Abstract
We report here the synthesis and characterization of two endohedral Zintl-ion clusters, [Fe(4)Sn(18)](4-) and [Fe(4)Pb(18)](4-), which contain rhombic Fe(4) cores. The Fe-Fe bond lengths are all below 2.5 Å, distinctly shorter than in the corresponding Cu clusters, indicating the presence of Fe-Fe bonding. Subtle differences in the structure of the Fe(4) core between the two clusters suggest that the change in tetrel element causes a change in electronic ground state, with a very short Fe-Fe bond length of 2.328 Å present across the diagonal of the rhombus in the lead case.