The crystal structures of Rb[2.2.2crypt] 2 Mn 2 (CO) 8 ⋅ 4NH 3 and K[18crown‐6] 2 K 2 W 2 (CO) 8 ⋅ 14NH 3 are reported, containing the first homoleptic dinuclear carbonyl metalates featuring metal−metal double bonds. Mn 2 (CO) 8 2− and W 2 (CO) 8 4− are isostructural and isoelectronic to the elusive Fe 2 (CO) 8 . Quantum chemical calculations and QTAIM analysis confirm the metallic bonding character, as well as differences in terminal and bridging carbonyl ligands.
Witzmann et al. (Mon,) studied this question.