Crystal Structures of Uranyl Ion Complexes of Tetrahydroxy[3.1.3.1]metacyclophane (Homocalix[4]arene)

Abstract

The first crystal structures of complexes of tetrahydroxy-[3.1.3.1]metacyclophanes, also termed homocalix[4]-arenes, are reported. In the two uranyl ion complexes obtained, with different para-substituents, the complex core is analogous to that in tetrahomodioxacalix[4]arene complexes, with the cation in a tetra-phenoxide, distorted square-planar environment. The packing in one of these complexes comprises two different arrangements, one of them being a columnar stacking of complex molecules with sandwiched triethylammonium counter-ions hydrogen bonded to one complex and held by cation -p and CH -p interactions within the cavity of the other neighbouring one.

Supramolecular assemblages from uranyl complexes of calixarenes and potassium complexes of 18-crown-6 or dibenzo-18-crown-6

“…The dianionic uranyl complex moiety [UO 2 (L 1 )] 2À in compound 1 is analogous to that previously determined with this macrocycle in the presence of triethylamine [5]. The uranyl ion is located at the centre of the calixarene in the cone conformation and is bound to the four phenoxide groups with an average U-O bond length of 2.274(5) Å (tetragonal bipyramidal or distorted octahedral uranium environment).…”

Calixarene Complexes of Anion-bridged Oligouranyl Species

“…The independent uranium atom, in its equatorial plane, is a five-coordinate UO 5 array, cis-OZUZO ranging rather widely between 61.6(3) and 82.8(4)8 (Table II). One of the sites is occupied by the DMSO oxygen O(0), the others by a pair of adjacent phenoxy-oxygens O (11,21) of the calixarene ligand, O(21) bridging also to a symmetry-related uranium. The form of the ligand is that of a rather flattened cone with considerable variation in the tilt of the phenyl rings towards the mean plane; its exact protonation state is uncertain, the precision of the determination not permitting meaningful distinction between the phenoxy CZO distances, which range between 1.38 (2) Two uranyl complexes of p-t-Bu-calix [6] [22].…”

“…Focusing in particular on the 'parent' macrocycles, that is those that are unsubstituted at the phenolic rim, a particularly broadly investigated family is that of the uranyl-calixarene complexes [2,3]. Examples span ring sizes from calix [4]arene [4] to calix [12]arene [5], and also include thiacalixarenes [4], homooxacalixarenes [6 -16], homoazacalixarenes [17 -20] and homocalixarenes [21]. One attraction of the uranyl complexes in this context is that they are typically more resistant to hydrolysis when dissolved in noncoordinating solvents under ambient conditions than the analogous lanthanide or s-block metal complexes.…”

Synthesis of Azacalixarenes and Development of Their Properties

“…In each DMF inclusion, there is a clear C-H∙∙∙π interaction between the two hydrogens of the N -Me group of DMF and the two aromatic rings ( Figure 13 ); the DMF molecule is encapsulated in the cavity from the bulkier N , N -dimethyl group rather than from the -CHO side. C-H∙∙∙π interaction is a type of weak hydrogen bonding between C-H and π electrons, which is also shown in some of the inclusion compounds of calix[n]arenes [ 79 , 80 , 81 , 82 , 83 ]. A search of the CSD crystal structure database shows that the C-H∙∙∙π non-bond distance averages 291 pm, and analysis of the protein database shows that the most frequent distance between the C and π planes is 370–380 pm [ 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 ].…”