Electron deficient nature is one of the reasons for the diversity of the geometrical structures of Group 14 clusters. While some clusters can be stabilized by bulky ligands from the outside, the others can be supported internally by transition metal (TM) atoms to compensate their electron deficiency. For example, a capsule-like cluster composed of 17 Sn atoms was previously shown to be stable due to the inner support of 2 Pt atoms in a [Pt2@Sn₁₇]^4- cluster. Is it a crucial requirement to have 2 TM atoms to support Sn cages in a similar size range, or would it be possible to stabilize such a structure by just one Pt atom? In this poster, I will show that the removal of one Pt atom results in the collapse of the capsule-like geometry of [Pt2@Sn₁₇]^4- due to the electron deficiency of the cage, leading to the unprecedented single-metal-encapsulated double-cage structure of [Pt@Sn₁₇]^4-. Our DFT calculations on the recently synthesized [Pt@Sn₁₇]^4- complex show that the lack of the support from the inner TM atoms is responsible for the dramatic geometric change. Deviation from the higher possible symmetry was found to be due to the Jahn-Teller effect, stemming from the vibronic coupling of certain occupied and unoccupied molecular orbitals, lowering the symmetry from C_2v to C_s. Electron localization via AdNDP analysis has confirmed the electron deficient nature of the [Pt@Sn₁₇]^4- cluster, revealing delocalized 3c-2e and 4c-2e bonding interactions pervading throughout the molecule.

Asymmetrical fusion of two inhomogeneous building units [Pt@Sn<sub>9</sub>] and [Sn<sub>9</sub>] leads to the largest group 14 intermetalloid cluster [Pt@Sn<sub>17</sub>]<sup>4−</sup> encapsulating a single transition metal atom. The unusual double-cage structure could be seen as a result of the collapse of the capsule-like Sn<sub>17</sub> framework when filled with only one Pt atom.

Asymmetrical fusion of two inhomogeneous building units [Pt@Sn₉] and [Sn₉] leads to the largest group 14 intermetalloid cluster [Pt@Sn₁₇]⁴⁻ encapsulating a single transition metal atom. The unusual double-cage structure could be seen as a result of the collapse of the capsule-like Sn₁₇ framework when filled with only one Pt atom.

Hong-Lei Xu

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