The nature of the AuI ... AuI interactions between cationic [AuL2]+ complexes in the solid state

The interaction energy of a [Au{C(NHMe)(2)}(2)](+)center dot center dot center dot[Au{C(NHMe)(2)}(2)](+) dimer is investigated using the MP2 method and the LANL2DZ basis set when isolated or embedded in ionic an [Au{C(NHMe)(2)}(2)](2)anion(2) aggregate, a good model for the environment that these dimers feel in ionic crystals. A repulsive interaction energy is obtained when the dimer is isolated. However, it is possible to find short Au-I center dot center dot center dot Au-I separations in [Au{C(NHMe)(2)}(2)](2)anion(2) aggregates, because in these aggregates the sum of the cation...anion interactions overweight the sum of the cation... cation plus anion...anion interactions. This explains why short Au-I center dot center dot center dot Au-I separations are found in ionic crystals. The Au-I center dot center dot center dot Au-I interaction found in [Au{C(NHMe)(2)}(2)](2) anion(2) aggregates shows the same features observed in energetically stable dimers presenting Au-I center dot center dot center dot Au-I bonds. This makes appropriate to use the name counterion-mediated bonds for the Au-I center dot center dot center dot Au-I interactions found in [Au{C(NHMe)(2)}(2)](2) anion(2) aggregates and ionic crystals.