The flexibility of long chain substituents influences spin-crossover in isomorphous lipid bilayer crystals.

[Fe(bpp)2][BF4]2 (bpp = 2,6-di{pyrazol-1-yl}pyridine) derivatives with a bent geometry of hexadec-1-ynyl or hexadecyl pyrazole substituents are isomorphous, and high-spin at room temperature. However, only the latter compound undergoes an abrupt, stepwise spin-transition on cooling. This may reflect the different conformational flexibilities of their long chain substituents.

2,6-Bis(pyrazol-1-yl)pyridine-4-carboxylate Esters with Alkyl Chain Substituents and Their Iron(II) Complexes.

Two series of 4-(alkoxyphenyl) 2,6-bis{pyrazol-1-yl}pyridine-4-carboxyate (LR) or alkyl 2,6-bis{pyrazol-1-yl}pyridine-4-carboxyate (LR) esters have been synthesized and complexed to iron(II), where R = C H ( n = 6, 12, 14, 16, 18); two other derivatives related to LR are also reported. While the solid [Fe(LR)][BF] compounds are isostructural by powder diffraction and show similar spin state behaviors, the [Fe(LR)][BF] series shows more varied structures and magnetic properties. This was confirmed by solvated crystal structures of [Fe(LR)][BF] with n = 6, 14, 16, which all adopt the P1̅ space group but show significantly different side-chain conformations and/or crystal packing.