Inverse Aggregation Behavior of Alkali-Metal Triazenides

Higher aggregated alkali-metal compounds are usually obtained
with increasing radius of the metal. Alkali-metal salts derived from
the sterically crowded triazenido ligand Tph2N3H [Tph = C6H3-2,6-(C6H2-2,4,6-iPr3)2] do not obey this principle. Interestingly, these
compounds show inverse aggregation behavior in the solid state: 
the potassium and cesium salts crystallize as discrete monomers
in which the cations interact with flanking arene rings of the
diaryltriazenido ligands, whereas the lithium derivative is dimeric
with a more conventional heteroatom-bridged structure.