Fmoc-N-Me-Phe(2-Cl)-OH

The 1:1 assembly reaction of the racemic form of the cross-linking ligand complex Na[CuIILdpen(1R2R/1S2S)] with LnIII(NO3)3·6H2O gave the centrosymmetric circular (CuIILnIII)2 complex [CuIILdpen(1R2R/1S2S)LnIII(NO3)2]2 (1Ln: Ln = Gd, Tb, Dy), while the reaction of the enantiopure form Na[CuIILdpen(1R2R)] with LnIII(NO3)3·6H2O gave the chiral chainlike (CuIILnIII)1∞ complex [CuIILdpen(1R2R)LnIII(NO3)2(CH3CN)]1∞·CH3CN (2Ln: Ln = Gd, Tb, Dy), where {CuIILdpen(1R2R)}- is (N-((1R,2R)-2-(((E)-3-ethoxy-2-oxybenzylidene)amino)-1,2-diphenylethyl)-2-oxybenzamide)copper(II) and {CuIILdpen(1R2R/1S2S)}- is the racemic mixture of {CuIILdpen(1R2R)}- and {CuIILdpen(1S2S)}-. The copper(II) component functions as a cross-linking ligand complex and bridges two LnIII ions at two phenoxo oxygen atoms and one ethoxy oxygen atom, as well as at an amido oxygen atom. For 1Ln, two binuclear species of [CuIILdpen(1R2R)LnIII(NO3)2] and [CuIILdpen(1S2S)LnIII(NO3)2] with opposite chiralities are linked by two amido oxygen atoms O3 and O3* to form a centrosymmetric circular structure with Gd-Cu = 3.370(1) Å and Gd-Cu* = 5.627(1) Å. For 2Ln, binuclear species with the same chirality are bridged by Gd-O3* = 2.228(5) Å to form a chiral chainlike structure with Gd-Cu = 3.3348(9) Å and Gd-Cu* = 6.2326(9) Å. The bridged angles through the amido group of Gd-O3*═C7* are 133.9(5) and 177.6(4)° for 1Gd and 2Gd, respectively. The magnetic susceptibilities of 1Gd and 2Gd were analyzed by the spin-only Hamiltonian on the basis of the circular tetranuclear (-CuIIGdIII-)2 and linear chainlike (-CuIIGdIII-)1∞ structures, respectively. The CuII-GdIII magnetic interactions through two phenoxo bridges and a three-atom N-C═O bridge, J1 and J2, are both ferromagnetic to be J1 = +4.6 cm-1 and J2 = +1.8 cm-1 for 1Gd and J1 = +4.2 cm-1 and J2 = +0.037 cm-1 for 2Gd. The J2 value of 2Gd is much smaller than that of 1Gd. When the temperature was lowered, 1Ln and 2Ln (Ln = Tb, Dy) showed a decrease in the χMT vs T plot due to crystal field effects on the LnIII ion (Stark splitting) and an increase due to the ferromagnetic CuII-LnIII interaction. The magnetization values of 1Ln and 2Ln (Ln = Tb, Dy) without liquid paraffin are considerably larger than the corresponding values with liquid paraffin, indicating the presence of strong magnetic anisotropy. 1Tb and 1Dy showed frequency dependence of ac magnetic susceptibility under zero external dc magnetic field, showing the behavior of single-molecule magnets (SMMs). 2Tb and 2Dy showed no frequency dependence under a zero external magnetic field but showed a meaningful frequency dependence under an external magnetic field. Their energy barriers, Δ/kB, estimated by the Arrhenius plots are 29.4(6) and 20.6(3) K for 1Tb and 2Tb under dc bias fields of 0 and 1000 Oe, respectively, and those of 1Dy and 2Dy are 13.1(9) K and 16.4(2) K under dc bias fields of 0 and 1000 Oe, respectively.

A series of three salen-type lanthanide complexes, e.g., [Dy4(L)2(HL)2Cl2(μ3-OH)2]2Cl2(OH)2·3CH3CH2OH·H2O (1) and [Ln4(L)2(HL)2Cl2(μ3-OH)2]Cl2·5CH3OH·4CH2Cl2 (Ln = Tb(III), 2; Ho(III), 3) have been isolated by the reactions of H2L (H2L = N,N'-bis(3-methoxysalicylidene)cyclohexane-1,2-diamine) with LnCl3·6H2O. X-ray crystallographic analysis reveals that all complexes 1-3 are isostructural, in which four Ln ions and eight O atoms form the distorted defective dicubane {Dy4O8} cores. Magnetic studies indicate that complex 1 exhibits two slow magnetic relaxation processes with effective energy barrier Ueff = 55.71 K under a zero direct-current field, which is attributed to the two coordination geometries of the Dy(III) ions with a salen-type ligand and coordination of a chloride counterion. It represents the highest energy barrier among the salen-type tetranuclear lanthanide single-molecule magnets.

Based on the anion template and chiral ligand inducting role, two series of high-nuclearity 3 d-4 f heterometallic clusters with formulas [NO3@Ln6Cu24(μ3-OH)30(μ2-OH)3(OAc)6( R/ S-L)12(H2O)24](NO3)14· x(H2O) (Ln = Dy, x = 30 for 1a( R-L) and 1b( S-L); Ln = Tb, x = 40 for 2a( R-L) and 2b( S-L)) and (Et3NH)4[Ln6Cu12(μ3-OH)14(μ2-Cl)6Cl12( R/ S-L)12]Cl2· x(H2O) (Ln = Dy, x = 28 for 3a( R-L) and 3b( S-L); Ln = Tb, x = 33 for 4a ( R-L) and 4b( S-L); HL = ( R/ S)-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid), have been synthesized and characterized. Structural analysis reveals that the metal skeleton of compounds 1 and 2 display a Ln6Cu12 octahedral inner core encapsulated by six outer Cu2 units. In the Ln6Cu12 octahedron, 6 Ln3+ ions located at the six vertices and 12 inner Cu2+ ions located at the 12 edges of octahedron, and one NO3- locates in the center of the octahedron. The metal core of compounds 3 and 4 can be viewed as a Ln6 octahedron encapsulated by six Cu2 units. It is interesting that the different inorganic anions involved in the reaction result in the difference in the structures of 1 to 2 and 3 to 4. Circular dichroism spectra of 1-4 display obvious mirror symmetry effect at 600-800 nm of d-d transition of Cu2+, suggesting that the chirality transferred from chiral R- and S-ligand to Cu2+ ions in this system. Notably, the CD peak at the Cu2+ d-d transition position of Ln6Cu12 cluster is obviously blue-shifted compared with that of Ln6Cu24 due to the different coordinated environments of Cu2+. Magnetic studies indicate that 1a and 2a show weak ferromagnetic interactions, while 3a and 4a display antiferromagnetic interactions.