Synthesis and Physicochemical Study of Iron(II), Cobalt(II), Nickel(II), and Copper(II) Complexes with 4-(2-Pyridyl)-1,2,4-Triazole

Spin Crossover and High-Spin State in Fe(II) Anionic Polymorphs Based on Tripodal Ligands

“…45 The second system consists on [Fe II 3(μ-L)6(H2O)6] 6− discrete trinuclear anionic units, based on substituted triazole (L 2-) anionic ligand (see scheme 1b), 46 that display a HS-HS-HS to HS-LS-HS transition above room temperature and an unexpected large hysteresis loop (> 85 K) in respect to the parent trinuclear neutral complexes well-known for their gradual SCO behavior without any significant cooperative effects. [47][48][49][50][51][52][53] For the last series, the first Fe(II) SCO anionic complex, described in 2012, consists in the mononuclear [Fe(py4C)(NCS)3] -complex based on the rigid tripodal tetrakis(2pyridyl)methane (py4C) ligand (see schemes 1c, R = py). 54 This complex, of chemical formula [Fe(py4C)2][Fe(py4C)(NCS)3]2, is composed from one LS complex cation, [Fe(py4C)2] 2+ , and from two [Fe((py4C)(NCS)3)] -SCO complexes (see scheme 1d).…”

“…temperature, pressure, or light irradiation). Even though systems based on Co II , − Mn III , − and Fe III − have been increasingly investigated in the past few years thanks to considerable synthetic efforts, those based on the Fe­(II) ion (d 6 electronic configuration) are by far, the most reported systems. − However, while SCO complexes are, for the most part, either cationic or neutral, the few SCO anionic systems reported up today are, to the best of our knowledge, restricted to Fe­(III) − and Fe­(II) ,,− metal ions. Such anionic complexes are however essential for the design of multifunctional materials such as fluorescent or conducting switchable materials, , since they could allow, through appropriate metathesis syntheses, the possibility of introducing functional cations such as fluorescent cations or tetrathiafulvalene (TTF) derivative electron-donor molecules.…”

Synthesis and study of N-(1-phenylethylidene)-N-(4H-1,2,4-triazol-4-yl)amine, N′-(4H-1,2,4-triazol-4-yl)benzamidine, and cobalt(ii), nickel(ii), and copper(ii) complexes based on these ligands

“…9 Hence, we synthesized trinuclear and polynuclear M II complexes with new 1,2,4 triazole derivatives containing a bulky substituent at position 4. It was shown that the introduction of these substituents has no effect on the co ordination mode of 1,2,4 triazoles but influences the com position and magnetic properties of the compounds.…”

“…The terminal ions are also in an octahedral environment due to the involvement of the N atoms of monodentate triazole ligands and (or) the O atoms of wa ter molecules. Depending on the nature of the ligands, the coordination units have the composition MN 3 O 3 (type 1), 5-7 MN 4 O 2 (type 2), 8,9 or MN 5 O (type 3). 5, 10 In addition, triangular trinuclear M II complexes with RTrz were described.…”

Crystal Structure and Magnetic Properties of Trinuclear Transition Metal Complexes (MnII, CoII, NiII and CuII) with Bridging Sulfonate-Functionalized 1,2,4-Triazole Derivatives

“…The chemical design and synthesis of bridging ligands, which provides effective pathways to transmit spin coupling effects, promotes an attractive strategy for creating novel and interesting polynuclear complexes with desirable magnetic properties. In particular, 1,2,4-triazole and its derivatives, due to their capacity to form N 1 -N 2 bridges between metal centers, are interesting ligands for forming stable coordination structures of different dimensionalities, such as discrete polynuclear metal complexes [ 18 , 19 , 20 , 21 ], 1D/2D polymers [ 22 , 23 , 24 , 25 , 26 ] or 3D metal–organic frameworks (MOFs) [ 27 , 28 , 29 , 30 , 31 ]. The N 1 -N 2 -1,2,4-triazole bridges offer short and conjugated diatomic pathways to propagate an effective superexchange between the paramagnetic metal centers.…”