An X-ray crystallographic and DFT study of bis(pyrrolide-imine) nickel(II) Schiff base chelates

•Two novel bis(pyrrolide-imine) nickel(II) Schiff base chelates were synthesized.•The chelates were studied by single crystal X-ray crystallography.•DFT simulations were used to study the solid-state and electronic structures.•Transition energies and oscillator strengths were calculated using TD-DFT.

Two tetradentate N2,N2′ donor bis(pyrrolide-imine) nickel(II) chelates, 2,2′-{(2,2-dimethylpropane-1,3-diyl)bis[nitrilo(E)methylylidene]}bis(pyrrol-1-ide)nickel(II) and 2,2′-{(2-hydroxypropane-1,3-diyl)bis[nitrilo(E)methylylidene]}bis(pyrrol-1-ide)nickel(II), have been synthesized and studied by X-ray crystallography and DFT methods. Both compounds crystallized in the triclinic space group P-1 with three molecules in the asymmetric unit. The chelates have nominally square planar coordination geometry but exhibit puckering to various degrees. The hydroxyl substituent on the di(azomethine) linkage of 2,2′-{(2,2-dimethylpropane-1,3-diyl)bis[nitrilo(E)methylylidene]}bis(pyrrol-1-ide)nickel(II) leads to complementary hydrogen bonding which yields a trimeric supramolecular structure. DFT simulations at the PBEPBE/6-311G(dp) level of theory suggest that a slight puckering of the structures minimizes non-bonded repulsion between the pyrrole δ hydrogen atoms. The puckered structures are ca. 6 kJ mol−1 lower in energy than a planar geometry. TD-DFT was used to delineate the experimental UV–Vis spectra. These simulations accurately predicted the relative intensities of the transitions as well as the wavelengths of the higher energy (π → π∗) transitions.

Graphical abstractTwo tetradentete N2,N2′ donor bis(pyrrolide-imine) nickel(II) chelates have been synthesised, characterised and studied by X-ray crystallography and DFT methods. The chelates exhibit nominally square planar coordination geometry, but are puckered to varying degrees. The hydroxyl substituent on the di(azomethine) linkage allows for complementary hydrogen bonding which yields a trimeric supramolecular structure. DFT simulations suggest that the slight puckering of the structures minimizes non-bonded repulsion between the pyrrole δ hydrogen atoms. TD-DFT was used to delineate the experimental UV-vis spectra.Figure optionsDownload full-size imageDownload as PowerPoint slide