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Characterization of Oligomers of AlCl: Al–Cl versus Al–Al Bonding
Author(s) -
Himmel HansJörg
Publication year - 2005
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200401016
Subject(s) - chemistry , trimer , dimer , matrix isolation , crystallography , tetramer , gibbs free energy , enthalpy , raman spectroscopy , hydrogen bond , monomer , computational chemistry , molecule , thermodynamics , organic chemistry , polymer , physics , optics , enzyme
Oligomers of AlCl have been characterized. By using the matrix isolation technique, the dimer Al 2 Cl 2 , which exhibits a D 2 h ‐symmetric ring structure, was generated in significant quantities and analyzed by its IR and Raman spectra in combination with quantum chemical calculations. The structures of the trimer and tetramer have also been evaluated. A surprising result is that the minimum energy structure of the trimer ( C s symmetry) features direct Al–Al bonds, two terminal Al–Cl bonds, and one bridging Cl atom. A weak, isotopically structured IR band can be assigned to the antisymmetric ν (Al–Cl t ) mode of this trimer (Cl t denotes a terminal Cl atom). The enthalpy change for each of the oligomerization steps has been calculated. For the dimerization of AlCl to give Al 2 Cl 2 , the Gibbs energy change was calculated as a function of temperature at different pressures. It turns out that neither the Al 2 Cl 2 dimer nor any higher oligomers are present in significant quantities in the gas phase, at least under the conditions of the experiments. The thermodynamic properties show that matrix isolation represents the optimal method of generating and characterizing these species. On the basis of the experimental results the barrier for dimerization of AlCl should be next to zero. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)