Metal acetates form diverse polynuclear complexes with 4-amino-3,5-di(2-pyridyl)-1,2,4-triazole (adpt)

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

The first dinuclear and trinuclear chromium(III) and dinuclear vanadium(III) complexes of N⁴-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 [V2III(dpt⁻)₂Cl₄] (1) and [Cr2III(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, [Cr3III(dpt)₃Cl₆]·1¾MeCN·¼DCM (3). Reaction of N⁴-pydpt (R = 4-pyridyl) with V^III led to an unusual shift of the pyridyl substituent from N⁴ to N¹ of the triazole, forming the ligand isomer N¹-pydpt, and giving a dinuclear doubly-triazole bridged complex, [V2III(N¹-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(N¹-pydpt)₂Cl_5.16]·0.84H₂O·1.16MeCN (5).