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.

The transition metal squarates M(C4O4) · 4 H2O (M2+ = Mn2+, Fe2+, Co2+. Ni2+, and Zn2+) are isotypic. They crystallize monoclinically, space group Ce-Cf, and consist of one-dimensional chain molecules[xxx]with the chain axes alternatively in direction [110] and [110]. The transition metal is octahedrally coordinated by two oxygen atoms of two C4O42- -anions in rrarcs-position and 4 water molecules. Neighbouring chains are interlinked by hydrogen bonds. The distance between the planes of the parallel C4-rings of neighbouring chains is similar to the layer distance in graphite.

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The first AlI halide that can be manipulated at room temperature, AlBr‐NEt3, is obtained by coconden‐sation of AlBr, NEt3, and toluene as yellow crystals and is stable to disproportionation up to about 95°C. In the crystal four Al atoms form a square, and the Br and NEt3 ligands alternate above and below this plane (shown on the right).