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

Abstract

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 1∞ [MnCl2 TzH] (4), whereas for the iron-containing precursor, 1∞ [FeCl2 TzH] (6), was formed via the intermediate coordination polymer 1∞ [FeCl(TzH)2]Cl (5). For cobalt, the isotypic polymer 1∞ [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 1000 Hz, the coordination polymers and complexes with strong intermolecular interactions are all close to "low-k" materials with very low dielectric constants up to 50 °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.

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

“…S13 †) together with a slight frequency dependence for low frequencies. Altogether, the observed properties are in accordance with a recent study on TM-1,2,4-triazoles, 14 which also show low dielectric constants due to the intermolecular rigidity of these compounds based on hydrogen bonding and π-π-interactions, with the highest rigidity for the Zn-containing compounds.…”

“…In contrast to the direct formation of crystalline 1,2,4-1H-triazole-based metal complexes and coordination polymers from the mechanochemical reaction of the solids in a ball mill, 14 the dry milling of solid 1H-benzotriazole with the transition metal chlorides does not prove suitable but yields reactants or unknown phases only (see ESI, Table S1, Fig. S1-S3 †).…”

“…The compound is isotypic to the literature-known complex [ZnCl 2 (BtzH) 2 ] (7). 14 Crystal structure of [CoCl 2 (BtzH) 4 ]•4BtzH (6). The complex [CoCl 2 (BtzH) 4 ]•4BtzH (6) crystallises in the tetragonal crystal system in the space group P4/n with two formula units per unit cell.…”

“…Complexes and coordination polymers like [ZnCl 2 (TzH) 2 ] and 1 ∞ [MnCl 2 TzH] with strong intermolecular interactions show low-k-behaviour, whereas related compounds such as [MnCl 2 (TzH) 4 ] exhibit high-k values for the dielectric constant at room temperature. 14 Therefore, expansion of the π-system while retaining the arrangement of N-coordination sites seem a promising strategy to achieve further model compounds for a large variety of dielectric properties. 1H-Benzotriazole (BtzH) as well as its deprotonated form and its derivatives are common N-heterocyclic ligands by virtue of their flexibility due to different coordination and bridging modes.…”

Spin State Crossover, Vibrational, Computational, and Structural Studies of FeII 1‐Isopropyl‐1H‐tetrazole Derivatives

“…The isopropyl groups on the two independent isopropyl‐1 H ‐tetrazoles are oriented above and below the N 4 C (iptz) plane { α = 80.64° [N(1)] and 77.76° [N(5)]}. To the best of our knowledge, only few structures of neutral mononuclear complexes with formula [Fe(L) 4 Cl 2 ], containing azole ligands (1,2,4‐1 H ‐triazole, pyrazole, or substituted pyrazoles) have been reported , …”