Precise Control of Homochiral Multifunctional Dy2 Single-Molecule Magnets by Changing the Positions of the Two Heterocyclic Nitrogen Atoms in the Schiff Base Ligands

Two pairs of homochiral Dy2 zero-field single-molecule magnets (SMMs) derived from 3-(perfluorobutyryl)-(+)/(−)-camphor (D-Hpfc/L-Hpfc) were assembled by using two hydrazone Schiff bases with the same molecular formula but different heterocyclic rings (pyrazine vs pyrimidine) as bridging ligands. This provides an excellent opportunity to precisely regulate the homochiral multifunctional SMMs by altering the positions of the two heterocyclic nitrogen atoms in the Schiff base ligands. [Dy2(LSchiff1)2(D-pfc)2(MeOH)2] (D-1)/[Dy2(LSchiff1)2(L-pfc)2(MeOH)2] (L-1) [H2LSchiff1 = {2-[(E)-(3,5-difluoro-2-hydroxyphenyl)methylidene]diazanyl}(pyrazin-2-yl)methanone] is crystallized in the P21 space group, while [Dy2(LSchiff2)2(D-pfc)2(MeOH)2] (D-2)/[Dy2(LSchiff2)2(L-pfc)2(MeOH)2] (L-2) [H2LSchiff2 = {2-[(E)-(3,5-difluoro-2-hydroxyphenyl)methylidene]diazanyl}(pyrimidin-4-yl)methanone] is crystallized in the P1 space group; and only the octagon coordination configuration was observed for the Dy3+ ions of D-1/L-1, while both the octagon and the heptagonal pyramid coordination configurations were observed for the Dy3+ ions of D-2/L-2. As a result, D-1/L-1 shows single magnetic relaxation, while D-2/L-2 displays double magnetic relaxation, though intramolecular ferromagnetic interactions exist in both D-1/L-1 and D-2/L-2. The ab initio calculations were carried out to explain their magnetic properties. Moreover, the magneto-optic effects of D-1/L-1 and D-2/L-2 were detected by their magnetic circular dichroism spectra. Furthermore, these two pairs of enantiomers exhibit strong third harmonic generation (THG).