Ambident nitrogen and oxygen ligands of the type tris(pyrazolyl)methanesulfonate: An “IR criterion” for the assignment of the coordination mode

The IR spectra of a series of metal complexes with the ambident nitrogen and oxygen ligand tris(3-tert-butylpyrazolyl)methanesulfonate, TpmstBu, were measured in the range 4000–50 cm−1. The solid-state structure of Li(TpmstBu)·12C6H12 has been determined by X-ray analysis. MTpmstBu (M = Li, K, Tl), [TpmstBuNiX] (X = Cl, Br), [TpmstBuZnX] (X = Cl, Br, I, Et), [(TpmstBu)Co(HpztBu)X] (X = Cl, Br), [(TpmstBu)Zn(μ-OAc)(μ-OH)Zn(TpmstBu)] and [(TpmstBu)CuL] (L = CO, PPh3, CH3CN) were investigated in solid state (KBr pellet) and in solution (CH2Cl2) and a band assignment is proposed. It could be shown that the assignment of the coordination mode to either N,N,N, N,N,O or N,O is possible by using an “IR criterion” specifying the binding mode. A dynamic equilibrium between the N,N,N and N,N,O coordination mode is observed in CH2Cl2 solutions of all investigated cobalt, nickel, copper and zinc complexes.