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Un carcéplex calix[4]areno con cuatro sujetadores Rh2 4+
F Albert Cotton1, Peng Lei, Chun Lin
1Laboratory for Molecular Structure and Bonding, Department of Chemistry, P.O. Box 30012, Texas A&M University, College Station, Texas 77842-3012, USA. cotton@tamu.edu
Journal of the American Chemical Society
|February 5, 2004
Resumen
Los investigadores ensamblaron carcéplejos esferoidales estables mediante la vinculación de calix[4]arenas con unidades dimetales, atrapando moléculas o iones. Estas jaulas exhiben una notable estabilidad y permiten el intercambio de ligandos en el cristal, lo que demuestra una química dinámica huésped-invitado.
Área de la Ciencia:
- Química supramolecular de las moléculas.
- Coordinación Química de la Coordinación
- Ciencia de los materiales Ciencia de los materiales.
Sus antecedentes:
- Desarrollo de jaulas moleculares para la encapsulación de huéspedes.
- Utilizando calix[4]arenas como bloques de construcción para arquitecturas complejas.
- Explorando unidades unidas metal-metal en ensamblajes supramoleculares.
Objetivo del estudio:
- Para sintetizar y caracterizar nuevos carcéplejos esferoidales.
- Para investigar la encapsulación de huéspedes moleculares y iónicos.
- Para evaluar la estabilidad y las propiedades dinámicas de los carcéplejos.
Principales métodos:
- Montaje de carcéplexos mediante el enlace de calix[4]arenas con unidades de dirhodium.
- Caracterización mediante cristalografía de rayos X, RMN, IR y espectrometría de masas.
- Investigación del intercambio de ligandos axiales en cristales simples.
Principales resultados:
- Síntesis exitosa de un carcéplex de tetraetilamonio (1b) con iones de tetraetilamonio atrapados.
- Demostración de alta estabilidad y intercambio dinámico de ligandos axiales (acetonitrilo/agua) sin pérdida de cristalinidad.
- Caracterización de compuestos relacionados de dimetal-calixareno con unidades de dirodio y dimolibdeno.
Conclusiones:
- Los carcéplexos esferoidales se pueden construir robustamente a partir de calix[4]arenas y unidades dimetales.
- Los carceplexos exhiben una estabilidad significativa y entornos de huéspedes sintonizables.
- El intercambio de ligandos en el cristal destaca el potencial de los materiales supramoleculares dinámicos.
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02:38Electrophilic Addition to Alkynes: Halogenation
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Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
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01:20Criteria for Aromaticity and the Hückel 4n + 2 Rule
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01:13Five-Membered Heterocyclic Aromatic Compounds: Overview
Heterocyclic aromatic compounds are cyclic compounds that are aromatic and have one or more heteroatoms—atoms other than carbon, in the ring. Depending upon the number of atoms present in the ring, they can be either five or six-membered. Examples of five-membered heterocyclic aromatic compounds include pyrrole, furan, thiophene, and imidazole. Pyrrole consists of one nitrogen atom having one lone pair of electrons. Furan and thiophene have one oxygen and one sulfur heteroatom, respectively.
01:18Frost Circles for Different Conjugated Systems
The inscribed polygon method is consistent with Hückel’s 4n + 2 rule and helps to learn whether the given cyclic compound is aromatic or not. The compound is stable and aromatic if every bonding molecular orbital (MO) is completely filled with a pair of electrons. However, if the non-bonding or antibonding orbitals are filled with electrons, the compound is unstable and not aromatic. Consider the Frost circle diagrams for cycloalkenes containing 4 to 8 carbons.
01:18Aromatic Hydrocarbon Cations: Structural Overview
Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
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