The tetrameric, η5‐coordinated aluminum(I) compound [{Al(C5Me5)}4] (1) is stable at room temperature. It was prepared from AlCl and [Mg(C5Me5)2]. In this cluster, four Al atoms form a regular tetrahedron and the planes of the C5Me5 rings lie nearly parallel to the respective faces of the tetrahedron. (see also Highlight on p. 544).

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The first sandwich complex of an element from the third main group, the cation in 1, has been synthesized and characterized by spectroscopy and X‐ray crystallography (see picture). This cation is stabilized by π interactions, and the Cp* ligands are staggered.

Two face‐sharing Al4P4 cubes, which lack two P atoms at the corners—this is the (idealized) framework of the title compound in the crystal. According to calculations, the isomer with adamantane structure is less stable by 30 to 80 kJ mol−1. As a result of quantum mechanical calculations on the model [P4(CpAl)6], [P4(Cp*Al)6] can be characterized as an electron‐deficient compound that is stabilized by considerable ionic bonding contributions.

Eine bei Raumtemperatur stabile Aluminium(I)‐Verbindung ist das tetramere, η5‐koordinierte [{Al(C5Me5)}4] 1, das aus AlCl und [Mg(C5Me5)2] herstellbar ist. In diesem Cluster bilden vier Al‐Atome ein reguläres Tetraeder, und die Ebenen der C5Me5‐Ringe liegen nahezu parallel zur jeweils gegenüberliegenden Basisfläche des Tetraeders. Siehe auch Highlight auf S. 559.