Hydrogen-bonding interactions in monomeric dimethylcuprates. A theoretical study

The hydrogen-bonding interactions between dimethylcuprate anions of monomeric lithium dimethylcuprate solvates and C-H bonds of molecules which solvate lithium cation were studied. The NBO analysis and analysis of internuclear distances are used to reveal these interactions in B3LYP and MP2 calculated monomeric lithium dimethylcuprates (LDMCs), and in the published X-ray structures of monomeric dimethylcuprates. The relevance of QTAIM analysis for the description of hydrogen-bonding interactions in LDMCs is evaluated. Different types of hydrogen bonds (HBs), e.g. C-H···Cu and C-H···C HBs as well as C-H···H dihydrogen bonds are revealed by the calculations of monomeric lithium dimethylcuprates with the cation surrounded by solvent molecules. All of these HB types were found to exist in the solid state between dimethylcuprate anion and C-H bonds of the solvent or ligand molecules. Multiple HBs of different types and strengths are simultaneously formed with dimethylcuprate anions in the monomeric cuprates studied. It is demonstrated that multiple hydrogen-bondings, accompanied by an unsymmetrical interaction of the dimethylcuprate anion with C-H bonds, can lead to impressive geometrical changes, including e.g. different C-Cu bond lengths in some “solvent-separated ion pairs”. In some monomeric cuprates the C-Cu-C unit of dimethylcuprate anion was found to bend even in the absence of Cu···Cu interactions.