Insight into non-covalent interactions in a [Cu(N3)4]2- bridged hetero-pentanuclear copper(II)/sodium complex with special emphasis on the strong CH•••π[Cu(N3)4] interactions

The hooked cross-shaped anion, [Cu(N-3)(4)](2-), in the pentanuclear hetero-metallic copper(II)-sodium complex, [(CuLNa)(2)(mu-N-3)(2)Cu(N-3)(2)] (1), where H2L = N,N'-bis(3-ethoxysalicylidene)-2,2-dimethylpropane-1,3-diamine (N2O4 donor compartmental Schiff base) is nearly planar and provides a pi-basic surface adequate for establishing non-covalent interactions in the solid state as an electron donor. This unit participates in strong CH center dot center dot center dot[Cu(N-3)(4)](2-) interactions on both sides of the molecular plane. They have been analyzed using DFT calculations and MEP analysis and characterized using NCI plot index analysis along with pi-stacking interactions involving the aromatic and chelate rings of the Na, Cu-coordinated Schiff base ligand. Finally, cation-pi interactions between the pentacoordinated Na-atom and the aromatic ring of the Schiff base ligand are described and compared with two X-ray structures retrieved from the CSD. These unconventional interactions are important for the packing of 1, particularly CH center dot center dot center dot[Cu(N-3)(4)](2-) that has not been studied before, as far as our knowledge extends.

Automated summary

The hooked cross-shaped anion participates in strong CH center dot center dot center dot[Cu(N-3)(4)](2-) interactions in the pentanuclear hetero-metallic copper(II)-sodium complex. DFT calculations, MEP analysis, and NCI plot index analysis were used to analyze and characterize these interactions. Cation-pi interactions between the pentacoordinated Na-atom and the aromatic ring of the Schiff base ligand were described and compared with existing X-ray structures.