Tuning Homochiral Dy2 SMMs Based on ( R )/( S )-2-Chloropropionate through Atom Modification on the Aromatic Rings of Schiff Base Ligands

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Abstract The homochiral ligands (R)- and (S)-2-chloropropionic acid (R-HCPA and S-HCPA) were utilized to construct two pairs of new homochiral Dy2 complexes: [Dy2(R-CPA/S-CPA)2(L1)2(DMF)2]·2DMF (R-I/S-I) {H2L1 = [2-[(E)-(3-hydroxypyridin-2-yl)methylidene]diazanyl](3-aminopyrazin-2-yl)methanone} and [Dy2(R-CPA/S-CPA)2(L2)2(DMF)2] (R-II/S-II) {H2L2 = [2-[(E)-(2-hydroxyphenyl)methylidene]diazanyl](3-aminopyrazin-2-yl)methanone}. Dramatically, the atom modification of N→C(H) on the aromatic ring hydrazone Schiff base ligands caused a significant change in the coordination mode of (R)/(S)-2-chloropropionate (acting as bridging ligands in R-I/S-I and terminal ligands in R-II/S-II), which in turn led to a change in the space group: R-I and S-I are crystallized in the I41 space group but R-II and S-II display the P1 space group. These changes are related to the differences in the way hydrogen bonds form between molecules of these two pairs of enantiomers and whether lattice solvents are present. Magnetic measurements indicate that R-I and R-II are both ferromagnetically coupled and exhibit zero-field single-molecule magnet (SMM) behaviors, which can be explained theoretically. Notably, the magnetic relaxation of R-I consists of the Orbach process plus the weak Raman process, while the magnetic relaxation of R-II belongs to the Raman process plus the QTM, this is related to the fact that R-I is more rigid than R-II due to the rigidity enhanced by the chiral carboxylate-bridging ligands.

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