Synthesis and characterization of monomeric and dimeric manganese(II) and zinc(II) complexes of pyridine-2-carbaldoxime

Abstract

The syntheses and characterization of two complexes of manganese(II) and one complex of zinc(II) with the ligand pyridine-2-carbaldoxime, C6H6N2O, are described. The monomeric manganese(II) complex cis-[Mn(C6H6N2O)2Cl2] (1) crystallizes in the orthorhombic space group Pbcn with 4 formula units in a cell of dimensions a = 12.479(3) Å, b = 10.348(2) Å, and c = 11. 974(2) Å. The structure has been refined to a final value of the conventional R-factor of 0.0330 based on 1513 observed independent reflections. The analogous zinc(II) complex, cis-[Zn(C6H6N2O)2Cl2] (2) also crystallizes in the orthorhombic space group Pbcn with 4 formula units in a cell of dimensions a = 12.215(2) Å, b = 10.383(2) Å, and c = 12. 016(2) Å. The structure has been refined to a final value of the conventional R-factor of 0.0377 based on 1117 observed independent reflections. The two complexes are isostructural, with the central metal atom lying on a crystallographic 2-fold axis. Both complexes are approximately octahedral, the coordination being provided by two trans pyridine nitrogen atoms and two cis amine nitrogen atoms from the oxime ligands, and by two cis chlorides. The dimeric manganese(II) complex [(C6H6N2O)(CH3OH)ClMnCl2MnCl(CH3OH)(C6H6N2O)] (3) crystallizes in the monoclinic space group P21/n with 2 formula units in a cell of dimensions a = 7.895(2) Å, b = 11.196(3) Å, and c = 12. 544(2) Å, and b = 98.39(2)o. The structure has been refined to a final value of the conventional R-factor of 0.0312 based on 1568 observed independent reflections. There is a crystallographic inversion center in the middle of the dimer relating one manganese center to the other. The geometry at each manganese(II) center is again roughly octahedral, coordination being provided by two nitrogen atoms from the oxime ligand, a terminal chloride ion trans to the amine nitrogen, the oxygen atom of the coordinated methanol molecule, and two bridging chlorides that link the two halves of the dimer. The Mn$$$Mn separation is 3.647(1) Å and the bridging Mn-Cl-Mn angle is 91.8(1)o. The temperature dependence of the magnetic susceptibility of 3 exhibits a maximum at approximately 8 K, indicative of a weak antiferromagnetic interaction between the two metal centers with J = 1.94(1) cm-1. The EPR spectrum of 1 diluted into the corresponding Zn(II) host has been fitted to the parameters g = 2.00, A = 0.0084 cm-1, D = 0.157 cm-1, and E = 0.0005 cm-1. The small value of E/D is consistent with the observed symmetry of the complex. (Received January 19, 2000; revised July 6, 2000)Bull. Chem. Soc. Ethiop. 2000, 14(2), 128-142Bulletin of the Chemical Society of Ethiopia. ISSN: 1011-3924