is given on any current masthead page.Three compounds of empirical formula NbC14(PR3),, two of which (1 and 2) were previously reported and one of which (3) is new, have been structurally characterized. Compound 1, Nb2C18(PMe3),, is dinuclear, consisting of two squareantiprismatic NbC&(PMe3), units fused on a common square face formed by four C1 atoms. The molecule has crystallographic m m m (DZh) symmetry in the cubic space group Im3 with a = 16.372 [4] A and Z = 6. The Nb-Nb distance is 2.833 (1) A and the metal to ligand distances are Nb-Clb = 2.541 (1) A, N K I , = 2.502 (1) A, and Nb-P = 2.671 (1) A. Compound 2, rrans-NbCI,(PEt,),, forms monoclinic crystals (P2,/n) with unit cell dimensions of u = 7.224 (2) A, b = 12.131 (4) A, c = 12.017 (2) A, B = 90.74 (2)O, and 2 = 2. Compound 3, trans-NbCl,(PEtPh,),, also forms monoclinic crystals (P2Jn) with u = 9.851 (2) A, b = 16.010 (3) A, c = 9.367 (2) A, B = 98.67 ( 1 ) O , and 2 = 2. In both 2 and 3 there is crystallographic inversion symmetry imposed on the molecule, and the mean dimensions (for 2 and 3 in that order) are Nb-Cl = 2.366 [9], 2.367 [34] A and Nb-P = 2.664 (3), 2.706 (1) A. Observations on the colors, visible spectra, andEPR spectra of solutions of these compounds are reported and partially interpreted. Compound 1 and the previously reported NbzC18(PMe2Ph)4 exist in concentration-dependent equilibrium with EPR-active monomers, although the exact nature of the latter is uncertain.