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Mer-coordination of a mixed iminoacetamide/(2- picoyl)amine ligand to the zn2+ cation: X-ray and NMR study

In our research of iminodiacetamide (imda) [1] and bis(2-picolyl)amine (bpa) [2] ligands and their coordination to metal cations, we concluded that imda ligands form almost exclusively trans- fac, while bpa ligands gave preferentially cis- fac ML2 isomers. Due to the inherent C2 symmetry of cis- fac or mer ML2 isomers, they are more interesting for potential usage in enantioselective catalysis. By preparation of the mixed imda-bpa tridendate ligand we aimed to increase the probability of metal complexation towards the C2 symmetric structures. Herein we present the preparation and NMR characterization of the mixed iPr-imda-bpa ligand L and its C2 symmetric mer-[ZnL2]2+ complex. 1H and 13C NMR spectra of the ligand and complex in acetonitrile will be compared with theoretical DFT calculations based on a recently proposed scheme, [3] which consists of the exploration of conformer/ rotamer space by the CREST algorithm [4] and calculations of the free energies and Boltzmann populations by the ENSO utility. [3] Calculation of NMR parameters is performed by the ORCA program. [5] Additionally, we present a solid-state structure of the mer [ZnL2]2+ complex obtained by single-crystal X-ray diffraction. Single crystals are prepared by complexation of the ligand L with Zn(BF4)2·× H2O. The crystal structure includes the SiF6 2– anions as a result of the decomposition of BF4 – anions and reaction of the formed F– anions with the glass vessel. [1] Obtained crystals of 2[ZnL2] [SiF6][BF4]2 × 8.5H2O solvate crystallize in the highly symmetric cubic space group Pn3n (Nr. 222, a = 37.10182(10) Å) with 48 mer [ZnL2]2+ cations in the unit cell.

crystal structure ; zinc complex ; X-ray diffraction ; NMR

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