X‐Ray Crystallographic Investigations of an Azacryptand and its Bis‐Protonated Salt: Interactions of Acyclic Water Trimer and C‐H…π Interactions in T‐shaped Benzene Dimer

Crystal structures of octaaminocryptand L, (1,4,11,14,17,24,29,36‐octa azapentacyclo[12.12.12.2.6,92.19,22231,34]tetratetraconta‐6(43), 7,9(44),19(41),20,22(42),31(39),32,34(40)‐nonaene, N(CH2CH2NHCH2‐p‐xylyl‐CH2NHCH2CH2)3N) with half a molecule of water and its bisprotonated form LH2 2+ · 2ClO4¯ · 3H2O, 1 have been reported. Crystal structure of salt 1 provided an evidence of a water trimer‐perchlorate hybride cluster in the crystal lattice. Water trimer isolated in the lattice is acyclic and hydrogen bonded to the perchlorate from both sides. Crystal structures of L and 1 provides a unique case to examine the relative strength of benzene dimer between centroid vs. edge using the observed T‐shaped arrangement of phenyl planes. The maximum stabilization is found near the centroid of the phenyl plane by computing the geometries derived from crystal structures. This result was further substantiated by ab initio alculations at MP2/aug‐cc‐pVTZ level showing that the centroid interaction is preferred by ∼0.7 kcal/mol. Furthermore, the bisprotonated form of L, 1 also shows shortest intramolecular CH/π contact (2.50 Å) observed in the solid state. The inferences derived from this study should be useful in refining empirical potentials for modeling the interactions of aromatic susbstrates in biomolecules and supramolecular assemblies.