Elucidation of the electronic structure of atomically precise [Pt17(CO)12(PPh3)8] z [Pt17(CO)12(PPh3)8] z was synthesized through a polyol reduction and ligand-exchange method, similar to that in previous reports. Briefly, the Pt precursor was heated to 120 °C in ethylene glycol with sodium hydroxide under atmospheric conditions. The solution was then cooled to room temperature, and PPh3 was added to form Ptn(CO)m(PPh3)l NCs. From the obtained products, [Pt17(CO)12(PPh3)8] z was selectively isolated using solvent extraction. The resulting product was confirmed to be high-purity [Pt17(CO)12(PPh3)8] z via electrospray ionization mass spectrometry (ESI-MS; Fig. ). Figure shows the optical absorption spectrum of [Pt17(CO)12(PPh3)8] z , which presents prominent peaks at approximately 1.10, 1.20, 1.85, and 2.15 eV, indicating a discrete electronic structure similar to that of Au25(PET)18 (PET = 2-phenylethanethiolate) and its alloy NCs. DFT calculations were conducted to elucidate the origin of peaks observed in the optical absorption spectrum of [Pt17(CO)12(PPh3)8] z by the Gaussian 16 program , and B3LYP functional was adopted (basis set; the Stuttgard/Dresden basis set with effective core potentials for Pt, 6-311+G* for P, C, O, and H). This study focused on the closed-shell electronic systems of [Pt17(CO)12(PPh3)8] 2+ owing to the computational complexity of the open-shell systems in [Pt17(CO)12(PPh3)8] 1+ . To reduce computational burden, the phenyl groups (Ph3) were replaced with methyl groups (CH3)3. Geometry optimization was performed based on the structure of [Pt17(CO)12(PPh3)8] 2+ obtained by single crystal X-ray diffraction (Fig. ), followed by time-dependent (TD)-DFT calculations for the optical absorption spectrum using the optimized geometric structure of [Pt17(CO)12(PPh3)8] 2+ .