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Calculated Enthalpies for Dimerisation of Binary, Unsaturated, Main‐Group Element Hydrides as a Means to Analyse Their Potential for Multiple Bonding
Author(s) -
Himmel HansJörg
Publication year - 2003
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.200200637
Subject(s) - chemistry , main group element , ring strain , enthalpy , group (periodic table) , monomer , ethylene , computational chemistry , crystallography , cycloaddition , ab initio , ring (chemistry) , transition metal , organic chemistry , thermodynamics , catalysis , physics , polymer
Herein, the dimerisation of subvalent, binary, main‐group element hydrides with the potential for multiple bonding is studied using both hybrid DFT (B3LYP) and ab initio [MP2 and CCSD(T)] methods. The [2+2] cycloaddition is an important and characteristic reaction of derivatives of ethylene. A comparison of dimerisation reactions for several compounds with the potential for multiple bonding should, therefore, shed light on the properties of these species. Our study includes the hydrides E 2 H 2 (E = B, Al, Ga, N P or As), E 2 H 4 (E = C, Si or Ge) and ENH 4 (E = B, Al or Ga) and their dimers. Several isomeric forms of the monomers and dimers have to be considered. The trends within a group and a period are established and the factors responsible for them are discussed. It turns out that, generally, the enthalpies for dimerisation increase for heavier homologues, reflecting that the most important factor is the reduced strength of the E−E bonds in the monomers prior to dimerisation and, to some degree, also the reduced ring strain in the cyclic dimers. The exceptions are the dimerisations of B 2 H 2 and Al 2 H 2 , both of which lead to the tetrahedral E 4 H 4 species (E = B or Al). Dimerisation of Al 2 H 2 is associated with a smaller enthalpy than that for the dimerisation of B 2 H 2 . Comparisons and analyses are made complicated because of the changes in the structures of the isomeric global minima between homologues. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)