Mechanochemical and thermal formation of 1H-benzotriazole coordination polymers and complexes of 3d-transition metals with intriguing dielectric properties

Abstract

Liquid-assisted grinding (LAG) reactions have been successfully applied to achieve a series of complexes and coordination polymers based on divalent 3d-transition metal chlorides (TM chlorides) and the aromatic ligand 1H-benzotriazole (BtzH). The obtained substances were investigated via single crystal X-ray, powder X-ray determination and simultaneous DTA/TG analysis as model compounds for structural and chemical influences on their dielectric properties. Depending on the synthesis method, different constitutions and structures are observed. Two polymorphous forms of the 1D polymer ¹_∞[MnCl₂(BtzH)₂] (1 and 2) as well as the complexes [ZnCl₂(BtzH)₂]·BtzH (3) and [CoCl₂(BtzH)₂]·BtzH (4) have been obtained as phase-pure bulk substances via the mechanochemical LAG route, and even single crystals are available. For comparison, thermal reactions were also carried out and have led to the formation of the neutral complexes: [CoCl₂(BtzH)₂] (5) and [CoCl₂(BtzH)₄]·4BtzH (6), [ZnCl₂(BtzH)₂] (7) and the anionic complex BtzH₂[CoCl₃BtzH] (8). In addition, thermal treatment of 3 yields the benzotriazolium salt {(BtzH)₂H}Cl (9). The transition metal compounds were additionally analysed regarding their dielectric properties by frequency-dependent as well as temperature-dependent permittivity investigations. It is intriguing that compounds 1 and 3 show remarkably low dielectric constants and loss factors up to 50 °C highlighting them as potential “low-k materials”.