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Abstract

The synthesis and spectroscopic characterisation of a series of heteroleptic complexes of the tridentate pyridine-2,6-di-(5-tetrazolate) (pydtz(2-)) with Co(II), Ni(II), Cu(II) and Zn(II) and pyridine (Py) and H2O as coligands is reported. Single crystal XRD data reveals the formation of octahedrally configured complexes [Co(pydtz)(H2O)(Py)(2)], [Co(pydtz)(H2O)(2)(Py)]2H(2)O, [Ni(pydtz)(Py)(3)]2Py, and [Zn(pydtz)(H2O)(Py)(2)]Py, and a markedly Jahn-Teller distorted octahedral structure for [Cu(pydtz)(H2O)(2)(Py)]. Magnetic measurements reveal a S = 3/2 high-spin configuration for the Co(II) complex [Co(pydtz)(H2O)(Py)(2)], an S = 1 ground state for the Ni(II) derivative and S = 1/2 Cu(II) ions for [Cu(pydtz)(H2O)(2)(Py)], the latter is supported by electron-paramagnetic-resonance spectroscopy. The crystalline materials are subject to severe corrosion as revealed by powder XRD and DSC-TG experiments. H2O and pyridine co-crystallisates and coligands are easily cleaved. At the same time DSC-TG reveal very high stability of the [M(pydtz)] fragments with exothermic decomposition at T > 300 degrees C. As a consequence, in pyridine solution in all cases the species [M(pydtz)(Py)(3)] are observed. Ultraviolet-visible light absorption spectroscopy reveals a strong ligand field procured by the pydtz(2-) ligand and electrochemical measurements suggest very strong sigma-donation but only weak -accepting abilities of pydtz(2-) compared to the isostructural terpy (2,2';6',2''-terpyridine) ligand.