Coordination of sorbitol to Ga(OTf) in the liquid phase: an experimental and theoretical study.

In a solution of sorbitol (SBT) and Ga(OTf) compounds, the coordination of sorbitol (SBT) to [Ga(OTf)] ( = 0-3) has been investigated, using both ESI-MS spectra and density functional theory (DFT) calculations at the M06/6-311++g(d,p), aug-cc-pvtz level using a polarized continuum model (PCM-SMD). In sorbitol solution, the most stable conformer of sorbitol includes three intramolecular H-bonds, , O2H⋯O4, O4H⋯O6, and O5H⋯O3. Through ESI-MS spectra, in a tetrahydrofuran solution of both SBT and Ga(OTf) compounds, five main species are observed, , [Ga(SBT)], [Ga(OTf)], [Ga(SBT)], [Ga(OTf)(SBT)], and [Ga(OTf)(SBT)]. Through DFT calculations, in a solution of sorbitol (SBT) and Ga(OTf) compounds, the Ga cation tends to form five six-coordination complexes, , [Ga(η2O,O-OTf)], [Ga(η3O2-O4-SBT)], [(η2O,O-OTf)Ga(η4O2-O5-SBT)], [(η1O-OTf)(η2O2,O4-SBT)Ga(η3O3-O5-SBT)], and [(η1O-OTf)(η2O,O-OTf)Ga(η3O3-O5-SBT)], which are in good agreement with the experimental observation of the ESI-MS spectra. For both [Ga(OTf)] ( = 1-3) and [Ga(SBT)] ( = 1, 2) complexes, the negative charge transfer from ligands to the Ga-center plays an important role in their stability, because of the strong polarization of the Ga cation. For [Ga(OTf)(SBT)] ( = 1, 2; = 1, 2) complexes, the negative charge transfer from ligands to the Ga-center plays an essential role in their stability, accompanied by an electrostatic interaction between the Ga-center and ligands and/or spatial inclusion of ligands toward the Ga-center.