Structural and thermodynamic properties of molecular complexes of aluminum and gallium trihalides with bifunctional donor pyrazine: decisive role of Lewis acidity in 1D polymer formation

URN zum Zitieren dieses Dokuments:: urn:nbn:de:bvb:355-epub-342331
DOI zum Zitieren dieses Dokuments:: 10.5283/epub.34233

Sevastianova, T. N.

; Bodensteiner, Michael ; Lisovenko, A. S.

; Davydova, E. I.

; Scheer, Manfred

; ;

;

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Veröffentlichungsdatum dieses Volltextes: 04 Aug 2016 08:44

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Solid state structures of group 13 metal halide complexes with pyrazine (pyz) of 2 : 1 and 1 : 1 composition have been established by X-ray structural analysis. Complexes of 2 : 1 composition adopt molecular structures MX3 center dot pyz center dot MX3 with tetrahedral geometry of group 13 metals. Complexes of AlBr3 and GaCl3 of 1 : 1 composition are 1D polymers (MX3 center dot pyz)(infinity) with trigonal bipyramidal geometry of the group 13 metal, while the weaker Lewis acid GaI3 forms the monomeric molecular complex GaI3 center dot pyz, which is isostructural to its pyridine analog GaI3 center dot py. Tensimetry studies of vaporization and thermal dissociation of AlBr3 center dot pyz and AlBr3 center dot pyz center dot AlBr3 complexes have been carried out using the static method with a glass membrane null-manometer. Thermodynamic characteristics of vaporization and equilibrium gas phase dissociation of the AlBr3 center dot pyz complex have been determined. Comprehensive theoretical studies of (MX3)(n)center dot(pyz)(m) complexes (M = Al, Ga; X = Cl, Br, I; n = 1, 2; m = 1-3) have been carried out at the B3LYP/TZVP level of theory. Donor-acceptor bond energies were obtained taking into account reorganization energies of the fragments. Computational data indicate that the formation of (MX3 center dot pyz)(infinity) polymers with coordination number 5 is only slightly more energetically favorable than the formation of molecular complexes of type MX3 center dot pyz for X = Cl, Br. It is expected that on melting (MX3 center dot pyz)(infinity) polymers dissociate into individual MX3 center dot pyz molecules. This dovetails with low melting enthalpies of the (MX3 center dot pyz)(infinity) complexes. Polymer stability decreases in the order AlCl3 > AlBr3 > GaCl3 > AlI3 > GaBr3 > GaI3. For MI3 center dot pyz complexes computations predict that the monomeric structure motif is more energetically favorable compared to the catena polymer. These theoretical predictions agree well with the experimentally observed monomeric complex GaI3 center dot pyz in the solid state. Thus, the Lewis acidity of the group 13 halides may play a decisive role in the formation of 1D polymeric networks.

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