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

Abstract

The hooked cross-shaped anion, [Cu(N₃)₄]²⁻, in the pentanuclear hetero-metallic copper(II)–sodium complex, [(CuLNa)₂(μ-N₃)₂Cu(N₃)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 π-basic surface adequate for establishing non-covalent interactions in the solid state as an electron donor. This unit participates in strong CH⋯[Cu(N₃)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 π-stacking interactions involving the aromatic and chelate rings of the Na, Cu-coordinated Schiff base ligand. Finally, cation–π 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⋯[Cu(N₃)₄]²⁻ that has not been studied before, as far as our knowledge extends.