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2 Polish Journal of Chemistry

2 2007

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Lithium-7 NMR and ab initio Calculation Studies of Complexation of Li+ Ion with 12-Crown-4, Benzo-12-crown-4, 15-Crown-5, Benzo-15-crown-5, and Dibenzo-15-crown-5 in Binary Nitromethane-Acetonitrile Mixtures

Shamsipur M., Alizadeh N., Rofouei M. K., Alizadeh K.

Polish Journal of Chemistry

2007

Vol. 81, nr 10

1743-1743

Complexes of 12-crown-4 (12C4), benzo-12-crown-4 (B12C4), 15-crown-5 (15C5), benzo-15-crown-5 (B15C5) and dibenzo-15-crown-5 (DB15C5) with Li+ ion were investigated by lithium-7 NMR in a number of nitromethane (NM)-acetonitrile (AN) binary mixtures. In all cases, the exchange between the free and complexed lithium ionwas fast on the NMR time scale and a single population average resonance was observed. Both 1:1 and 2:1 (sandwich) complexeswere observed between lithium ion and 12C4 and B12C4 in pure nitromethane solution. Stepwise formation constants of the 1:1 and 1:2 (metal/ligand) complexes were evaluated from computer fitting of the NMR mole ratio data to equations which relate the observed metal ion chemical shifts to formation constants. There is an inverse linear relationship between the logarithms of the stability constants and the mole fraction of acetonitrile in the solvent mixtures. The stability of the complexes varies inversely with the Gutmann donor number of the solvent. The stability order of the complexes was found to be 15C5.Li+> B15C5.Li+> DB15C5.Li+> 12C4.Li+ > B12C4.Li+. The optimized structures of the free ligands and their 1:1 and 2:1 complexes with Li+ ionwere predicted by ab initio theoretical calculations using theGaussian 98 software, and the results are discussed.

Comparison of the Proton (H+) and Alkali Metal Ion (Li+, Na+ and K+) Binding Affinities of Pyruvate and Oxamate Anions in the Gas Phase. Quantum-Chemical Studies

Duczmal K., Hallmann M., Raczynska E., Gal F., Maria P.

Polish Journal of Chemistry

2007

Vol. 81, nr 5-6

1011-1020

Proton affinity (PA), lithium, sodium and potassium cation affinities (CA) in the gas phase were estimated by Gaussian-2 (G2), Möller-Plesset (MP2) methods and/or hybrid density functional theory calculations (B3LYP) for pyruvate and oxamate anions. Comparison of these affinities shows that the COO– groups of both anions have similar basicities. Differences between their calculated PAs as well as between their calculated CAs are not larger than 3 kcal mol–1. Somewhat larger differences are evidenced for the formations of the alkali metal complexes with the cation located between the oxygen atoms of the alfaC=O and COO– groups for which the lithium, sodium and potassium cation affinities are larger for oxamate than for pyruvate (by 40.5 kcal mol–1 at theG2 level and by 60.5 kcal mol–1 at the DFT(B3LYP)/6-31++G** level). This is a consequence of the chelate effect on the cation binding seen on the calculatedmost stable structures of the adducts.