Synthesis and Characterization of a Tetradentate Bispidine-based Ligand and its Zinc(II) Complex

The efficient synthesis of a tetradentate diol-bispidine-based ligand and its metal complex with Zn(II) is here reported. The single-crystal X-ray diffraction (SC-XRD) analysis of the Zn(II) complex allowed the characterization of the coordination sphere around the cation as a distorted square pyramid and confirmed that the bispidine core was in a chair-chair (cc) conformation. This finding agreed with the theoretical analysis. The structural data demonstrated the influence of the ligand conformation on the coordination mechanism, confirming that the cc geometry of the bispidine core is a key factor to form a stable complex. Hirshfeld surface and two-dimensional fingerprint analysis showed that hydrogen bonds (O···H) and van der Waals interactions constituted the major contribution to the intermolecular forces, with O···H/H···O and H···H contacts accounting for 39.8% and 38.8% of the surface, respectively. NMR titration experiments provided information on the formation mechanism of the complex and on the species formed throughout the reaction.