Crystal packing, aromatic crystals

Their research has focused on examining the effect of substitution on the aromatic ring in the crystal state. Their results show that different substitution leads to different structures being formed in the crystal state. They conclude that even weak intermolecular interactions such as C-H-O hydrogen bonds can be used to control crystal packing within glycoluril systems. 

Figure 6.5. The four basic aromatic crystal packings,...

Using the metalloradical reactivity of the Rh(II)OEP (OEP = 2,3,7,8,12,13,17,18-octaethylphorphynato) dimer, the preparation of silyl rhodium complexes was achieved by the hydrogen elimination reaction with silanes I R SiH (R = R = Et, Ph R = Me, R = Ph, OEt). The Rh—Si bond length of 2.32(1) A, found when R = Et, is comparable to those in other Rh(III) complexes (Table 11). The crystal packing indicates that all the ethyl groups on the porphyrin periphery are directed toward the silyl group. Consequently, the aromatic part of one complex molecule is in contact with the aromatic part of the next molecule and the aliphatic part is in contact with the aliphatic part of the next molecule204. 

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