The pentacoordinated [Cr(CO)₅]²⁻ dianion in [2,2,2-crypt-K]₂[Cr(CO)₅] ethylenediamine monosolvate

Bis[(4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane)potassium(+)] pentacarbonylchromate(2−) ethylenediamine monosolvate, [K(C₁₈H₃₆N₂O₆)]₂[Cr(CO)₅]·C₂H₈N₂, was obtained from the reaction between K₃Cd₂Sb₂ and Cr(CO)₆ in ethylenediamine in the presence of the macrocyclic 2,2,2-crypt ligand. The structure provides the first crystallographic characterization of the pentacoordinated [Cr(CO)₅]²⁻ dianion. The central Cr^III atom is coordinated by five carbonyl ligands in a distorted trigonal–bipyramidal geometry. The distribution of the Cr—C bond lengths indicates a greater degree of back bonding from Cr^III to the equatorial carbonyl ligands compared with the axial carbonyl ligands.