Exhaustively Methylated Azacalix[4]arene:  Preparation, Conformation, and Crystal Structure with Exclusively CH/π-Controlled Crystal Architecture

Abstract

[structure: see text]. Described are the preparation, conformation, and crystal structure of exhaustively methylated azacalix[4]arene involving nitrogen atoms as bridging units. NMR and X-ray crystallographic analysis have demonstrated that this novel azacalix[4]arene adopts a 1,3-alternate conformation both in solution and in the solid state. The crystal structure has been characterized solely by intermolecular CH/pi interactions, by which the azacalix[4]arenes mutually interact with each other outside the cavity to furnish a two-dimensional network structure.

Azacalix[6]arene Hexamethyl Ether: Synthesis, Structure, and Selective Uptake of Carbon Dioxide in the Solid State

“…three aromatic rings point to almost the same direction due to the presence of the two sets of intramolecular bifurcated MeO···NH···OMe hydrogen bonds formed between the aromatic rings A and B, and between the rings B and C. As shown in Figure 4, the same type of intramolecular bifurcated MeO···NH···OMe hydrogen bonds were observed for linear trimer 8, [12] which adopted the almost coplanar arrangement of the three aromatic rings. Accordingly, azacalix [6]arene 2 can be viewed as a N(3)-bridged head-to-tail dimer of two planar trimer units 8.…”

“…Toluene, CH 2 Cl 2 , and DMF were refluxed over and then distilled from CaH 2 under Ar before use. Palladium bis(benzylideneacetone) ([PdA C H T U N G T R E N N U N G (dba) 2 ]), [24] calix [6]arene 3, [25] and compounds 4 [15] , 6 [16] , and 8 [12] were prepared according to the described procedure. Other chemicals were purchased from commercial suppliers and used as received.…”

“…[12] As shown in Figure 12 and Figure S6 in the Supporting Information, carbocyclic calix [6]arene 3 also retains a nonporous and nonsolvated crystal structure, which is characterized by a 1D chain structure established by intermolecular CH/O interactions (CH···O, 2.61 and 1268; C···O, 3.28 ) between the methoxy group of the aromatic ring C and that of ring B belonging to the nearest molecules. As anticipated from their densely-packed nonporous crystal structures, both azacalix [4]arene 1 and calix [6]arene 3 gave rise to almost no uptake of CO 2 even at 195 K, as shown in Figure 13 and Figure S7 in the Supporting Information.…”

“…To explore whether solid-state complexation by nitrogen-bridged calixarene analogues would be feasible or not, we have synthesized azacalix [6]arene hexa-A C H T U N G T R E N N U N G methyl ether 2 in the present study, because a larger macrocycle than our previously reported azacalix [4]arene 1 [12] is essential for gaining a deeper insight into the host-guest chemistry of this molecular system. Among a variety of solid-state complexation phenomena, solid-gas adsorption behavior of 2 has been investigated in this study because it is an old, but yet forefront research area for selective gas recognition, storage, and separation, coupled with the environmental and industrial demands.…”

Synthesis and Properties of the Emerging Azacalix[14]arenes

“…Thus, considerable synthetic efforts are now devoted to the derivatization of basic calixarene skeletons, and more recent developments include the preparation of analogues by replacing the methylenic bridges by heteroatoms to tune the size of the cavity and to improve their binding properties. [12][13][14][15][16][17][18][19][20] Among the heteracalixarenes, N(R)-bridged azacalix[4]arenes of type 2, also called aza [1 4 ]metacyclophanes, are an emerging class of macrocycles owing to the presence of the nitrogen bridges, which open new perspectives in molecular magnetism and in supramolecular chemistry as hosts. [15,21] Curiously, inclusion properties of macrocycles of type 2 remain poorly explored, as only one example was described in the literature (R 1 = Me for K + complexation).…”