Structural Determination of the Hexacoordinated [Zn(L)2]2+ Complex Isomer Type Using Solution-State NMR, DFT Calculations and X-ray Crystallography

The isomerism of zinc complex [Zn(L)(2)](2+) with tridentate ligand L having acetamide and pyridine groups on each side of the central amino- nitrogen atom has been investigated by DFT calculations, liquid state NMR and single-crystal X-ray diffraction. DFT was used for obtaining the ensembles of low-energy conformers of L and [Zn(L)(2)](2+) and for the calculation of NMR parameters for all conformers. For all generated conformers of L and [Zn(L)(2)](2+), the Mean Absolute Error [MAE(conf)] was tested as a structural quality parameter and compared with MAE(Bolz) for Boltzmann weighted ensembles. The most populated conformers had MAE(conf) values below 0.1 and 1 ppm for H-1 shifts and C-13 shifts, respectively. For the [Zn(L)(2)](2+) complex, the mer- C-2 symmetric isomer was the most stable, in accordance with the X-ray structure of [Zn(L)(2)](2)[SiF6][BF4](2). The cancellation of the magnetic equivalence of some nuclei valid for free L, when coordinated to the Zn2+ cation, was theoretically explained by the correct averaging of NMR parameters in the calculation procedure.

Automated summary

The isomerism of zinc complex [Zn(L)(2)](2+) with tridentate ligand L was studied using DFT calculations, liquid state NMR, and single-crystal X-ray diffraction. The most stable isomer of [Zn(L)(2)](2+) complex was found to be mer-C-2 symmetric, consistent with the X-ray structure. The cancellation of magnetic equivalence in some nuclei upon coordination to Zn2+ cation was explained by averaging of NMR parameters in the calculation procedure.