Coordination of sorbitol to Ga(OTf) 3 in the liquid phase: an experimental and theoretical study.

In a solution of sorbitol (SBT) and Ga(OTf) 3 compounds, the coordination of sorbitol (SBT) to [Ga(OTf) n ] 3- n ( n = 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, i.e. , O2H⋯O4, O4H⋯O6, and O5H⋯O3. Through ESI-MS spectra, in a tetrahydrofuran solution of both SBT and Ga(OTf) 3 compounds, five main species are observed, i.e. , [Ga(SBT)] 3+ , [Ga(OTf)] 2+ , [Ga(SBT) 2 ] 3+ , [Ga(OTf)(SBT)] 2+ , and [Ga(OTf)(SBT) 2 ] 2+ . Through DFT calculations, in a solution of sorbitol (SBT) and Ga(OTf) 3 compounds, the Ga 3+ cation tends to form five six-coordination complexes, i.e. , [Ga(η2O,O-OTf) 3 ], [Ga(η3O2-O4-SBT) 2 ] 3+ , [(η2O,O-OTf)Ga(η4O2-O5-SBT)] 2+ , [(η1O-OTf)(η2O2,O4-SBT)Ga(η3O3-O5-SBT)] 2+ , 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) n ] 3- n ( n = 1-3) and [Ga(SBT) m ] 3+ ( m = 1, 2) complexes, the negative charge transfer from ligands to the Ga 3+ -center plays an important role in their stability, because of the strong polarization of the Ga 3+ cation. For [Ga(OTf) n (SBT) m ] 3- n ( n = 1, 2; m = 1, 2) complexes, the negative charge transfer from ligands to the Ga 3+ -center plays an essential role in their stability, accompanied by an electrostatic interaction between the Ga 3+ -center and ligands and/or spatial inclusion of ligands toward the Ga 3+ -center.