Atomically Precise Platinum Carbonyl Nanoclusters: Synthesis, Total Structure, and Electrochemical Investigation of [Pt(27)(CO)(31)](4–) Displaying a Defective Structure

[Image: see text] The molecular Pt nanocluster [Pt(27)(CO)(31)](4–) (1(4–)) was obtained by thermal decomposition of [Pt(15)(CO)(30)](2–) in tetrahydrofuran under a H(2) atmosphere. The reaction of 1(4–) with increasing amounts of HBF(4)·Et(2)O afforded the previously reported [Pt(26)(CO)(32)](2–) (3(2–)) and [Pt(26)(CO)(32)](−) (3(–)). The new nanocluster 1(4–) was characterized by IR and UV–visible spectroscopy, single-crystal X-ray diffraction, direct-current superconducting quantum interference device magnetometry, cyclic voltammetry, IR spectroelectrochemistry (IR SEC), and electrochemical impedance spectroscopy. The cluster displays a cubic-close-packed Pt(27) framework generated by the overlapping of four ABCA layers, composed of 3, 7, 11, and 6 atoms, respectively, that encapsulates a fully interstitial Pt(4) tetrahedron. One Pt atom is missing within layer 3, and this defect (vacancy) generates local deformations within layers 2 and 3. These local deformations tend to repair the defect (missing atom) and increase the number of Pt–Pt bonding contacts, minimizing the total energy. The cluster 1(4–) is perfectly diamagnetic and displays a rich electrochemical behavior. Indeed, six different oxidation states have been characterized by IR SEC, unraveling the series of 1(n–) (n = 3–8) isostructural nanoclusters. Computational studies have been carried out to further support the interpretation of the experimental data.