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 ((t)Bu4carb(-)) ligand are compared. Lithium complex [(t)Bu4carbLi]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 (t)Bu4carbLi(THF)2 (1·2THF), (t)Bu4carbNa(THF)3 (2·3THF), and (t)Bu4carbK(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.