title: 7Li NMR chemical shift titration and theoretical DFT calculation studies: solvent and anion effects on second-order complexation of 12-crown-4 and 1-aza-12-crown-4 with lithium cation in several aprotic solvents.
abstract: (7)Li NMR titration was used to determine stepwise complexation constants for the second-order complexation of lithium cation with 12-crown-4 in acetonitrile, propylene carbonate and a binary mixture of propylene carbonate and dimethyl carbonate. The anions used were perchlorate, hexaflurophosphate and trifluromethanesulfonate. A second ligand 1-aza-12-crown-4 was similarly investigated. The exchange between the free and complexed cation in these reactions is fast on an NMR timescale resulting in a single lithium peak which is a concentration-weighted average of the free and bound species. Solvent effects show that the 1:1 complex is much more stable in acetonitrile than in propylene carbonate or in the propylene carbonate dimethyl carbonate mixture. Anion effects for a given solvent were small. Optimized geometries of the free ligands and the 1:1 and 1:2 (sandwich) metal-ligand complexes were predicted by hybrid-density functional theory using the Gaussian 03 software package. Results were compared to literature values for 1:1 stability constants found by microcalorimetry for several of these systems and are found to be in good agreement. Although microcalorimetry only considered the formation of 1:1 complexes, (7)Li NMR shows evidence that both 1:1 and 1:2 complexes should be considered.
authors: Department of Chemistry, University of Utah, Salt Lake City, Utah 84112-0850, USA.
authors: Marilyn C
authors: MC
authors: Masiker
authors: Charles L
authors: CL
authors: Mayne
authors: Brian J
authors: BJ
authors: Boone
authors: Anita M
authors: AM
authors: Orendt
authors: Edward M
authors: EM
authors: Eyring
mesh_terms: D000465:Algorithms; D000838:Anions / Q000737:chemistry; D002151:Calorimetry; D002412:Cations / Q000737:chemistry; D003198:Computer Simulation; D043844:Crown Ethers / Q000737:chemistry*; D008024:Ligands; D008094:Lithium / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D009942:Organometallic Compounds / Q000737:chemistry; D011789:Quantum Theory; D012997:Solvents / Q000737:chemistry*
chemical_list: C480580:1-aza-12-crown-4; D000838:Anions; D002412:Cations; D043844:Crown Ethers; D008024:Ligands; D009942:Organometallic Compounds; D012997:Solvents; D008094:Lithium