31191-08-9Relevant articles and documents
Evidence for Reagent-Induced Spin-State Switching in Tripodal Fe(II) Iminopyridine Complexes
Ozumerzifon, Tarik J.,Higgins, Robert F.,Joyce, Justin P.,Kolanowski, Jacek L.,Rappé, Anthony K.,Shores, Matthew P.
, p. 7785 - 7793 (2019)
We present evidence of a spin-state change that accompanies desilylation reactions performed on two related Fe(II) iminopyridine coordination complexes. To probe these systems, we performed titrations with CsF in solution and analyzed the speciation with in situ magnetometry, electrochemistry, and mass spectrometry techniques. We find that pendant tert-butyldimethylsilyl groups are readily cleaved under these conditions, and the resulting desilylated complexes exhibit overall decreased solution magnetic susceptibility values. Density functional theory and ab initio computations probe the impact of substituent identity (prior to- and post-desilylation) on the metal-ligand σ-donor and -acceptor bonding properties. We attribute the observed spin-state changes to the decrease in entropy associated with the conformational freedom of the silylated high-spin complex, resulting in a more favored low-spin state upon desilylation.
Does the solid-liquid crystal phase transition provoke the spin-state change in spin-crossover metallomesogens?
Seredyuk,Gaspar,Ksenofontov,Galyametdinov,Kusz,Guetlich
, p. 1431 - 1439 (2008/09/20)
Three types of interplay/synergy between spin-crossover (SCO) and liquid crystalline (LC) phase transitions can be predicted: (i) systems with coupled phase transitions, where the structural changes associated to the Cr?LC phase transition drives the spin-state transition, (ii) systems where both transifions coexist in the same temperature region but are not coupled, and (iii) systems with uncoupled phase transitions. Here we present a new family of Fe(II) metallomesogens based on the ligand tris[3-aza-4-((5-C n)(6-R)(2-pyridyl))but-3-enyl]amine, with Cn = hexyloxy, dodecyloxy, hexadecyloxy, octadecyloxy, eicosyloxy, R = hydrogen or methyl (Cn-trenH or Cn-trenMe), which affords examples of systems of types i, ii, and iii. Self-assembly of the ligands Cn-trenH and Cn-trenMe with Fe(A)2·xH2O salts have afforded a family of complexes with general formula [Fe(Cn-trenR)](A) 2· sH2O (s > 0), with A = ClO4 -, F-, Cl-, Br- and I-. Single-crystal X-ray diffraction measurements have been performed on two derivatives of this family, named as [Fe(C6-trenH)](ClO 4)2 (C6-1) and [Fe(C6-trenMe)] (ClO4)2 (C6-2), at 150 K for C6-1 and at 90 and 298 K for C6-2. At 150 K, C6-1 displays the triclinic space group P1, whereas at 90 and at 298 K C6-2 adopts the monoclinic P21/c space group. In both compounds the iron atoms adopt a pseudo-octahedral symmetry and are surrounded by six nitrogen atoms belonging to imino groups and pyridines of the ligands Cn-trenH and C n-trenMe. The average Fe(II)-N bonds (1.963(2) A) at 150 K denote that C6-1 is in the low-spin (LS) state. For C6-2 the average Fe(II)-N bonds (2.007(1) A) at 90 K are characteristic of the LS state, while at 298 K they are typical for the high-spin (HS) state (2.234(3) A). Compound C6-1 and [Fe-(C18-trenH)](ClO 4)2 (C18-1) adopts the LS state in the temperature region between 10 and 400 K, while compound C6-2 and [Fe(Cn-trenMe)](ClO4)2 (n = 12 (C 12-2), 18 (C18-2)) exhibit spin crossover behavior at T1/2 centered around 140 K. The thermal spin transition is accompanied by a pronounced change of color from dark red (LS) to orange (HS). The light-induced excited spin state trapping (LIESST) effect has been investigated in compounds C6-2, C12-2 and C 18-2. The T1/2LIESST is 56 K (C6-2), 48 K (C16-2), and 56 K (C18-2). On the basis of differential scanning calorimetry, optical polarizing microscopy, and X-ray diffraction findings for C18-1, C12-2, and C 18-2 at high temperature a smectic mesophase Sx has been identified with layered structures similar to C6-1 and C 6-2. The compounds [Fe(Cn-trenH)](Cl)2· sH2O (n = 16 (C16-3, s = 3.5, C16-4, s = 0.5, C16-5, s = 0), 18 (C18-3, s = 3.5, C18-4, s = 0.5, C18-5, s = 0), 20 (C20-3, s = 3.5, C20-4, s = 0.5, C20-5, s = 0)) and [Fe(C18-tren)](F) 2·sH2O (C18-6, s = 3.5, C 18-7, s= 0) show a very particular spin-state change, while [Fe(C18-tren)](Br)2·3H2O (C 18-8) together with [Fe(C18-tren)](I)2 (C 18-9) are in the LS state (10-400 K) and present mesomorphic behavior like that observed for the complexes C18-1, C12-2, and C18-2. In compounds Cn-3 50% of the Fe(II) ions undergo spin-state change at T1/2 = 375 K induced by releasing water, and in partially dehydrated compounds (s = 0.5) the Cr→SA phase transition occurs at 287 K (C16-4), 301 K (C18-4) and 330 K (C20-4). For the fully dehydrated materials Cn-5 50% of the Fe(II) ions are in the HS state and show paramagnetic behavior between 10 and 400 K. In the partially dehydrated Cn-4 the spin transition is induced by the change of the aggregate state of matter (solid?liquid crystal). For compound C18-6 the full dehydration to C18-7 provokes the spin-state change of nearly 50% of the Fe(II) ions. The compounds Cn-3 and C18-6 are dark purple in the LS state and become light purple-brown when 50% of the Fe(II) atoms are in the HS state.
