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Abstract Sandwich-type clusters with the planar fragment containing a heterometallic sheet have remained elusive. In this work, we introduce the [K(2,2,2-crypt)] 4 {(Ge 9 ) 2 [ η 6 -Ge(PdPPh 3 ) 3 ]} complex that contains a heterometallic sandwich fragment. The title compound is structurally characterized by means of single-crystal X-ray diffraction, which reveals the presence of an unusual heteroatomic metal planar fragment Ge@Pd 3 . The planar fragment contains a rare formal zerovalent germanium core and a peculiar bonding mode of sp 2 -Ge@(PdPPh 3 ) 3 trigonal planar structure, whereas the nonagermanide fragments act as capping ligands. The chemical bonding pattern of the planar fragment consists of three 2c-2e Pd-Ge σ-bonds attaching Pd atoms to the core Ge atom, while the binding between the planar fragment and the aromatic Ge 9 ligands is provided by six 2c-2e Pd-Ge σ-bonds and two delocalized 4c-2e σ-bonds. The synthesized cluster represents a rare example of a sandwich compound with the heteroatomic metal planar fragment and inorganic aromatic capping ligands. 

In this work, we report a dimeric cluster anion, {[CuGe 9 Mes] 2 } 4− , which was isolated as the [K(2,2,2-crypt)] + salt and characterized by using single-crystal X-ray diffraction and ESI mass spectroscopy. The title cluster represents the first locally σ-antiaromatic compound in the solid state, as well as the first heteroatomic antiaromatic compound. 

Antiaromaticity, as introduced in 1965, usually refers to monocyclic systems with 4nπ electrons. This concept was extended to all‐metal molecules after the observation of Li₃Al₄⁻in the gas phase. However, the solid‐phase counterparts have not been documented to date. Herein, we describe a series of all‐metal antiaromatic anions, [Ln(η⁴‐Sb₄)₃]³⁻(Ln=La, Y, Ho, Er, Lu), which were isolated as the K([2.2.2]crypt) salts and identified by single‐crystal X‐ray diffraction. Based on the results obtained from the chemical bonding analysis, multicenter indices, and the electron‐counting rule, we conclude that the core [Ln(η⁴‐Sb₄)₃]³⁻fragment of the crystal has three locally π‐antiaromatic Sb₄fragments. This complex represents the first locally π‐antiaromatic all‐metal system in the solid state, which is stabilized by interactions of the three π‐antiaromatic units with the central metal atom.