Computational Details
All the structures were fully optimized without any symmetry constraints at M06-2X/def2-TZVP level of theory.14 Harmonic vibrational frequency calculations were performed at the same level of theory to understand the nature of the stationary states. All structures were found to be at their local minima with all real values of the Hessian matrix. Unrestricted formalism was adopted for the open shell systems and otherwise mentioned; we observed negligible spin contamination (< 1%) in all open shell calculations. To verify the mono-determinant character of the wavefunction, T1 diagnostic values were evaluated using CCSD(T)/def2-TZVP single point calculations on the M06-2X optimized geometries. Electronic structures of the systems were studied using natural bond orbital (NBO) analyses15 and adaptive natural density partitioning (AdNDP) scheme.16 All these calculations were performed using GAUSSIAN16 suite of program.17
Further, the topological properties of electron density were analyzed within the framework of quantum theory of atoms in molecules (QTAIM)18 and electron localization function (ELF).19 All these calculations were performed using Multiwfn program code.20