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

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 III 2 (dpt −) 2 Cl 4 ] (1) and [Cr III 2 (dpt −) 2 Cl 4 ] (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 III 3 (dpt) 3 Cl 6 ]•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 doublytriazole bridged complex, [V III 2 (N 1-pydpt) 2 Cl 6 ]•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 IV O) 0.84 (V III) 1.16 (N 1-pydpt) 2 Cl 5.16 ]•0.84H 2 O•1.16MeCN (5).

The structural manipulation of a series of Ni4 defective dicubanes: Synthesis, X-ray Structures, Magnetic and Computational analyses

“…16,19,20 Common manipulation methods include changing the bridging groups between the metal ions, or introducing groups either coordinated or free that can form inter/intramolecular interactions, which change the bridging angles, and therefore change the sign and/or magnitude of magnetic interactions. 15,17,18,21 This is well reported in the literature, with examples by Oyarzabal et al, 22 Fig. 1 Schematic representation of the defective dicubane topology, showing the "wingtip" positions in red, the "body" positions in blue, and the bridging atoms in black.…”

“…8,10,[12][13][14] Defective dicubanes have gained popularity due to the coordination chemist's ability to manipulate exchange interactions through synthetic chemistry. [15][16][17][18] For example, tuning of exchange interactions has been shown to be an effective method for quenching quantum tunnelling of magnetization (QTM). 16,19,20 Common manipulation methods include changing the bridging groups between the metal ions, or introducing groups either coordinated or free that can form inter/intramolecular interactions, which change the bridging angles, and therefore change the sign and/or magnitude of magnetic interactions.…”