Solvent-mediated intermolecular bonds: cation-cation and anion-anion interactions in solution showing the signature of chemical bonds

摘要

In this work we present the principles that govern the presence in solution of short distance cation-cation and anion-anion interactions having the signature of a bond (for instance, luminescence, caused by shifts in the electronic spectra). We will show here that these bond features in solution can be found when energetically stable cation(2)solvent(n) and anion(2)solvent(n) aggregates are present. The stability of these aggregates comes from the ion-solvent interactions, whose sum overcomes the repulsion between ions of the same sign. Their electronic properties are due to the short ion-ion distance, which induces a non-negligible ion-ion orbital overlap. Such overlap gives rise to the same orbital energy diagram found in energetically stable dimers.We have illustrated such behavior for the acetone solutions of [Au(C(NHMe)(2))(2)](+) and of TCNE- in dichloromethane, where energetically stable ([Au(C(NHMe)(2))(2)](+))(2)acetone(4) and (TCNE-)(2)dichloromethane(6) aggregates have been identified (although their stability is small). The Au-Au distance in the ([Au(C(NHMe)(2))(2)](+))(2)acetone(4) aggregate is 3.833 angstrom and its electronic spectrum is shifted respect to that for the isolated monomers. In the (TCNE-)(2)dichloromethane(6) aggregates the interaction energy is very small and the TCNE--TCNE- distance is much larger (4.760 angstrom). As a consequence, no shifts in the electronic spectra are found. (c) 2005 Elsevier B.V. All rights reserved.