However, in the case of Cu18PTT NC, although it exhibits a core-shell architecture but an alteration of its core and shell is quite distinct than previous (Figure ). It exhibits a Cu9 core which is intricately surrounded by three Cu3S5P2 motif units. Interestingly, the details structural analysis revealed that the Cu9 core is formed by fusion of two Cu5 triangular bipyramidal geometries through a vertex Cu atom sharing (Figure ). So, the change in the reducing agent expand the NC architecture by suggesting a more compact and robust structure. The total length of this fused core extends to about 7.4353Å, whereas the length of one Cu5 unit is 3.7564Å. This suggests that the kernel fusion not only enlarges the core but also confines it through stronger cuprophilic interactions. Although the fusion confines the core geometry but the change of the PTT ligand with ABT, the confinement effect is more prominent which squeezed the core with much effectively. So, the confinement of the core Cu atoms mostly depends on the electronic environment of the surface protecting ligands and the overall geometrical architecture of the NC. Additionally, the fusion process extends to the motif units of Cu18PTT NC. Here, two Cu2S3P2 motif units fused via a terminal Cu atom to create a modified Cu3S5P2 motif unit. This modification results in the loss of one triphenylphosphine unit, a change facilitated by the inward orientation of the shared Cu atom, which discourages further attachment of the bulky ligand. Thus, as the core size increases due to kernel fusion, there is a corresponding evolution in the motif units to appropriately complement the enlarged core. Regarding bond lengths, the Cu-S bonds within these motif units range from 2.2114 to 2.3722Å (average 2.2644±0.0072Å).