Yunseop Choi (POSTECH)

Jongcheol Seo (POSTECH)

Yunseop Choi (POSTECH)

Jongcheol Seo (POSTECH)

Ligand geometry plays an important role in determining metal ion coordination behavior and can strongly influence the structures and growth of ligand-bound ionic clusters. In this work, we employed bipyridine isomers with rigid donor geometries to investigate how ligand geometry affects the formation of alkali halide cluster ions. Ligand-bound alkali halide clusters generated by electrospray ionization (ESI) were characterized using ion mobility spectrometry-mass spectrometry (IMS-MS), and their structures were assigned through comparison of experimental and theoretical collision cross section (CCS) values obtained from density functional theory (DFT) calculations. The combined IMS-MS and DFT results reveal that 2,2’-bipyridine coordinates to individual Li+ ions through bidentate chelation, whereas 3,3’-bipyridine preferentially bridges multiple Li+ centers within LiI ionic clusters. These distinct coordination modes lead to fundamentally different cluster growth behaviors between 2,2’-bipyridine and 3,3’-bipyridine. 2,2’-bipyridine suppress cluster growth by stabilizing isolated coordination complexes, whereas 3,3’-bipyridine stabilizes progressively larger LiI clusters and can even alter the preferred structures of their ionic cores. In contrast, 4,4’-bipyridine exhibits only weak coordination because its donor atoms are too widely separated to efficiently support either chelating or bridging coordination. Comparison with our previous study on flexible diamine ligands further demonstrates that ligand flexibility and donor geometry play important roles in governing ligand-assisted ionic cluster assembly. These findings reveals a close relationship between ligand geometry, coordination mode, providing molecular level insight into ligand-directed alkali halide cluster assembly.

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