Manipulating Clusters by Use of Competing N,O‐Chelating Ligands: A Combined Crystallographic, Mass Spectrometric, and DFT Study

Two heptanuclear discs, [Co 7 (L1) 6 (CH 3 O) 6 ] 2+ ( Co 7 ‐L1 ) and [Co 7 (L2) 12 ](ClO 4 ) 2 ( Co 7 ‐L2 ), have been prepared by the reaction of [Co(H 2 O) 6 ](ClO 4 ) 2 with Schiff base HL1 (HL1=2‐methoxy‐6‐[(methylimino)methyl]phenolate) or benzimidazole derivative HL2 (HL2=(1 H ‐benzo[ d ]imidazol‐2‐yl)methanolate), respectively, at room temperature. In contrast, the reaction of [Co(H 2 O) 6 ](ClO 4 ) 2 with a mixture of the two ligands, having similar coordination ability but different shapes, resulted in the butterfly‐structured tetranuclear cobalt cluster [Co 4 (L1) 2 (L2) 4 ](ClO 4 ) 2 ⋅ 2H 2 O ( Co 4 ). Electrospray ionization mass spectrometry (ESI‐MS) analysis in real time revealed the {Co 1 }→{Co 2 }→{Co 4 }→{Co 7 } stepwise assembly when a single ligand was employed, but when both ligands were used only {Co 4 } was obtained, an intermediate of the former reactions. Interestingly, ligand competition was evidenced in the assembly process of the reaction with two ligands; for example, [Co 4 (L1) 4 (L2) 2 ] 2+ and [Co 4 (L1) 3 (L2) 3 ] 2+ were the primary clusters observed at the beginning of the reaction, but [Co 4 (L1) 2 (L2) 4 ] 2+ was the final product. This observation suggests ligand exchange is taking place, and DFT calculations confirmed that these transformations were possible. By varying the ratio of ligands, the abundance of a certain species in the competitive reaction could be controlled.