Noncovalent Mg···N Interactions as Tunable Electronic Perturbations in Pyridine-Based Single-Molecule Junctions

This work presents a comprehensive theoretical investigation of magnesium-to-nitrogen (Mg···N) noncovalent interactions in substituted pyridine-MgH₂ (X-Pyr.MgH₂) complexes and their implications for single-molecule electron transport. Geometry optimization, binding-energy analysis, AIM, NBO, and SAPT calculations reveal electrostatically dominated Mg···N interactions with strengths ranging from -100.03 to -77.29 kJ/mol, modulated systematically by the substituent-dependent basicity of the pyridine ring. Complex formation induces measurable structural perturbations and a pronounced reduction (1-2.5 eV) in the HOMO-LUMO energy gap. DFT-NEGF simulations of Au-molecule-Au junctions show that Mg···N bonding significantly alters transmission characteristics, producing distinct quantum interference features and a substituent-dependent suppression of current near the Fermi level. The resulting I-V responses exhibit stepwise "Coulomb staircase'' behaviour, indicating quantized charge transport across the junction. These results establish Mg···N noncovalent interactions as tunable electronic perturbations that can modulate conductance in pyridine-based single-molecule junctions, providing a feasible molecular framework for exploring single-electron transistor-like behaviour.