A tridentate bis(pyrazolyl) ligand binds to Cu(II), without using the pyrazole group: a very unusual coordination mode of the ligand Hbdmpb, 1,3-bis(3,5-dimethylpyrazol-1-yl)-2-butanoic acid

The ligand 1,3-bis(3,5-dimethylpyrazol-1-yl)-2-butanoic acid reacts with copper(II) nitrate in the presence of base, forming a mononuclear copper(II) complex. Very unusually, the pyrazole rings of the ligand do not coordinate to metal ions, instead being involved in strong intermolecular hydrogen bonds. The single crystal structures of the free ligand and the complex were solved.