Tailoring the Superatomic\nCharacteristics and Optical\nBehavior of Metal-Free Boron Clusters via Ligand Engineering

It is of great importance to understand how the number\nand type\nof ligands influence the properties of clusters through ligand engineering,\nas this knowledge is crucial for the rational design and optimization\nof functional materials. Herein, the geometrical structures, binding\nenergies, and electronic properties of nonmetallic B<sub>n</sub> (n\n= 20 and 40) clusters with CO, PEt<sub>3</sub>, F, NO<sub>2</sub>,\nand CN ligands are systematically explored based on density functional\ntheory (DFT) calculations. Our findings demonstrate that the CO ligand\nacts as an electron donor when attached to these two boron clusters,\nin contrast to their role as electron acceptors in interactions with\nmetal oxide and metal chalcogenide clusters. This emphasizes the necessity\nof considering the intrinsic properties of the host cluster when modifying\nwith ligands. Moreover, it was observed that substituting PEt<sub>3</sub> with F, NO<sub>2</sub>, or CN converted the B<sub>20</sub> cluster from an electron acceptor to an electron donor, thereby\ndemonstrating the versatility in tuning the redox characteristics\nof boron clusters by selecting appropriate ligands. Intriguingly,\nthe attachment of the PEt<sub>3</sub>, F, NO<sub>2</sub>, and CN ligands\nto B<sub>20</sub> can significantly modulate the electronic properties\nof B<sub>20</sub> to realize the formation of metal-free superalkali\n(B<sub>20</sub>(PEt<sub>3</sub>)<sub>n</sub>, n = 3–5) and\nsuperhalogen (B<sub>20</sub>F, B<sub>20</sub>NO<sub>2,</sub> and B<sub>20</sub>CN) clusters. Furthermore, the structure, stability, and\noptical absorption of the charge transfer complex B<sub>20</sub>(PEt<sub>3</sub>)<sub>3</sub><sup>+</sup>B<sub>20</sub>F were analyzed. This\ncomplex has been identified as an efficient material for harvesting\nvisible light. Our findings provide insights into the effects of ligand\nvariations on boron cluster functionalities, offering a new perspective\nfor the design of advanced materials with tailored cluster properties\nthrough ligand engineering.