Treatment of Fe[BF4]2•6H2O with 4,6-di(pyrazol-1-yl)-1H-pyrimid-2-one (HL 1 ) or 4,6-di(4-methylpyrazol-1-yl)-1Hpyrimid-2-one (HL 2 ) affords solvated crystals of [{Fe III (OH2)6}Fe II 8(-L)12][BF4]7 (1, HL = HL 1 ; 2, HL = HL 2 ). The centrosymmetric complexes contain a cubic arrangement of iron(II) centers, with bis-bidentate [L]ligands bridging the edges of the cube. The encapsulated [Fe(OH2)6] 3+ moiety templates the assembly through twelve O-H…O hydrogen bonds to the [L]hydroxylate groups. All four unique iron(II) ions in the cages are crystallographically high-spin at 250 K, but undergo a gradual high→low spin-crossover on cooling, which is predominantly centered on one iron(II) site and its symmetry-related congener. This was confirmed by magnetic susceptibility data, LIESST effect measurements and, for 1, Mössbauer spectroscopy and diffuse reflectance data. The clusters are stable in MeCN solution, and 1 remains high-spin above 240 K in that solvent. The cubane assembly was not obtained from reactions using other iron(II) salts or 4,6-di(pyrazol-1-yl)pyrimidine ligands, highlighting the importance of hydrogen bonding in templating the cubane assembly.

This report investigates homoleptic iron(II) complexes of thiazolinyl analogues of chiral PyBox tridentate ligands: 2,6-bis(4-phenyl-4,5-dihydrothiazol-2-yl)pyridine (L 1 Ph), 2,6-bis(4-isopropyl-4,5-dihydrothiazol-2-yl)pyridine (L 1 iPr), and 2,6-bis(4tert-butyl-4,5-dihydrothiazol-2-yl)pyridine (L 1 t-Bu). Crystallographic data imply the larger and more flexible thiazolinyl rings reduce steric clashes between the R substituents in homochiral [Fe((R)-L 1 R) 2 ] 2+ or [Fe((S)-L 1 R) 2 ] 2+ (R = Ph, iPr, or t-Bu), compared to their PyBox (L 2 R) analogues. Conversely, the larger heterocyclic S atoms are in close contact with the R substituents in heterochiraland [Fe(L 1 iPr) 2 ] 2+ exhibit spin-crossover equilibria in CD 3 CN, centered at 344 ± 6 K and 277 ± 1 K respectively, while their heterochiral congeners are essentially low-spin within the liquid range of the solvent. These data imply that the diastereomers of [Fe(L 1 Ph) 2 ] 2+ and [Fe(L 1 iPr) 2 ] 2+ show a greater difference in their spin-state behaviors than was previous found for [Fe(L 2 Ph) 2 ] 2+ . Gas-phase DFT calculations (B86PW91/def2-SVP) of the [Fe(L 1 R) 2 ] 2+ and [Fe(L 2 R) 2 ] 2+ complexes reproduce most of the observed trends, but they overstabilize the high-spin state of SCO-active [Fe(L 1 iPr) 2 ] 2+ by ca. 1.5 kcal mol −1 . This might reflect the influence of intramolecular dispersion interactions on the spin states of these compounds. Attempts to model this with the dispersion-corrected functionals B97-D2 or PBE-D3 were less successful than our original protocol, confirming that the spin states of sterically hindered molecules are a challenging computational problem.

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...

[Fe(bpp)2][BF4]2 (bpp = 2,6-di{pyrazol-1-yl}pyridine) derivatives bearing a bent geometry of hexadec-1-ynyl or hexadecyl substituents pyrazole are isomorphous, and high-spin at room temperature. However, only the latter compound undergoes an abrupt,...

Guided-inquiry experiments are an important tool for helping students develop scientific practices such as hypothesizing and problem solving. In organic chemistry, these types of experiments can help students learn how to connect the theory of the reaction to the observation and data to decide how the reaction is proceeding or if it needs adapting. Due to a reduction of in person teaching during the COVID-19 pandemic, we developed a set of virtual inquiry-based organic chemistry experiments where students make the same decisions as they would do with a hands-on inquiry experiment. Thus, these simulations allow students to learn similar problem-solving skills. In this paper, we provide details of the simulations and the educational outcomes when they were used to replace hands-on inquiry experiments. We also include suggestions for its use postpandemic.