The Crystal Structure of trans-Diaquo-bis(pyridine-2-carboxamide)-nickel(II) Chloride, [Ni(H2O)2(piaH)2]Cl2

Abstract

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.

The crystal structure of bis(pyrazine-2-carboxamide)copper(II) perchlorate

“…In the course of studies on the bivalent metal complexes of acid amides, X-ray crystal analyses of [Ni(pia)2]2H20 (Nawata, Iwasaki & Saito, 1967), [Ni(H20)2(piaH)2]CI2 (Masuko, Nomura & Saito, 1967), [Cu(H20)2(piaH)2]Cl2 (Brown, MacSween, Mercer & Sharp, 1971) and [Cu(CIO4)2(paaH)2] (Sekizaki, Marumo, Yamasaki & Saito, 1971) have revealed that the first complex has a structure with square-planar coordination through the amide nitrogen and ring nitrogen atoms of the ligand, while the remaining three have a structure with octahedral or distorted octahedral coordination through the amide oxygen and ring nitrogen atoms where piaH and paaH denote pyridine-2-carboxamide and pyridine-2-acetamide respectively.…”