Nuclear magnetic resonance study of the stoichiometry and stability of lithium ion complexes with two small size crown ethers in binary nitromethane-acetonitrile mixtures

作者：Alizadeh Nina^*; Shamsipur Mojtaba

来源：Journal of Inclusion Phenomena and Macrocyclic Chemistry, 2010, 68(3-4): 431-436.

DOI：10.1007/s10847-010-9806-4

• Macrocyclic complexes
• Crown ethers
• Lithium ion
• Lithium-7 NMR
• Complexation constants
• Nitromethane acetonitrile mixtures

Lithium-7 NMR spectrometry was used to study the complexation reaction between lithium ions and different small size crown ethers12-crown-4 (12C4), benzo-12-crown-4 (B12C4) in a number of binary nitromethane (NM)-acetonitrile (AN) mixtures. The exchange between the free and complexed lithium ion was fast on the NMR time scale and a single population average resonance was observed. Both 1:1 and 2:1 (sandwich) complexes were observed between lithium ion and 12C4 and B12C4 in pure nitromethane solution. Stepwise formation constants of the 1:1 and 2:1 (ligand/metal) 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 order of the 1:1 and 2:1 complexes was found to be 12C4.Li(+) > B12C4.Li(+). The optimized structures of the free ligands and their 1:1 and 2:1 complexes with Li(+) ion were predicted by ab initio theoretical calculations using the Gausian 98 software, and the results are discussed.

• 出版日期2010-12