Controlling the Conformation and Interplay of p‐Sulfonatocalix[6]arene as Lanthanide Crown Ether Complexes

Abstract

Control over the conformational flexibility of p-sulfonatocalix[6]arene in the solid state is possible in the presence of varied stoichiometric amounts of [18]crown-6 and selected lanthanide(III) chlorides. Complexes 1 and 2 have the calixarene in the elusive up-up double cone conformation, whilst complex 3 has the calixarene in the centrosymmetric up-down double partial cone conformation, whereby it acts as a divergent receptor. Complex 1 has a double molecular capsule arrangement which is composed of two p-sulfonatocalix[6]arenes shrouding two [18]crown-6 molecules, also with both coordinated and homoleptic aquated lanthanide ions around the hydrophilic sulfonate rims of the calixarenes. Complex 2 has a ferris wheel arrangement with one lanthanide metal centre coordinated to a sulfonate group and another coordinated to the crown ether whilst tethered to a sulfonate group of the calixarene. Complex 3 forms from a solution with large excess of [18]crown-6, and possesses a crown ether molecule in each of the partial cones and has homoleptic aquated lanthanide ions involved in a complicated hydrogen-bonding regime within the extended structure.

Supramolecular Assembly of <i>p</i>-Sulfonatothiacalix[6]arene Yttrium Complex Supported by Hydrogen Bonding, π–π Stacking, and S–π Interactions

“…It is suggested that the pseudo 'thiacalix [3]arene-like' cavities, like a small macrocyclic ring assembled each of three p-sulfonatophenol units, assemble through a combination of hydrogen bonding and hydrophobic interactions in aqueous media. In previous reports, 'up-up' double conical and 'up-down' double conical conformations possessing pseudocavities were observed [17]. Likewise, complex I adopts a similar 'up-down' double partial-cone conformations as those reported for metal complexes of p-sulfonatothia-and calix [6]arenes [15][16][17][47][48][49].…”

“…The inclusion of organic and/or inorganic compounds into their flexible cavities and the coordination of organic/metal ions in supramolecular chemistry have been reported [7][8][9]. In particular, water-soluble p-sulfonatocalix [n]arenes (n = 4−8) have attracted significant attention owing to several intriguing properties in both the solution and solid states [10][11][12][13][14][15][16][17][18][19][20][21]. Their functional and conformational characteristics lead to a macrocyclic biological mimic for interesting assembled architectures [22,23].…”

“…Water-soluble calix [4]arene 1 provides well-defined architectures, such as 'Sphere', 'Tubule', 'Russian-doll', 'Ferriswheel', and 'Helix' molecular assemblies, through the combination of metal cations and cyclic/acyclic-organic ligands [24][25][26][27]. In contrast, only a few structural investigations of alkali or lanthanide metal complexes with larger p-sulfonatocalix [6]arenes (2) have been reported [15][16][17]. In alkali metal complexes (Na, Rb, and Cs), the calixarene molecules adopt an 'up-down' double partialcone conformation that is composed of three 'up' sulfonate groups and three 'down' sulfonate groups of calixarene [15,16].…”

“…In alkali metal complexes (Na, Rb, and Cs), the calixarene molecules adopt an 'up-down' double partialcone conformation that is composed of three 'up' sulfonate groups and three 'down' sulfonate groups of calixarene [15,16]. In the conformational studies of lanthanide complexes of 2 published by Raston and co-workers [17], the conformers adopt an 'upup' double-cone conformation or 'up-down' double partial-cone conformation depending on the fusion of ligating crown ether molecules with metals, the number of guests, and the nature of the lanthanide metals. In addition, both molecules 1 and 2 also provide fascinating assemblies such as 'molecular-capsule' and 'Ferriswheel' arrangements, which are formed when these lanthanide crown ethers complex with 2.…”

Structural Versatility in Praseodymium Complexes of p-Sulfonatocalix[4]arene

“…17 Guest-induced conformational distortion can afford a bismolecular capsule arrangement, 18 and similar bis-capsules can be formed for SO 3 [6] and SO 3 [8] with 18-crown-6 and tetraphenylphosphonium guest species respectively, as parts of lanthanide metal complexes. 15,19 Considering the substantial number of complicated multicomponent supramolecular solid-state complexes reported for SO 3 [4] and the larger analogues, relatively few simple metal complexes of the SO 3 [4] (other than alkali metals and some formed in the absence of guest) have been reported. [20][21][22][23] Herein we report the formation of three metal complexes either with incorporation or exclusion of the metal salt anion.…”