As part of our efforts towards computation assisted engineering of functional molecules, we studied how substituents with different EW/ED properties affect the singlet ground and quintet excited state properties of the [Fe(terpy)2] 2+ complex, when substituted on the molecular axis (at the 4' position of the ligands). DFT calculations and various experimental methods (NMR, Mössbauer, XRD) showed that in the ground state the impact is minimal on the molecular geometry, yet the electron density variations are clearly observed on the axial N atoms. Calculated shifts in orbital energies are reflected in oxidation/reduction potentials and UV-VIS spectra.