Supramolecular Interactions in Copper(II) Second Sphere Complex, [Cu(en)2(H2O)2](2-hydroxy-2-phenylacetate)2: Synthesis, Characterization, Single Crystal X-ray Structural Study, DFT, and Hirshfeld Surface Analysis

Novel ethylenediamine copper(II) complex, [Cu(en)₂(H₂O)₂](2-hydroxy-2-phenylacetate)₂ have been synthesized by the addition of en (ethylenediamine) to copper(II) 2-hydroxy-2-phenylacetate in methanol : water (4:1, v/v) solution. The newly synthesised complex was characterised by elemental analyses, spectroscopic techniques (UV–Vis, FT-IR,), magnetic moment, molar conductivity measurement, thermogravimetric analysis, field electron scanning microscopy (FESEM), energy dispersive X-ray spectra (EDS) which indicated the presence of ionic complex with CuN₄O₂ chromophore. Single-crystal X-ray structural analysis revealed that copper(II) complex crystallizes in orthorhombic crystal system with Pbca space group and cell dimensions: a = 12.0266(6) Å, b = 7.9119(3) Å, c = 26.4374(12) Å, α = β = γ = 90°. Further, single crystal structure determination divulged the existence of second sphere complex with distorted octahedral geometry. Copper(II) complex consists of cationic moiety [Cu(en)₂(H₂O)₂]²⁺ and two discrete anionic moieties, 2-hydroxy-2-phenylacetate ions. Besides electrostatic forces of attraction, non-covalent interactions (hydrogen bonding and C–H···π) stitch the second sphere complex into extended three-dimensional supramolecular architecture and provide robustness to the crystal lattice. DFT investigation however displayed four coordinated distorted square planar copper(II) complex with two water molecules (at a distance < 2.593 Å) approaching the metal ion in order to provide octahedral geometry to the complex essential for packing efficiency of the crystal.