Spin‐State Switching in Solution

Anion-dependent spin crossover in solution for an iron(ii) complex of a 1H-pyrazolyl ligand

“…2 However, while ultrafast spectroscopy in solution has elucidated the atomistic mechanism of the spin-transition event, 3 interest in solution-phase SCO has otherwise developed more slowly. 4,5 Individual examples of cooperative SCO switching in micelles, 6 a spin-state dependent MRI response from an iron complex, 7 an SCO complex that binds barbiturate in solution 8 and designs of anion-responsive SCO centre, 9,10 have all been demonstrated. These results imply the UV/vis and paramagnetic NMR changes induced by SCO could be of use for sensor applications, for example.…”

“…These results imply the UV/vis and paramagnetic NMR changes induced by SCO could be of use for sensor applications, for example. 5 The anion-dependent complexes [Fe(H2bip)2L] 2+ (H2bip = 2,2 -bi{1,4,5,6-tetrahydropyrimidine}; L = H2bip, bipy etc) are the best characterised system where SCO is triggered by supramolecular host:guest binding. 9 The low-spin state of these complexes is favoured in the presence of strongly associating halide anions, which interact with the chelating N-H groups at the periphery of the H2bip ligands.…”

“…150 K from start to finish. 4,5 The T½ values in Table 1 and Fig. 2, and the van'T Hoff plots, were calculated assuming that the fully high-spin complex exhibits MT = 3.5±0.1 cm 3 mol −1 K under all the conditions used.…”

A Two‐in‐one Pincer Ligand and its Diiron(II) Complex Showing Spin State Switching in Solution through Reversible Ligand Exchange

“…[4,5] In contrast, spin transitions of molecules in solution are relatively rare, and they are usually characterized by gradual SCO following a Boltzmann distribution and resulting in a spin state equilibrium because of the lack of any cooperativity. [6][7][8] As a consequence, in many cases spin transitions in solution are not complete within the phase limitations of the solvent. In addition to genuine SCO, which does not involve any first sphere ligation changes, spin state sensitivity in solution may arise from changes in the metal ions chemical environment, for example from ligand dissociation or substitution reactions, or from triggering events in the second coordination sphere.…”

“…In addition to genuine SCO, which does not involve any first sphere ligation changes, spin state sensitivity in solution may arise from changes in the metal ions chemical environment, for example from ligand dissociation or substitution reactions, or from triggering events in the second coordination sphere. [6,7] In few cases, spin state variations have been associated with reversible solvent binding or with reversible substitution of solvent ligands by weakly coordinating anions. [9,10] Spin state switching in solution has thus been discussed for solution-based chemosensing or MRI contrast applications.…”