High and Low Spin Mononuclear and Dinuclear Iron(II) Complexes of 4-Amino and 4-Pyrrolyl-3,5-di(2-pyridyl)-4H-1,2,4-triazoles

Abstract

The first dinuclear iron(II) complexes of any 4-substituted 3,5-di(2-pyridyl)-4H-1,2,4-triazole ligands, [Fe(II)2(adpt)2(H2O)1.5(CH3CN)2.5](BF4)4 and [Fe(II)2(pldpt)2(H2O)2(CH3CN)2](BF4)4, are presented [where adpt is 4-amino-3,5-di(2-pyridyl)-4H-1,2,4-triazole and pldpt is 4-pyrrolyl-3,5-di(2-pyridyl)-4H-1,2,4-triazole]. Both dinuclear complexes feature doubly triazole bridged iron(II) centers that are found to be [high spin-high spin] at all temperatures, 4-300 K, and to exhibit weak antiferromagnetic coupling. In the analogous monometallic complexes, [Fe(II)(Rdpt)2(X)2](n+), the spin state of the iron(II) center was controlled by appropriate selection of the axial ligands X. Specifically, both of the chloride complexes, [Fe(II)(adpt)2(Cl)2] x 2 MeOH and [Fe(II)(pldpt)2(Cl)2] x 2 MeOH x H2O, were found to be high spin whereas the pyridine adduct [Fe(II)(adpt)2(py)2](BF4)2 was low spin. Attempts to prepare [Fe(II)(pldpt)2(py)2](BF4)2 and the dinuclear analogues [Fe(II)2(Rdpt)2(py)4](BF4)4 failed, illustrating the significant challenges faced in attempts to develop control over the nature of the product obtained from reactions of iron(II) and these bis-bidentate ligands.

Effect of N4-Substituent Choice on Spin Crossover in Dinuclear Iron(II) Complexes of Bis-Terdentate 1,2,4-Triazole-Based Ligands

“…The Table 2), and are similar to those found for the singly triazole bridged diiron(II) complexes previously reported by this research group. 9 At 4 ·DMF (for which μ eff per Fe is 5.2 μ B at 300 K and 3.8 μ B in the plateau region). 15 Mossbauer Spectroscopy.…”

Synthesis and characterisation of Fe(III) and Co(III) complexes of thiazole-containing thiosemicarbazone ligands

“…Many of the magnetically interesting systems developed to date are significantly labile in solution and undergo ligand displacement giving SCO inactive compounds. [18][19][20][21][22] Therefore developing new ligand systems that can afford favourable coordination environments for SCO and solution stability represents a major challenge in SCO research. Furthermore, ligands that have the ability to be further functionalized (through substituent addition) to allow for targeted immobilization is also desirable, therefore synthetic simplicity and modular synthesis is highly desirable.…”

A highly-thermostable 3D CdII coordination framework based on a new 1,2,4-triazole derivatives: crystal structure, topology and luminescence

“…Up to now, many reports have been published dealing with the coordination properties of the triazoles that have been 3,5-substituted with chelating substituents including 2-pyridyl, 2-pyrazinyl, acetylamino, aminomethyl, hydroxymethyl and carboxyl [2b]. In this regard, the recent research efforts of Prof. Brooker and Prof. Chen are outstanding examples [3][4][5][6][7]. However, in such system of 1,2,4-triazole derivatives, the high-dimension compounds are quite rare, i.e.…”

“…However, in such system of 1,2,4-triazole derivatives, the high-dimension compounds are quite rare, i.e. most of them are bi-and mononuclear compounds [3][4][5][6][7][8][9][10][11], as indicated by a recent Cambridge Structural Database (CSD) search (version 5.32, update 5, Nov 2011). With this aim in mind, we have employed a new 1,2,4-triazole derivatives H 2 L (3-(pyrid-2-yl)-5-(1 H-1,2,4-triazol-3-yl)-1,2,4-triazole) based on the following considerations.…”