The structure of (−)D-[Co(tn)3]Br3·H2O (tn: H2N–CH2-CH2-CH2-NH2) has been solved by the heavy atom method and refined to R=0.11 by least-squares analysis based on 1845 threedimensional data. The substance crystallizes in the monoclinic space group P21 with unit cell dimensions: a=16.274, b=9.863, c=9.489 Å, β=126.4° and Z=2. The complex ion in the structure has approximately a three-fold axis of rotation. The three six-membered Co-tn rings are nearly identical and take chair form. The chelate ring is rather flattened out, owing to the strong H-H repulsion. The absolute configuration of (−)D-[Co(tn)3]3+ has been found to be the same as that of (+)D-[Co(en)3]3+.
The Crystal Structure of [Ni(H2O) The crystal structure of trans-diaquo-bis(pyridine-2-carboxamide)nickel(II) chloride, [Ni-(H2O)2(piaH)2]Cl2, was determined by X-ray diffraction and refined by three-dimensional leastbuilt up of centrosymmetric complex ions and chloride ions. Two ligand molecules are coordinated to the nickel atom in trans position with amide oxygen atoms and ring nitrogen atoms. (Ni-N, 2.02 A, Ni-O, 2.05 A). The ligand molecules are nearly planar and they are approximately in one plane with the nickel atom. Two water molecules are coordinated at a distance of 2.14A and complete the octahedral arrangement around the nickel atom.Metal chelates of pyridine-2-carboxamide, picolinic acid amide, have scarcely been studied. Recently copper and nickel chelates were synthesized and their physical properties were studied.1) In the following, the ligand, pyridine-2-carboxamide, C5H4NCONH2 is abbreviated as piaH. The nickel(II) chelates prepared were a. Ni(pia)2.2H2O and b. Ni(piaH)2Cl2.2H2O. Substance a is fine orange-red crystals and diamagnetic, while b is blue needles and paramagnetic with the magnetic moment 3.25 B. M. From the measurements of absorption spectra and magnetic moments, it has almost been established that the coordination around the nickel atom in substance a is square planar and that in b is octahedral. Pyridine-2-carboxamide may be coordinated as bidentate ligands in two ways, namely by means of two nitrogen atoms (I) or one nitrogen and one oxygen atom (II), since the rotation around the C-N bond is possible. To decide between these two possibilities and to establish the conformation of the chelate ring, the crystals were subjected to X-ray crystal analysis. In this paper the crystal structure of the substance b will be reported.
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