Guanidinium-based scaffolds have long been recognised for their ability to function as general-acid catalysts, and therefore we decided to conduct an extensive computational investigation to gain a deeper understanding of the interactions that occur upon complexation. To ensure clarity and avoid clutter, we present the key findings from our analysis of both neutral (guanide-based) and charged (guanidinium-based, Figure ) complexes in the Supplementary Information (Figures S1-S4 and Tables ), utilising the same methodologies as before, i.e. LMO-EDA, QTAIM and NBO. The calculated interaction energies for both the neutral and charged complexes were found to be negative, as anticipated. Furthermore, the interaction energies for the neutral complexes were consistently lower than those for the charged complexes. In particular, an unexpected case that warrants attention concerns the guanidininium t Bu complexes, which exhibited interaction energies that were one order of magnitude lower than the rest of the charged complexes under investigation. When the monomer and the complexes were carefully examined, it became evident that accommodating the anion within such a bulky species re-quires substantial deformation energy. However, looking at the LMOEDA total energies the results are consistent amongst the three substituents and present the expected stability trend. The distance between positively charged N + and negatively charged X -ranged from 2.65 to 3.43 Å, higher than in the cases previously analysed.