First Homoleptic Complexes of the Tridentate Pyridine‐2,6‐ditetrazolate Ligand

The synthesis and spectroscopic characterisation of a series of homoleptic complexes of the tridentate pyridine-2,6-di(5-tetrazolate) ligand (pydtz2) with CoII, NiII, CuII and ZnII are reported. Single-crystal XRD data reveals the formation of octahedrally configured complexes [M(pydtz)2]2 for M = Zn or [M(Hpydtz)(pydtz)] for M = Co or Ni, whereas for M = Cu a polymeric structure [Cu(pydtz)(EtOH)]n crystallised. In the latter, alternate short and long Cu center dot center dot center dot Cu distances were found. Magnetic measurements and electron paramagnetic resonance (EPR) spectroscopy reveal noncoupled S = 1/2 CuII ions for [Cu(pydtz)(EtOH)]n, S = 1/2 low-spin configuration for the CoII complex and an S = 1 ground state for the NiII derivative. At T < 16 K the latter shows anomalies that resemble those of single-ion molecular magnets. The ligand strength of pydtz2 is markedly higher than that of the bioisosteric pyridine-2,6-dicarboxylate (pydic2) ligand and is very similar to that of the well-established 2,2:6,2-terpyridine (terpy) ligand as revealed by the ligand field bands of the Co, Ni and Cu complexes and the magnetism of the Co and Ni derivatives. Solution electrochemical investigations suggest that essentially ligand-centred reduction at rather negative potentials and metal-centred oxidation processes occur.