Synthesis, Structure, and Electronic Properties of [Cr6@Sn8Sb8(en)2]3–: A Cr6 Octahedron Encapsulated in a Zintl-Ion Ligand

Abstract

The reaction of CrCp2 with K2SnSb yields a Zintl-ion cluster containing an octahedral Cr6 core, surrounded by an Sn8Sb8 ring and two further ethylenediamine ligands that cap two mutually trans Cr centers. The Cr–Cr bond lengths of 2.453(2) to 2.482(2) Å are remarkably short, much shorter than those in any of the 20-electron chalcogenide-capped analogues, Cr6E8(PR3)6, indicating unusually strong Cr–Cr bonding. An isotropic signal in the electron paramagnetic resonance (EPR) spectrum with g = 2.21 is consistent with a 23-electron Cr613+ core, three electrons more reduced than the Cr616+ units present in Cr6E8(PR3)6. An analysis of the electronic structure using density functional theory (DFT) indicates that the additional three electrons enter Cr–Cr bonding orbitals, which are stabilized as a result of the weak π-donor properties of the Sn8Sb816– Zintl ligand.