The synthesis and characterization of the perchlorate salts of the copper(I), copper(II), zinc(II), cobalt(II), and iron(II) complexes of 2, 6-bis[1-((1-(carboxymethyl)-2-imidazol-4-ylethyl)imino)ethyl]pyridine = L-bisp (the condensation product of 2, 6-diacetylpyridine with two molecules of the methyl ester of the amino acid L-histidine) along with an X-ray structural investigation of the zinc(II) complex, [Zn(L-bisp)][ClO 4 ] 2 , are reported. The zinc complex crystallizes in the space group D 2 4 -P2 1 2 1 2 1 four formula units in a cell of dimensions (at-152 °C) a = 28.872 (18) Å, b = 9.567 (6) Å, and c = 10.344 (6) Å. The structure was described by 406 variable parameters, and at convergence the values for R and R w (on F 2 , 5784 data) were 0.060 and 0.090 for the L,L enantiomer. The zinc atom is bonded to five nitrogen atoms and displays a coordination geometry intermediate between a trigonal bipyramid and a square pyramid. Both of the six-membered amino acid chelate rings of the L-bisp ligand adopt the λ configuration. The Cu(I) complex is inert to dioxygen in the solid state but does react with O 2 at ambient conditions in dry acetonitrile. The reaction is complete in ca. 1 h and can be slowly reversed by degassing (N 2 ) and gentle heating, the degree of reversibility being about 80% for each of several oxy-deoxy cycles. Spectral evidence indicates the oxygenated product is not simply [Cu(L-bisp)] [ClO 4 ] 2 and that the L-bisp ligand remains intact. The stoichiometry of the oxygenation reaction is 0.5 mol (±10%) of O 2 /mol of copper. Both the Fe(II) and the Co(II) complexes of L-bisp show low or no reactivity to dioxygen in dry acetonitrile or dimethylformamide. However, pyridine solutions of these two complexes do react irreversibly with O 2 at ambient conditions and, in both cases, IR evidence is indicative of concomitant ligand oxidation.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry