Abstract
Crystals of a supra-molecular lithium complex with a calix[4]arene derivative, namely tetra-methano-llithium 5,11,17,23-tetra-tert-butyl-25,26,27-trihy-droxy-28-oxidocalix[4]arene methanol monosolvate, [Li(CH3OH)4](C44H55O4)·CH3OH or [Li(CH3OH)4]+·(calix[4]arene-)]·CH3OH (where calix[4]arene- represents a mono-anion species because of deprotonation of one H atom of the calixarene hy-droxy groups), were obtained from p-tert-butyl-calix[4]arene reacted with LiH in tetra-hydro-furan, followed by recrystallization from methanol. The asymmetric unit comprises one mono-anionic calixarene mol-ecule, one Li+ cation coordinated to four methanol mol-ecules, and one methanol mol-ecule included in the calixarene cavity. The calixarene mol-ecule maintains a cone conformation by intra-molecular hydrogen bonding between one phenoxide (-O-) and three pendent calixarene hy-droxy groups (-OH). The coordinated methanol mol-ecules around the metal cation play a significant role in forming the supra-molecular assembly. The crystal structure of this assembly is stabilized by three sets of inter-molecular inter-actions: (i) hydrogen bonds involving the -OH and -O- moieties of the calixarene mol-ecules, the -OH groups of the coordinated methanol mol-ecules, and the -OH group of the methanol mol-ecule included in the calixarene cavity; (ii) C-H⋯π inter-actions between the calixarene mol-ecules and/or the coordinated methanol mol-ecules; (iii) O-H⋯π inter-actions between the calixarene mol-ecule and the included methanol mol-ecule.
Highlights
Crystals of a supramolecular lithium complex with a calix[4]arene derivative, namely tetramethanollithium 5,11,17,23-tetra-tert-butyl-25,26,27-trihydroxy-28oxidocalix[4]arene methanol monosolvate, [Li(CH3OH)4](C44H55O4)ÁCH3OH or [Li(CH3OH)4]+Á(calix[4]areneÀ)]ÁCH3OH, were obtained from p-tert-butylcalix[4]arene reacted with LiH in tetrahydrofuran, followed by recrystallization from methanol
The crystal structure of this assembly is stabilized by three sets of intermolecular interactions: (i) hydrogen bonds involving the –OH and –OÀ moieties of the calixarene molecules, the –OH groups of the coordinated methanol molecules, and the –OH group of the methanol molecule included in the calixarene cavity; (ii) C—HÁ Á Á interactions between the calixarene molecules and/or the coordinated methanol molecules; (iii) O— HÁ Á Á interactions between the calixarene molecule and the included methanol molecule
In the majority of cases, the alkali metal complexes of p-tert-butylcalix[4]arene in the solid state show direct coordination of the metal ions to the oxygen atoms belonging to the calixarene hydroxy groups at the lower rim, with the resulting crystal structures stabilized by weak interactions with the lattice solvent molecules
Summary
Calixarenes are synthetic macrocyclic compounds that are composed of phenol rings, linked with methylene groups at linking positions (Gutsche, 1998) They are versatile molecules for the inclusion of organic and/or inorganic compounds into their flexible cavities and for the coordination of organic/metal ions in molecular recognition phenomena and host–guest chemistry (Vicens & Bohmer, 1991). In the majority of cases, the alkali metal complexes of p-tert-butylcalix[4]arene in the solid state show direct coordination of the metal ions to the oxygen atoms belonging to the calixarene hydroxy groups at the lower rim, with the resulting crystal structures stabilized by weak interactions with the lattice solvent molecules. We report a different type of Li complex with p-tert-butylcalix[4]arene, in which no direct coordination of the metal to the oxygen atoms of the calixarene hydroxy groups takes place. The lithium cation is instead surrounded by four methanol solvent molecules, which are in turn connected to the host molecule via a series of hydrogen bonds, playing a significant role in the formation of the supramolecular assembly
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