A Comprehensive Theoretical Characterization on All-Silicon Rings, Cyclo[n]Silicons (n = 8, 10, 12, 14): Structure, Bonding, and Aromaticity.

Cyclo[n]silicons (Sin), all-silicon rings composed solely of silicon atoms, represent a new class of molecular silicon allotropes analogous to cyclo[n]carbons. Here we present a systematic theoretical study on representative Sin (n = 8, 10, 12, 14), investigating their geometric structure, bonding configurations, and aromaticity. All examined silicon rings can exist as stable crown-like structures in the gas phase. Electronic structure and bonding analyses reveal that Si-Si bonding is dominated by σ interactions but also contains π contributions. Real-space analyses indicate that electron delocalization becomes more pronounced as the ring size decreases. Magnetic criteria further reveal that Si8 and Si10 exhibit antiaromatic magnetic responses mainly associated with σ-conjugation, whereas Si12 and Si14 show much weaker magnetic responses and are close to nonaromatic. These results establish the fundamental bonding and aromaticity patterns of all-silicon cyclic molecules and provide theoretical insight into the design of silicon-based molecular rings.