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