In this thesis we will used density functional theory to investigate the directional features of the metal-ligand (M 2 -L) bonds. To understand the origin of directionality in these complexes, it is essential to know the physical forces governing the interactions. To this end, we used different energy decomposition analysis methods, to partition the interaction energies to physically meaningful components. As a starting point, we considered the complexes between the simplest clusters of coinage metals, that is , and also AuCu, AgCu and ammonia, as a universal electron donor. Our calculations show that the linear arrangement with a M?M?L angle,, of is the energetically most favorable geometry of the complexes. We performed a scan of angle from the linear to the perpendicular ( ) arrangements, in the steps of 10 degrees, and performed NEDA and IQA calculation on the aforementioned structures. Although, molecular electrostatic potential (ESP) maps predict that the electrostatic interactions are responsible for the directionality of M-N bonds, NEDA calculations indicate that electrostatic term favors slightly the perpendicular M-M-N arrangement. Indeed, the linear geometry is preferred because the sum of charge transfer and Pauli repulsion terms is more favorable in the linear arrangement. Interacting quantum atoms (IQA) analysis shows that inter-atomic interactions favor the perpendicular geometries, however, these terms are compensated by the atomic self-energies, which are more favorable in the linear arrangement.
