Structural Isomerism\nin Bimetallic Ag<sub>20</sub>Cu<sub>12</sub> Nanoclusters

Structural isomers of atomically precise metal nanoclusters\nare\nhighly sought after for investigating structure–property relationships\nin nanostructured materials. However, they are extremely rare, particularly\nthose of alloys, primarily due to the challenges in their synthesis\nand structural characterization. Herein, for the first time, a pair\nof bimetallic isomeric AgCu nanoclusters has been controllably synthesized\nand structurally characterized. These two isomers share an identical\nmolecular formula, Ag<sub>20</sub>Cu<sub>12</sub>(CCR)<sub>24</sub> (denoted as <b>Ag</b><sub><b>20</b></sub><b>Cu</b><sub><b>12</b></sub><b>-1</b> and <b>Ag</b><sub><b>20</b></sub><b>Cu</b><sub><b>12</b></sub><b>-2</b>; HCCR is 3,5-bis(trifluoromethyl)phenylacetylene).\nSingle-crystal X-ray diffraction data analysis revealed that <b>Ag</b><sub><b>20</b></sub><b>Cu</b><sub><b>12</b></sub><b>-1</b> possesses an Ag<sub>17</sub>Cu<sub>4</sub> core\ncomposed of two interpenetrating hollow Ag<sub>11</sub>Cu<sub>2</sub> structures. This core is stabilized by four different types of surface\nmotifs: eight –CCR, one Cu(CCR)<sub>2</sub>, one Ag<sub>3</sub>Cu<sub>3</sub>(CCR)<sub>6</sub>, and\ntwo Cu<sub>2</sub>(CCR)<sub>4</sub> units. <b>Ag</b><sub><b>20</b></sub><b>Cu</b><sub><b>12</b></sub><b>-2</b> features a bitetrahedron Ag<sub>14</sub> core, which\nis stabilized by three Ag<sub>2</sub>Cu<sub>4</sub>(CCR)<sub>8</sub> units. Interestingly, <b>Ag</b><sub><b>20</b></sub><b>Cu</b><sub><b>12</b></sub><b>-2</b> undergoes\nspontaneous transformation to <b>Ag</b><sub><b>20</b></sub><b>Cu</b><sub><b>12</b></sub><b>-1</b> in the solution-state.\nDensity functional theory calculations explain the electronic and\noptical properties and confirm the higher relative stability of <b>Ag</b><sub><b>20</b></sub><b>Cu</b><sub><b>12</b></sub><b>-1</b> compared to <b>Ag</b><sub><b>20</b></sub><b>Cu</b><sub><b>12</b></sub><b>-2</b>. The\ncontrolled synthesis and structural isomerism of alloy nanoclusters\npresented in this work will stimulate and broaden research on nanoscale\nisomerism.