Weak carbon-hydrogen-nitrogen interactions affect the heterocyclic ligand bonding modes in barium complexes containing η2-tetrazolato and η2-pentazolato ligands

Treatment of Ba[N(SiMe 3 ) 2 ] 2 (THF) 2 with 2 equiv of dimethylaminotetrazole or diisopropylaminotetrazole and 1 equiv of 18-crown-6 afforded Ba[CN4(NMe2)] 2 (18-crown-6) (87%) and Ba[CN 4 (NiPr 2 )] 2 -(18-crown-6) (79%) as colorless crystalline solids. Ba[CN 4 (NMe 2 )] 2 -(18-crown-6) contains two 1,2-η 2 -tetrazolato ligands and one η 6 -18-crown-6 ligand. The molecular structure of Ba[CN 4 (NiPr 2 )] 2 (18-crown-6) is similar to that of Ba[CN4(NMe2)]2(18-crown-6), except that the tetrazolato ligands exhibit the isomeric 2,3-η 2 -coordination mode and the tetrazolato ligand CN 4 cores are bent significantly toward the 18-crown-6 ligands. Molecular orbital calculations were carried out on the model complexes Ba(azolate)2(18-crown-6) (azolate = 1,2-η 2 -CHN 4 , 2,3-η 2 -CHN 4 , and η 2 -N 5 ) and demonstrate that the ligand coordination modes are influenced by intramolecular interactions between filled nitrogen orbitals on the azolato ligands and empty C-H σ* orbitals on the 18-crown-6 ligands.