On the Significant Importance of Hg···Cl Spodium Bonding/σ/π-Hole/Noncovalent Interactions and Nanoelectronic/Conductivity Applications in Mercury Complexes: Insights from DFT Spectrum

This work synthesized two Hg complexes (1–2) using a L^O-rich ligand (L^O-rich = L^O-VAN/L^ET-VAN) in CH₃OH and CH₃OH/DCM media. Complex 1 is discrete [(HgCl₂)₃L^O-VAN], while 2 is the coordination polymer (CP) [HgCl₂L^ET-VAN]_n. The complexes were characterized using spectroscopy, SCXRD, HRMS, PXRD, SEM-EDX, and XPS study. The X-ray structure revealed that 1 crystallizes in the monoclinic space group P2₁/c and is built from isolated trinuclear units of [(HgCl₂)₃L^O-VAN]. Similarly, 2 crystallizes in the monoclinic space group P2₁/n, having polynuclear units of [HgCl₂L^ET-VAN]_n. The Hg(II) center has favorable stereochemical features and is five-coordinated, creating trigonal (1) and square bipyramidal geometries (2). DFT-D3 at the B3LYP/LanL2DZ level of theory using Gaussian 09 was used to explore the FMO/MEP/NBO and ELF-LOL plot of Hg complexes. Hirshfeld surface and 2D fingerprint plots were used to analyze the H···H, H···O/O···H, and H···Cl/Cl···H contacts. The FMO energy gap explains the complex’s conductivity and nanoelectronic applications. The transfer of electronic charge on the surface has been explained through NBO. ELF-LOL profile demonstrates exceptional complex stability. The existence of spodium bonding (SpBs)/σ-/π-holes and noncovalent interactions was investigated by DFT. The nature and strength of the Hg···Cl SpBs were analyzed by QTAIM and an NCI plot. The findings revealed that SpBs exhibit weak noncovalent interactions characterized by bond critical points (BCPs), bond paths, and reduced density gradient (RDG) iso-surfaces. The MEP surface demonstrated the presence of σ-/π-holes at the Hg atoms, facilitating directional SpB formation. Herein, the nature of the interaction energies is influenced by SpBs and the concurrent formation of additional noncovalent interactions such as π-stacking and CH···π, O contacts. Primarily, the research emphasizes the importance of σ-/π-hole interactions in forming mercury complexes through self-assembly.