By using diphosphane (P 2 H 4 ) as the source of phosphorus N. Korber and co-workers have succeeded in isolating a compound that contains a 6p aromatic P 4 2À unit, shown, which was missing in the series of E 4 2À ions of group 15. For more information, see the Communication on the following pages.

Dissolving the ternary material K 6 Rb 6 Si 17 together with chelating ligands such as 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane), dibenzo-18-crown-6 (2,3,11,12-dibenzo-1,4,7,10,13,16-hexaoxacyclooctadecane) ]Rb 3 Si 9 ·4NH 3 . Single-crystal X-ray diffraction analysis reveals the presence of Si 9 4-anions, the existence of which in solution has been a matter of discussion until now. In both compounds, the Si 9 4-cages display slightly

It's detected! The existence of the prototypical Zintl ions Tt44− (Tt=Group 14 element), which are isoelectronic to the P4 molecule, used to be confined to the solid state. Recently, circumstantial evidence for a solution chemistry in liquid ammonia emerged. Direct spectroscopic observation of the dissolved anions has now been achieved. In the case of Si44−, this is the first solution detection of any homoatomic silicide.

The incongruent solvation of M(I)4P6 species (M(I) = K, Rb, Cs) in liquid ammonia leads to a broad variety of polyphosphides such as P7(3-), P11(3-), and the putatively aromatic P4(2-) and P5(-), which we investigated by using NMR spectroscopy and single-crystal X-ray structure analysis. The structures of Cs2P4 x 2 NH3, (K@[18]crown-6)3K3(P7)2 x 10 NH3, Rb3P7 x 7 NH3, and (Rb@[18]crown-6)3P7 x 6 NH3 are discussed and compared. The electron localization function ELF is used in a comparison of the chemical bonding of various phosphorus species. The variances of the basin populations provide a well-established measure for electron delocalization and therefore aromaticity. While comparable variance is calculated for P4(2-) and P5(-) it is observed in the lone pairs rather than in the basin populations of the bonds as in the prototypical aromatic hydrocarbons such as benzene or the cyclopentadienide anion. For this behavior, the term "lone pair aromaticity" is proposed.

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