Substituent Effects on Cooperativity Between Lithium Bonds

Substituent effects on cooperativity between lithium bond interactions in NCLiNCLiNCX and CNLiCNLiCNX complexes are reported, where X=H, F, Cl, Br, CN, NC, OH, NH2, and CH3. Molecular geometries and interaction energies of dyads and triads are investigated with the MP2 and single, double, and perturbative triple excitation coupled-cluster CCSD(T) methods. It is found that the intermolecular distances in the triads are always smaller than the corresponding values in the binary systems. That is, the two lithium-bonding interactions have a cooperative effect on each other. Evidently, the effect is larger in those complexes with shorter intermolecular distances than in those with the longest ones. The estimated values of cooperative energy E-coop are all negative with much larger E-coop in absolute value for the systems including electron donating groups (X=NH2, OH and CH3). The nature of lithium bond interactions of the complexes is analyzed using parameters derived from the quantum theory atoms in molecules methodology and energy decomposition analysis. It is revealed that electron density at the LiN and LiC critical points can be regarded as a good description to quantify the degree of cooperative effects in these systems. (c) 2013 Wiley Periodicals, Inc.