Mechanochemical Synthesis of 3d Transition-Metal-1,2,4-Triazole Complexes as Precursors for Microwave-Assisted and Thermal Conversion to Coordination Polymers with a High Influence on the Dielectric Properties

The complexes [MCl2(TzH)(4)] (M=Mn (1), Fe (2); TzH=1,2,4-1H-triazole) and [ZnCl2(TzH)(2)] (3) have been obtained by mechanochemical reactions of the corresponding divalent metal chloride and 1,2,4-1H-triazole. They were successfully used as precursors for the formation of coordination polymers either by a microwave-assisted reaction or by thermal conversion. For manganese, the conversion directly yielded [MnCl(2)TzH] (4), whereas for the iron-containing precursor, [FeCl(2)TzH] (6), was formed via the intermediate coordination polymer [FeCl(TzH)(2)]Cl (5). For cobalt, the isotypic polymer [CoCl(TzH)(2)]Cl (7) was obtained, but exclusively by a microwave-induced reaction directly from CoCl2. The crystal structures were resolved from single crystals and powders. The dielectric properties were determined and revealed large differences in permittivity between the precursor complexes and the rigid chain-like coordination polymers. Whereas the monomeric complexes exhibit very different dielectric behaviour, depending on the transition metal, from low-k to high-k with the permittivity ranging from 4.3 to >100 for frequencies of up to 1000Hz, the coordination polymers and complexes with strong intermolecular interactions are all close to low-k materials with very low dielectric constants up to 50 degrees C. Therefore, the conversion procedures can be used to deliberately influence the dielectric properties from complex to polymer and for different 3d transition-metal ions.