Stabilisation of Li(0)-Li(0) bond by normal and mesoionic carbenes and electride characteristics of the complexes

Abstract

Density functional theory (DFT) has been used to study the structure, stability, and bonding in the Li2L2 complexes containing Li(0)-Li(0) bond using both normal and mesoionic carbenes (MICs) as binding ligands (L) with Li2 molecule. The geometries and the nature of bonding of Li2(SNHCMe)2 and Li2(cAACMe)2 normal carbene complexes and Li2(MIC1)2 and Li2(MIC2)2 mesoionic carbene complexes have been compared with the previously reported Li2(NHC)2 normal carbene complex. The stability of the designed complexes is determined by positive Gibbs’ free energy changes (ΔG) towards the dissociation of the complexes into different fragments. Both normal and mesoionic carbenes stabilise the Li2 moiety and both the types of complexes are almost equally stable. From the natural bond orbital (NBO) analysis and the atoms in molecule (AIM) analysis, it is shown that two Li atoms are bonded by a single covalent bond with the oxidation state of zero on each Li. Again, the electron density analysis confirmed that each Li-Li bond has a non-nuclear attractor (NNA) at the middle of the bonds and the values of Laplacian of electron density (∇2ρ(r)) are negative therein. Both the types of complexes show electride characteristics. The reactivity descriptors of all the studied complexes have been analyzed.