Spin Crossover in Dinuclear N₄S₂ Iron(II) Thioether–Triazole Complexes: Access to [HS-HS], [HS-LS], and [LS-LS] States

Abstract

Access to a new family of thioether-linked PSRT ligands, 4-substituted-3,5-bis{[(2-pyridylmethyl)sulfanyl]methyl}-4H-1,2,4-triazoles (analogues of the previously studied amino-linked PMRT ligands), has been established. Four such ligands have been prepared, PSPhT, PS(i)BuT, PS(t-Bu)PhT, and PS(Me)PhT, with R = Ph, (i)Bu, (t-Bu)Ph, and (Me)Ph, respectively. Three dinuclear colorless to pale green iron(II) complexes, [Fe(II)2(PSRT)2](BF4)4·solvent, featuring N4S2 donor sets, were prepared. Single-crystal structure determinations on [Fe(II)2(PSPhT)2](BF4)4·2MeCN·H2O, [Fe(II)2(PSPhT)2](BF4)4·2(1)/2MeCN·(1)/2H2O·THF, [Fe(II)2(PS(Me)PhT)2](BF4)4·2MeCN, and [Fe(II)2(PS(i)BuT)2](BF4)4·4MeCN reveal that all four are stabilized in the [HS-HS] state to 100 K and that both possible binding modes of the bis-terdentate ligands, cis- and trans-axial, are observed. Variable-temperature magnetic susceptibility studies of air-dried crystals (solvatomorphs of the single crystal samples) reveal the first examples of spin crossover (SCO) for a dinuclear iron(II) complex with N4S2 coordination. Specifically, [Fe(II)2(PSPhT)2](BF4)4·2(1)/2H2O undergoes a multistep but complete SCO from [HS-HS] to [LS-LS], whereas [Fe(II)2(PS(Me)PhT)2](BF4)4·1(1)/2MeCN·2H2O exhibits a half-SCO from [HS-HS] to [HS-LS]. In contrast, [Fe(II)2(PS(i)BuT)2](BF4)4·MeCN·H2O remains [HS-HS] down to 50 K. The reflectance spectrum of pale green [Fe(II)2(PSPhT)2](BF4)4·(1)/2CHCl3·2(1)/2H2O (solvatomorph A) reveals a trace of LS character (572 nm band (1)A1g → (1)T1g). Evans' (1)H NMR method and UV-vis spectroscopy studies revealed that on cooling dark green acetonitrile solutions of these complexes from 313 to 233 K, all three undergo SCO centered at or near room temperature. The tendency of the complexes to go LS in solution reflects the electronic impact of R on the σ-donor strength of the PSRT ligand, whereas the opposite trend in stabilization of the LS state is seen in the solid state, where crystal packing effects, of the R group and solvent content, dominate the SCO behavior.

A Smorgasbord of 17 Cobalt Complexes Active for Photocatalytic Hydrogen Evolution

“…PSPhT, [27] PS Me PhT, [27] PSiBuT, [27] Pydz Et , [28] Pydz Et/Et , [29] and Pym Et/Me [30] were prepared as reported previously.C omplexes [Co II 2 ( tBuPh Trz Me/Me )(m-BF 4 )](BF 4 ) 3 , [23] [Co II 2 ( pyrr Trz Me/Me )(H 2 O) 2 ](BF 4 ) 4 , [23] [Co II 2 (Pydz Et )(m-Cl)Cl 2 ]Cl, [Co II 2 (Pydz Et/Et )(m-OH)](BF 4 ) 3 · 1 = 2 H 2 O, [29] [Co II (M Et )]BF 4 , [26a] [Co II (M Pr )]BF 4 , [26b] [Co( Br M Et )]BF 4 , [31] [ [24a] [Co III (dmgH) 2 (py)Cl], [32] [Ru-(bpy) 3 ](PF 6 ) 2 , [33] and [Ru(bpy) 3 ]Cl 2 [33] were prepared as previously described.…”

Spin state switching of metal complexes by visible light or hard X-rays

“…Multinuclear SCO complexes have been investigated intensively within the last 15 years, exhibiting promising SCO behaviours for possible applications, in particular binuclear complexes. [57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75][76] Compared to spin state switching in mononuclear compounds, multinuclear complexes promise more drastic changes of the macroscopic material properties. For instance, the total amount of unpaired electrons -and therefore the magnetic moment -as well as their coupling could accumulate over all metallic centres, increasing interactions compared to those in mononuclear complexes (e.g.…”

First Cobalt(II) Spin Crossover Compound with N4S2-Donorset

“…For the thiadiazole-based ligand 2,5-bis[(2-pyridylmethyl)amino]methyl-1,3,4-thiadiazole with pyridyl donor sidearms, the complexes are in the [LS-LS] state at low temperatures and show a gradual but incomplete spin crossover only above room temperature [19]. Inspired by the fruitful work of S. Brooker et al [21], we herein report the modification of the previous reported ligand [19] by replacing the amino for thioether linkages. The longer C-S bonds compared to the C-N bonds 2 of 10 give greater flexibility of the ligand, and thus, should enable the population of the [HS-LS] and/or the [HS-HS] state at elevated temperatures.…”