Ternary aromatic and anti-aromatic clusters derived from the hypho species [Sn2Sb5]3−

Abstract

Heterometallic clusters have attracted broad interests in the synthetic chemistry due to their various coordination modes and potential applications in heterogeneous catalysis. Here we report the synthesis, experimental, and theoretical characterizations of four ternary clusters ([M₂(CO)₆Sn₂Sb₅]³⁻ (M = Cr, Mo), and [(MSn₂Sb₅)₂]⁴⁻, (M = Cu, Ag)) in the process of capturing the hypho- [Sn₂Sb₅]³⁻ in ethylenediamine (en) solution. We show that the coordination of the binary anion to transition-metal ions or fragments provides additional stabilization due to the formation of locally σ-aromatic units, producing a spherical aromatic shielding region in the cages. While in the case of [Mo₂(CO)₆Sn₂Sb₅]³⁻ stabilization arises from locally σ-aromatic three-centre and five-centre two-electron bonds, aromatic islands in [(AgSn₂Sb₅)₂]⁴⁻ and [(CuSn₂Sb₅)₂]⁴⁻ render them globally antiaromatic. This work describes the coordination chemistry of the versatile building block [Sn₂Sb₅]³⁻, thus providing conceptual advances in the field of metal-metal bonding in clusters.

Ternary heterometallic clusters often display intriguing structures and bonding. Here the authors prepare four [Sn₂Sb₅]³⁻-based clusters stabilized by coordination of a transition metal ion; analysis of their electronic structure reveals that the resulting cluster displays globally aromatic or antiaromatic character depending on the transition metal ion.