{μ‐PbSe}: A Heavy CO Homologue as an Unexpected Ligand

Reactions of [K(18‐crown‐6)] 2 [Pb 2 Se 3 ] and [K([2.2.2]crypt)] 2 [Pb 2 Se 3 ] with [Rh(PPh 3 ) 3 Cl] in en (ethane‐1,2‐diamine) afforded ionic compounds with [Rh 3 (PPh 3 ) 6 (μ 3 ‐Se) 2 ] − and [Rh 3 (CN) 2 (PPh 3 ) 4 (μ 3 ‐Se) 2 (μ‐PbSe)] 3− anions, respectively. The latter contains a PbSe ligand, a rather uncommon homologue of CO that acts as a μ‐bridge between two Rh atoms. Quantum chemical calculations yield a significantly higher bond energy for PbSe than for CO, since the size of the ligand orbitals better matches the comparably rigid Rh‐Se‐Rh angles and the resulting Rh⋅⋅⋅Rh distance. To rationalize the bent coordination of the ligand, orbitals with significant ligand contributions and their dependence on the bonding angle were investigated in detail.