Metal complexes of 3-carboxyethyl substituted trispyrazolylborates: interactions with the ester carbonyl oxygens

Abstract

The water molecules in complexes [Tp^CO₂Et,MeM(H₂O)₃]⁺ where M = Ni, Co, Mn, or Cu(II) are easily displaced by neutral bidentate ligands, L to produce species of the type [Tp^CO₂Et,MeM(L)H₂O]⁺. Attempted deprotonation of the water molecules in the parent complexes gives rise to rearrangement products for M = Ni, Co and Mn but gives isolable dinuclear hydroxo-bridged species for Zn and Cu. A number of interesting secondary interactions between the H-bond accepting [Tp^CO₂Et,Me] group and the other ligands in the metal coordination sphere are revealed by X-ray crystallography. The ester carbonyl CO stretching frequency of the ligand in the IR is seen to be diagnostic of the type of interaction (i.e. nonbonded, H-bonded or weakly complexed, and strongly complexed) between it and the cation, and can be used to provide valuable information in the absence of X-ray crystal structures.