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

Abstract

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 1H shifts and 13C shifts, respectively. For the [Zn(L)2]2+ complex, the mer- C2 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.