Di- and Tri-nuclear VIII and CrIII Complexes of Dipyridyltriazoles: Ligand Rearrangements, Mixed Valency and Ferromagnetic Coupling

Julia Rinck; Jonathan A Kitchen; Anthony B Carter; Yanhua Lan; Christopher E Anson; Karin Fink; Sally Brooker; Annie K Powell

doi:10.3389/fchem.2020.00540

Di- and Tri-nuclear V^III and Cr^III Complexes of Dipyridyltriazoles: Ligand Rearrangements, Mixed Valency and Ferromagnetic Coupling

Front Chem. 2020 Jul 9:8:540. doi: 10.3389/fchem.2020.00540. eCollection 2020.

Authors

Julia Rinck^{1

2}, Jonathan A Kitchen^{2

3}, Anthony B Carter¹, Yanhua Lan¹, Christopher E Anson¹, Karin Fink⁴, Sally Brooker², Annie K Powell^{1

4}

Affiliations

¹ Institute of Inorganic Chemistry, Karlsruhe Institute of Technology, Karlsruhe, Germany.
² Department of Chemistry and MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Otago, Dunedin, New Zealand.
³ Chemistry, School of Natural and Computational Sciences, Massey University, Auckland, New Zealand.
⁴ Institute of Nanotechnology, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany.

Abstract

The first dinuclear and trinuclear chromium(III) and dinuclear vanadium(III) complexes of N ⁴-R-substituted-3,5-di(2-pyridyl)-1,2,4-triazole (Rdpt) ligands have been prepared by solvothermal complexations under inert atmospheres, and characterized. The reactions of Cr^III and V^III with adpt (R = amino) resulted in deamination of the ligand and yielded the dinuclear doubly-triazolate bridged complexes [ $V_{2}^{III}$ (dpt ^-)₂Cl₄] (1) and [ ${Cr}_{2}^{III}$ (dpt ^-)₂Cl₄] (2). In the case of the Cr^III complex 2 this bridging results in a rare example of ferromagnetic coupling for a dinuclear Cr^III compound. DFT studies confirm that in 2 the ferromagnetic coupling pathways dominate over the antiferromagnetic pathways, whereas in 1 the reverse occurs, consistent with the observed overall antiferromagnetic coupling in that case. It was also found that the use of different additives in the reaction allows the nuclearity of the Cr^III product to be manipulated, giving either the dinuclear system, or the first example of a trinuclear circular helicate for a Rdpt complex, [ ${Cr}_{3}^{III}$ (dpt)₃Cl₆]·1¾MeCN·¼DCM (3). Reaction of N ⁴ -pydpt (R = 4-pyridyl) with V^III led to an unusual shift of the pyridyl substituent from N ⁴ to N ¹ of the triazole, forming the ligand isomer N ¹ -pydpt, and giving a dinuclear doubly-triazole bridged complex, [ $V_{2}^{III}$ ( N ¹ -pydpt)₂Cl₆]·2MeCN (4). Reaction with Cr^III results in loss of the 4-pyridyl ring and a mixture of the di- and trinuclear complexes, 2 and 3. Interestingly, partial oxidation of the V^III in dinuclear complex 4 to vanadyl V^IV=O was identified by crystallographic analysis of partially oxidized single crystals, [(V^IVO)_0.84(V^III)_1.16( N ¹ -pydpt)₂Cl_5.16]·0.84H₂O·1.16MeCN (5).

Keywords: chromium; deamination; ferromagnetic coupling; helicate; rearrangement; triazole; trinuclear; vanadium.