The number and shape of lattice solvent molecules controls spin-crossover in an isomorphous series of crystalline solvate salts

Abstract

Crystals of [FeL2][BF4]2·nMeCN (L = N-(2,6-di{pyrazol-1-yl}pyrid-4-yl)acetamide; n = 1 or 2) and [FeL2][ClO4]2·MeCN are isomorphous. When n = 1 the compounds exhibit an abrupt, hysteretic spin-transition below 200 K, but...

Spin-Crossover in Iron(II) Complexes of N,N′-Disubstituted 2,6-Bis(Pyrazol-3-yl)Pyridines: An Effect of a Distal Substituent in the 2,6-Dibromophenyl Group

“…H contacts produced by hydrogen atoms of 2,6-dibromophenyl, pyrazolyl or pyridine groups, they result in significant and rather similar contributions (23.7, 20. , as crystal packing effects often prohibit a SCO [23,24] by, for example, inducing an additional distortion to the coordination geometry [23,24]. Indeed, a SCO does not generally [80] occur [81] in iron(II) complexes of 1-bpp [72] with the 'rotation' angle φ < 172° and/or the 'twist' angle θ < 76°, which is the case of [Fe(L R )2](ClO4)2 (Table 3). In the absence of X-ray diffraction data at higher temperatures due to low crystal quality, no conventional (or inverse [82]) SCO in any of the obtained solvates follows from their yellow color common for HS iron(II) complexes [1].…”

“…The latter, however, does not straightforwardly follow from the appropriate angles between the two planes, the centroid-centroid, and shift distances that go from average values of 9.1-9.4°, 3.977-3.986, and 1.174-1.244 Å, respectively, [23,24] by, for example, inducing an additional distortion to the coordination geometry [23,24]. Indeed, a SCO does not generally [80] occur [81] in iron(II) complexes of 1-bpp [72] with the 'rotatioN angle ϕ < 172 • and/or the 'twist' angle θ < 76 • , which is the case of [Fe(L R ) 2 ](ClO 4 ) 2 (Table 3). In the absence of X-ray diffraction data at higher temperatures due to low crystal quality, no conventional (or inverse [82]) SCO in any of the obtained solvates follows from their yellow color common for HS iron(II) complexes [1].…”

“…To decouple the inherent structural features of [Fe(L R ) 2 ](ClO 4 ) 2 from these intermolecular interactions in [Fe(L H ) 2 ](ClO 4 ) 2 •5.5THF, [Fe(L Br ) 2 ](ClO 4 ) 2 •5.5THF•2H 2 O, and [Fe(L Me ) 2 ](ClO 4 ) 2 •2Et 2 O•2CH 3 CN, we performed quantum chemical calculations of the isolated cations [Fe(L R ) 2 ] 2+, as crystal packing effects often prohibit a SCO[23,24] by, for example, inducing an additional distortion to the coordination geometry[23,24]. Indeed, a SCO does not generally[80] occur[81] in iron(II) complexes of 1-bpp[72] with the 'rotatioN angle ϕ < 172 • and/or the 'twist' angle θ < 76 • , which is the case of [Fe(L R ) 2 ](ClO 4 ) 2 (Table3). In the absence of X-ray diffraction data at higher temperatures due to low crystal quality, no conventional (or inverse[82]) SCO in any of the obtained solvates follows from their yellow color common for HS iron(II) complexes[1].In the HS state, the isolated cations [Fe(L R ) 2 ] 2+ feature less distorted and more consistent coordination geometries than those measured experimentally (Tables3 and S2), with weaker intramolecular interactions resulted from an expected overestimation of the Fe-N bond lengths.…”

Structural Insights into Hysteretic Spin‐Crossover in a Set of Iron(II)‐2,6‐bis(1H‐Pyrazol‐1‐yl)Pyridine) Complexes

“…Such geometrical reorganization should be accommodated in the crystal lattice – for example, tight packing of complex entities and high density of crystals blocks such reorganization, [20a] thereby HS‐to‐LS switching is blocked. However, some distorted iron(II)−bpp complexes ( 1 , 2 , 3 , [12b] 5 , [20b] 6 a , [12a] 7 , [21] 8 a , [22] 8 b , [22] and 12 [11] ) featuring ϕ ≤172° undergo spin‐state switching with pronounced Δ T 1/2 . Moreover, complexes 5 , 6 a , 6 b , and 7 all showing remarkable Δ T 1/2 values underwent twisting of bpp ligands (Δ θ ) upon spin‐state switching.…”

Iron(II) Complexes of 4-(Alkyldisulfanyl)-2,6-di(pyrazolyl)pyridine Derivatives. Correlation of Spin-Crossover Cooperativity with Molecular Structure Following Single-Crystal-to-Single-Crystal Desolvation

“… 9 SCO materials that are isomorphous or exhibit variations of the same packing motif are particularly helpful in allowing small differences between materials to be correlated with their switching function within the same lattice environment. 10 − 20 …”