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The following iron(II) complexes of 2,6- bis(oxazolinyl)pyridine (PyBox; LH) derivatives are reported: [Fe( LH)2][ClO4]2 ( 1); [Fe(( R)- LMe)2][ClO4]2 (( R)- 2; LMe=2,6- bis{4-methyloxazolinyl}pyridine); [Fe(( R)- LPh)2][ClO4]2 (( R)- 3) and [Fe(( R)- LPh)(( S)- LPh)][ClO4]2 (( RS)- 3; LPh=2,6- bis{4-phenyloxazolinyl}pyridine); and [Fe(( R)- L iPr)2][ClO4]2 (( R)- 4) and [Fe(( R)- L iPr)(( S)- L iPr)][ClO4]2 (( RS)- 4; L iPr=2,6- bis{4- isopropyloxazolinyl}pyridine). Solid ( R)- 3⋅MeNO2 exhibits an unusual very gradual, but discontinuous thermal spin-crossover with an approximate T [ABSTRACT FROM AUTHOR]

The cover image compares the molecular spin states of two diastereomers of a spin‐crossover iron(II) complex. Solution‐phase magnetic measurements show the low‐spin state of the heterochiral (meso) diastereomer is stabilized relative to its homochiral (rac) congener. This reflects a steric clash between phenyl substituents in the rac isomer, which occupies two diagonal quadrants in the molecule. The resultant twisting of the ligand conformation and metal‐coordination sphere explains the observed reduction in the ligand field. More information can be found in the Full Paper by M. A. Halcrow et al. on page 9067. [ABSTRACT FROM AUTHOR]

The following iron(II) complexes of 2,6-bis(oxazolinyl)pyridine (PyBox; L H ) derivatives are reported: [Fe(L H ) 2 ][ClO 4 ] 2 (1); [Fe((R)-L Me ) 2 ][ClO 4 ] 2 ((R)-2; L Me =2,6-bis{4-methyloxazolinyl}pyridine); [Fe((R)-L Ph ) 2 ][ClO 4 ] 2 ((R)-3) and [Fe((R)-L Ph )((S)-L Ph )][ClO 4 ] 2 ((RS)-3; L Ph =2,6-bis{4-phenyloxazolinyl}pyridine); and [Fe((R)-L iPr ) 2 ][ClO 4 ] 2 ((R)-4) and [Fe((R)-L iPr )((S)-L iPr )][ClO 4 ] 2 ((RS)-4; L iPr =2,6-bis{4-isopropyloxazolinyl}pyridine). Solid (R)-3⋅MeNO 2 exhibits an unusual very gradual, but discontinuous thermal spin-crossover with an approximate T1/2 of 350 K. The discontinuity around 240 K lies well below T1/2 , and is unconnected to a crystallographic phase change occurring at 170 K. Rather, it can be correlated with a gradual ordering of the ligand conformation as the temperature is raised. The other solid compounds either exhibit spin-crossover above room temperature (1 and (RS)-3), or remain high-spin between 5-300 K [(R)-2, (R)-4 and (RS)-4]. Homochiral (R)-3 and (R)-4 exhibit more twisted ligand conformations and coordination geometries than their heterochiral isomers, which can be attributed to steric clashes between ligand substituents [(R)-3]; or, between the isopropyl substituents of one ligand and the backbone of the other ((R)-4). In solution, (RS)-3 retains its structural integrity but (RS)-4 undergoes significant racemization through ligand redistribution by 1 H NMR. (R)-4 and (RS)-4 remain high-spin in solution, whereas the other compounds all undergo spin-crossover equilibria. Importantly, T1/2 for (R)-3 (244 K) is 34 K lower than for (RS)-3 (278 K) in CD 3 CN, which is the first demonstration of chiral discrimination between metal ion spin states in a molecular complex., (© 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)