Structural Diversity in Alkali Metal Complexes of Sterically Demanding Carbazol-9-yl Ligands

The solid state structures of alkali metal complexes
of the 1,3,6,8-tetra-tert-butylcarbazol-9-yl (tBu4carb–) ligand
are compared. Lithium complex [tBu4carbLi]2 ([1]2) is a dimer
in the solid state featuring a planar LiNLiN rhomboid ring, with the
differing Li–N distances within the ring due to the effects
of σ- and π-interactions. Recrystallization of lithium,
sodium, and potassium complexes of the 1,3,6,8-tetra-tert-butylcarbazol-9-yl ligand from THF leads to the formation of tBu4carbLi­(THF)2 (1·2THF), tBu4carbNa­(THF)3 (2·3THF), and tBu4carbK­(THF)4 (3·4THF),
respectively, in the solid state. For these THF adducts, on proceeding
from lithium to sodium to potassium there is an increase in hapticity
of the binding of the carbazol-9-yl ligands to the metal cations,
mirroring the increasing ionic bonding character in these compounds.