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

Abstract

Seven new dinuclear iron(II) complexes of the general formula [Fe(II)2(PMRT)2](BF4)4·solvent, where PMRT is a 4-substituted-3,5-bis{[(2-pyridylmethyl)-amino]methyl}-4H-1,2,4-triazole, have been prepared in order to investigate the substituent effect on the spin crossover event. Variable temperature magnetic susceptibility and (57)Fe Mössbauer spectroscopy studies show that two of the complexes, [Fe(II)2(PMPT)2](BF4)4·H2O (N(4) substituent is pyrrolyl) and [Fe(II)2(PM(Ph)AT)2](BF4)4 (N(4) is N,N-diphenylamine), are stabilized in the [HS-HS] state between 300 and 2 K with weak antiferromagnetic interactions between the iron(II) centers. Five of the complexes showed gradual half spin crossover, from [HS-HS] to [HS-LS], with the following T(1/2) (K) values: 234 for [Fe(II)2(PMibT)2](BF4)4·3H2O (N(4) is isobutyl), 147 for [Fe(II)2(PMBzT)2](BF4)4 (N(4) is benzyl), 133 for [Fe(II)2(PM(CF3)PhT)2](BF4)4·DMF·H2O (N(4) is 3,5-bis(trifluoromethyl)phenyl), 187 for [Fe(II)2(PMPhT)2](BF4)4 (N(4) is phenyl), and 224 for [Fe(II)2(PMC16T)2](BF4)4 (N(4) is hexadecyl). Structure determinations carried out for three complexes, [Fe(II)2(PMPT)2](BF4)4·4DMF, [Fe(II)2(PMBzT)2](BF4)4·CH3CN, and [Fe(II)2(PM(Ph)AT)2](BF4)4·solvent, revealed that in all three complexes both iron(II) centers are stabilized in the high spin state at 90 K. A general and reliable 4-step route to PMRT ligands is also detailed.

The btp [2,6-bis(1,2,3-triazol-4-yl)pyridine] binding motif: a new versatile terdentate ligand for supramolecular and coordination chemistry

“…[124][125][126][127] In fact, only one research group has investigated the magnetic behaviour of such systems, with others reporting coordination behaviour, effects of the metal ion on emission intensity and electrochemical properties. These systems will now be discussed.…”

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.…”

Structural and magnetic properties of dinuclear Cu(II) complexes featuring triazolyl-naphthalimide ligands

“…Such self-assembled systems have applications in areas including molecular electronics, porous materials for sensing and gas storage, supramolecular spintronics and crystal engineering development. [22,23] Given our interests in the development of magnetically interesting transition metal systems [24][25][26][27][28][29][30][31] and our interests in the development of naphthalimide containing systems [32][33][34] we have combined 1,2,4-triazole coordination chemistry with 1,8-naphthalimide chemistry to generate two new ligands (L 1 and L 2 , scheme 1) that show excellent structure extension through π-based interactions as well as interesting coordination chemistry. These naphthalimide-triazolyl systems are also ideal for the generation of multi-functional architectures as the ligand strands also show excellent fluorescent properties (i.e.…”