Nickel(II) N2O2 Schiff-base complexes incorporating pyrazole: Syntheses, characterization and acidity of the metal centre towards co-ordinating solvents (original) (raw)
Related papers
Two new bidentate imidazolylphosphine P–N chelate ligands 2-(diphenylphosphinomethyl)-1-methylimidazole (PN I) and 2-(diisopropylphosphinomethyl)-1-methylimidazole (PN II) have been synthesized in good yields by treating R 2 PCl (R = Ph or Pr i) with 1-methyl-2-trimethylsilylmethylimidazole. Various types of nickel(), cobalt-() and-() complexes have been prepared with these two ligands and characterized by physico-chemical techniques. The structures of PN I HBr and two nickel() complexes, [Ni(PN I) 2 ][BF 4 ] 2 2 and [Ni(PN II) 2 ][BF 4 ] 2 MeCN 4MeCN, have been studied by single crystal X-ray analyses. Both take planar structures with different configurations. In 2 the two phosphorus atoms are in cis position whereas in 4MeCN they are trans to each other. The complex [NiCl 2 (PN I)] 1 adopts a five-coordinate dimeric structure with chloride bridges in the solid state and a monomeric square-planar structure, [Ni(PN I)(solv) 2 ]Cl 2 , in aqueous and in methanolic solutions. However, complex [NiCl 2 (PN II)] 3 is diamagnetic and takes square-planar geometry around the metal ions both in the solid and solution states. The structures of cobalt(), [CoX 2 (L)] (where X = Cl or Br), and cobalt() complexes, [Co(acac) 2 (L)]ClO 4 (where acac = acetylacetonate, L = PN I or PN II), are tetrahedral and octahedral, respectively. A variable temperature 1 H and 31 P NMR study of complexes 1 and 2 demonstrated the presence of dynamic motion of the PN-chelate ring(s). On the other hand, in the cobalt() complexes [Co(acac) 2 (PN I)]ClO 4 and [Co(acac) 2 (PN II)]ClO 4 two protons of the backbone methylene group of the PN ligands are magnetically inequivalent.