Guest-driven unusual conformations in two calix[6]arene solvates and a new calix[8]arene

Author:

Martins Felipe Terra12,da Silva Maia Angélica Faleiros2,dos Santos Fernando Machado1,Alvarenga Meiry Edivirges1,Ribeiro Leandro1,da Silva Neto Leonardo2,de Fátima Ângelo2

Affiliation:

1. Instituto de Química , Universidade Federal de Goiás, Campus Samambaia, CP 131 , Goiânia, GO 74001-970 , Brazil

2. Grupo de Estudos em Química Orgânica e Biológica (GEQOB), Departamento de Química , Instituto de Ciências Exatas , Universidade Federal de Minas Gerais , Av. Pres. Antônio Carlos, 6627 , Belo Horizonte, MG 31270-901 , Brazil

Abstract

Abstract Unusual conformations have been found in a new calix[8]arene and in new solvates of two known calix[6]arenes. The chair-like conformation with 2/m point group symmetry was found for the first time in the dimethylformamide (DMF) disolvate of the basic calix[6]arene (1) without substituents in the lower and upper rims. Such symmetry is driven by the guest geometry allowing for two equivalent hydrogen bonding patterns in the chair seat. This avoids cone distortion found in the other chair-like conformers, although they have energies lower than that of new symmetrical conformer. The molecular conformation of hexa(carboxymethoxy)calix[6]arene (2) is also described as a dimethylsulfoxide (DMSO) pentasolvate. Its conformation can be described as a 1,3,5-closed cone with three alternate phenyl rings inclined inwards to the cone, thereby closing the cone entrance. Such a conformation also suggests five acid groups are pointed towards the same side of the calyx base and are able to bind metal ions or basic compounds in the lower rim, while inclusion of guests into the cone cavity is hindered. Both inclusion and cooperative acid binding/coordination abilities are still more hindered in the lowest energy 1,2,3-alternate cone conformer of 2. The role of the solvent in avoiding cone distortion was highlighted by inspecting the conformations of 5,11,17,23,29,35,41,47-octanitro-49,50,51,52,53,54,55,56-octa-n-butoxycalix[8]arene (3) and the known nitro analogues having methyl instead of n-butyl groups. Cone distortion is found in the non-solvated crystal form of 3, while non-classical hydrogen bonds with tetrahydrofuran preclude this in the literature analogue.

Publisher

Walter de Gruyter GmbH

Subject

Inorganic Chemistry,Condensed Matter Physics,General Materials Science

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