Field-induced Single-molecule Magnet Behavior Research Articles

Integrating Polyoxometalate into Dy(III)-based Single-molecule Magnets with Pentagonal Bipyramidal Symmetry.

Polyoxometalates (POMs) with various coordination fashions are versatile ligands for constructing single-ion magnets (SIMs), but enforcing POM-SIMs with a specific geometry remains a synthetic challenge. Herein, we synthesized a POM-cocrystallized DyIII-SIM [Dy(OPPh3)4(H2O)3][PW12O40]·4EtOH (1Dy) and a POM-ligated DyIII-SIM [{Dy(OPPh3)3(H2O)3}{PW12O40}]·Ph3PO·H2O (2Dy) with pentagonal bipyramidal local coordination geometry. Magnetic measurements indicate that 1Dy displays field-induced single-molecule magnet (SMM) behavior and the relaxation is dominated by under-barrier processes. 2Dy exhibits spin-lattice relaxation at a broader temperature region with a reversal barrier over 300 K. Magneto-structural analysis reveals that the enhancement of SMM behavior originated from the equatorial replacement of Ph3PO by POM, which strengthens the axial anisotropy in 2Dy. Luminescent experiments indicate that the characteristic DyIII emissions of 1Dy are covered up by the strong π-π* emission of Ph3PO at low-temperature regions. As for 2Dy, partial DyIII emission persists thanks to the antenna effect between DyIII and POM.

Syntheses and properties of seven 3,4-dichlorobenzoate-based zinc-rare earth heterometallic complexes containing a field-induced Zn(II)-Dy(III)-Dy(III)-Zn(II) single-molecule magnet

Under solvothermal conditions of CH3CH2OH and H2O, a series of 3d-4f heterometallic complexes [Ln2Zn2(3,4-DCB)10(2,2′-bpy)2] [Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5), Er (6) and Yb (7), 3,4-DCB = 3,4-dichlorobenzoic acid, 2,2′-bpy = 2,2′-bipyridine] were synthesized by the reactions of Ln(NO3)3·6H2O, Zn(NO3)2·6H2O, 3,4-HDCB, 2,2′-bpy and NaOH. These complexes were characterized by single crystal X-ray diffraction, powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR) spectroscopy and thermogravimetric analysis (TGA) and differential thermo analysis (DTA). Complexes 1–7 show two types of different zero-dimensional (0D) structures although they have the same molecular formula. Complexes 1–5 are isomorphic, and complexes 6 and 7 are isomorphic. In 1–7, linear tetranuclear clusters are formed from 3,4-DCB connecting Ln(III) and Zn(II). They can be expanded into one-dimensional (1D) supramolecular chains or two-dimensional (2D) supramolecular layers by the intermolecular π–π interactions. The photoluminescent properties of 1, 2, 4 and 5 and the magnetic properties of 3–7 were studied in detail. Complex 5 exhibits an obvious field-induced single-molecule magnet behavior with a Ueff value of approximately 24 K.

In situ hydrolysis of a carbophosphazene ligand leads to one-dimensional lanthanide coordination polymers. Synthesis, structure and dynamic magnetic studies.

An in situ hydrolysis of the P-Cl bonds of the carbophosphazene [{NC(NMe2)}2{NPCl2}] (LPCl2) in the presence of hydrated lanthanide(III) nitrates in a dichloromethane and methanol (2 : 1) solvent mixture afforded a series of novel 1D coordination polymers: [{Ln(LHPO2)3(NO3)2(CH3OH)(H2O)} (Cl)]n {where Ln(III) = Gd (1), Tb (2), Dy (3), or Er (4) and LHPO2 is the hydrolyzed carbophosphazene (LPCl2) ligand}. X-ray crystallographic analysis revealed that complexes 1-4 are isostructural and crystallized in the monoclinic crystal system having P21/c space group. The coordination polymers are formed because of the involvement of the geminal P(O)(OH) moieties of the carbophosphazene ligand. Each lanthanide(III) ion is 9-coordinate (9O) in a distorted muffin geometry. Magnetic measurements revealed that both DyIII and ErIII analogues exhibit field-induced single-molecule magnet (SMM) behavior at 0.8 kOe and 2.2 k Oe, respectively. At such dc fields, the dynamic magnetic susceptibility displays complex behavior with a triple magnetic relaxation contribution for 3, while two contributions were identified for 4. The observed static and dynamic magnetic behavior for complexes 1-4 were further rationalized with the aid of BS-DFT and CASSCF/SO-RASSI/SINGLE_ANISO calculations.

Magneto-structural correlation in lanthanide luminescent [2.2]paracyclophane-based single-molecule magnets.

The association of lanthanide ions and paracyclophane derivatives has been very scarcely reported in the literature. In this study, elaboration of five coordination lanthanide complexes involving the 1,4(1,4)-dibenzenacyclohexaphane-12,43-diylbis(diphenylphosphine oxide) ligand (L) was achieved with the determination of single-crystal X-ray diffraction structures of four mononuclear complexes of formula [Ln(hfac)3(L)] (hfac- = 1,1,1,5,5,5-hexafluoroacetylacetonate) (Ln = Dy(III) (1-Dy) and Yb(III) (2-Yb)) and [Ln(tta)3(L)] (tta- = 2-tenoyl-trifluoroacetylacetonate) (Ln = Dy(III) (3-Dy) and Yb(III) (4-Yb)) and one dinuclear complex [Na(Dy2(hfac)6(L)2)](BArF) (BArF- = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) (5-Dy). The compounds were characterized using elemental analysis, IR spectroscopy, DC and AC magnetic measurements and photophysical investigations. L is an efficient organic chromophore for the sensitization of both visible Dy(III) (1-Dy) and near-infrared Yb(III) (2-Yb and 4-Yb) luminescence. The combination of excitation and emission spectra allowed the determination of the crystal field spitting of both the 2F7/2 ground state and 2F5/2 excited state for 2-Yb and 4-Yb. Moreover, 3-Dy and the two Yb(III) derivatives displayed field-induced single-molecule magnet (SMM) behaviour with slow magnetic relaxation occurring through the Raman process only for 2-Yb and 4-Yb, whereas a combination of Orbach and Raman processes was identified for 3-Dy.

A magnetic Ni-based metal-organic framework with interesting transformation dynamics

Herein, a flexible system composed of two Ni(II)-based coordination compounds: a 3D framework of {[Ni(μ-3isoani)2]·DMF}n (1) formula and a 0D monomeric [Ni(3isoani)2(H2O)4] (2) complex (where 3isoani = 3-aminoisonicotinato and DMF = dimethylformamide) which show mutual solvent-induced reversible transformations into each other is reported. The system shows reversible 1 ↔ 2 transformations upon the exposure of one compound to the solvent present in the other, that is, the MOF (1) in water and the monomer (2) in DMF. The process is easily followed by the naked eye because it involves a colour change from green (1)-to-brownish green (2), making the process traceable as previously observed for the Co(II)-based system. Moreover, these compounds present very different magnetic properties since 1 shows field-induced single-molecule magnet (SMM) behaviour, which corresponds to one of the few Ni(II)-based compounds showing single-ion behaviour (being Ni(II) the unique spin carrier), whereas 2 behaves as a regular paramagnet, all of which is explained according to a careful study of the magnetic properties by means of experimental direct-current (dc) and alternating-current (ac) measurements. Obtained experimental results are well supported by active space self-consistent field (CASSCF) calculations that allow understanding the slow relaxation occurring in the Ni(II) ion.

Field-Induced Single-Ion Magnet Behavior in Nickel(II) Complexes with Functionalized 2,2':6'-2″-Terpyridine Derivatives: Preparation and Magneto-Structural Study.

Two mononuclear nickel(II) complexes of the formula [Ni(terpyCOOH)2](ClO4)2∙4H2O (1) and [Ni(terpyepy)2](ClO4)2 MeOH (2) [terpyCOOH = 4'-carboxyl-2,2':6',2″-terpyridine and terpyepy = 4'-[(2-pyridin-4-yl)ethynyl]-2,2':6',2″-terpyridine] have been prepared and their structures determined by single-crystal X-ray diffraction. Complexes 1 and 2 are mononuclear compounds, where the nickel(II) ions are six-coordinate by the six nitrogen atoms from two tridentate terpy moieties. The mean values of the equatorial Ni-N bond distances [2.11(1) and 2.12(1) Å for Ni(1) at 1 and 2, respectively, are somewhat longer than the axial ones [2.008(6) and 2.003(6) Å (1)/2.000(1) and 1.999(1) Å (2)]. The values of the shortest intermolecular nickel-nickel separation are 9.422(1) (1) and 8.901(1) Å (2). Variable-temperature (1.9-200 K) direct current (dc) magnetic susceptibility measurements on polycrystalline samples of 1 and 2 reveal a Curie law behavior in the high-temperature range, which corresponds to magnetically isolated spin triplets, the downturn of the χMT product at lower temperatures being due to zero-field splitting effects (D). Values of D equal to -6.0 (1) and -4.7 cm-1 (2) were obtained through the joint analysis of the magnetic susceptibility data and the field dependence of the magnetization. These results from magnetometry were supported by theoretical calculations. Alternating current (ac) magnetic susceptibility measurements of 1 and 2 in the temperature range 2.0-5.5 K show the occurrence of incipient out-phase signals under applied dc fields, a phenomenon that is characteristic of field-induced Single-Molecule Magnet (SMM) behavior, which herein concerns the 2 mononuclear nickel(II) complexes. This slow relaxation of the magnetization in 1 and 2 has its origin in the axial compression of the octahedral surrounding at their nickel(II) ions that leads to negative values of D. A combination of an Orbach and a direct mechanism accounts for the field-dependent relation phenomena in 1 and 2.

Circularly polarized luminescence in the one-dimensional assembly of binaphtyl-based Yb(iii) single-molecule magnets.

Lanthanide ions have attracted great interest owing to their optical and magnetic properties. Single-molecule magnet (SMM) behavior has been a fascinating science for thirty years. Moreover, chiral lanthanide complexes allow the observation of remarkable circularly polarized luminescence (CPL). However, the combination of both SMM and CPL behaviors in a single molecular system is very rare and deserves attention in the design of multifunctional materials. Four chiral one-dimensional coordination compounds involving 1,1'-Bi-2-naphtol (BINOL)-derived bisphosphate ligands and the Yb(iii) centre were synthesized and characterized by powder and single-crystal X-ray diffraction. All the Yb(iii)-based polymers displayed field-induced SMM behavior with magnetic relaxation occurring by applying Raman processes and near infrared CPL in the solid state.

The Assembly of Grid-type Lanthanide Cluster

A dicompartmental Schiff base ligand was synthesized and used for the assembly of a lanthanide grid-like complex. Dinuclear Dy2 and tetranuclear Dy4 complexes were isolated from the reaction of the ligand with different dysprosium salt. Single crystal X-ray diffractions show that the two DyIII ions in Dy2 are adopted in the N3O coordination pockets of the ligand and further coordinated by water molecules, whereas, for Dy4, the four DyIII ions are clamped by four ligands through their terminal N3O coordination pockets, forming a grid-type assembly. Magnetic studies reveal that complex Dy2 shows field-induced single-molecule magnetic behavior under 1000 Oe dc field, complex Dy4 shows fast relaxation under zero field and field-induced single-molecule magnet (SMM) behavior under 500 Oe. The difference in the magnetic relaxation is related to the various deprotonation of the ligand and distinct topology of the assemblies.

Six nickel-lanthanoid heterometallic complexes based on 2,5-dichlorobenzoate and phen: Syntheses, structures and magnetic properties

Six new zero-dimensional (0D) Ni(II)-Ln(III) heterometallic complexes, [Ln2Ni2(2,5-DCB)10(phen)2] [Ln = Nd (1), Sm (2), Eu (3), Gd (4), Tb (5) and Dy (6), 2,5-HDCB = 2,5‑dichlorobenzoic acid, phen = 1,10-phenanthroline], have been successfully synthesized by the reactions of Ln(NO3)3·6H2O, Ni(NO3)2·6H2O, 2,5‑dichlorobenzoic acid, NaOH and 1,10-phenanthroline under solvothermal conditions. All of these complexes have been characterized by single-crystal X-ray diffraction, elemental analysis, FT-IR spectroscopy, powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA) and differential thermoanalysis (DTA). Complexes 1–6 are isomorphous and have a linear tetranuclear cluster structure formed by the 2,5-DCB anions linking the Ni(II) and Ln(III) ions. The adjacent tetranuclear molecules are further extended into a two-dimensional (2D) supramolecular architecture by the π–π interactions. The magnetic properties of 1, 2 and 4–6 were investigated in detail. Complex 6 displays a field-induced single-molecule magnet (SMM) behavior with a Ueff value of 10 K.

Observation of field-induced single-molecule magnet behavior in an octahedrally coordinated binuclear Co2 compound

A binuclear cobalt compound, namely, [Co2(L)2Cl2(H2O)4]·2Cl·2H2O (1), was synthesized by acylhydrazone Schiff base ligand N3-(4-pyridyl)-4-hydroxybenzoylhydrazone (HL) and CoCl2·6H2O. The crystal structure study suggests that each CoII ion in 1 is surrounded by two nitrogen atoms and one oxygen atom from ligand, one chloride ion and two oxygen atoms from two water molecules, giving rise to six-coordinated geometry, where two N atoms from two ligands as bridges link two CoII ions. The direct-current (dc) magnetic susceptibility measurements reveal the existence of antiferromagnetic coupling interaction in 1. The alternating-current (ac) magnetic susceptibility measurements indicate that 1 exhibits field-induced slow magnetic relaxation behavior with energy barrier (Ueff) of 51.80 K, standing out among Co2-SMMs. This study demonstrates that the large magnetic anisotropy of each CoII ion and the weak antiferromagnetic coupling interaction between two CoII ions can improve Co2-SMMs performance effectively.

Dy3 and Gd3 Complexes with Dy3 Exhibiting Field-Induced Single-Molecule Magnet Behaviour

Two trinuclear complexes of formulae [Dy3(µ3-H2O)(hmp)3(CH3COO)3] (1) and [Gd3(µ3-H2O)(hmp)3(CH3COO)3] (2) were synthesized by employing Dy(CH3COO)3·6H2O and Gd(CH3COO)3·6H2O as lanthanide sources and a Schiff-base H2hmp (H2hmp = 2-(((2-hydroxy-3-methoxybenzyl)imino)methyl)-5-methoxyphenol) as a ligand. Single crystal X-ray diffraction analyses reveal that compounds 1 and 2 are isostructural. The three LnIII ions are bridged by three doubly-deprotonated Schiff-base ligands hmp2−, three acetate ions and one µ3-H2O molecule, forming a regular triangle structure (Ln…Ln…Ln angles of 60°, and Ln…Ln distances of 3.812 Å for 1, and 3.838 Å for 2). Magnetic property studies for 1 and 2 indicate that complex 1 displays field-induced single-molecule magnet (SMM) behavior, and there are weak antiferromagnetic interactions among three GdIII ions in complex 2. The main magnetic axes on DyⅢ ions of 1 are calculated by complete-active-space self-consistent field (CASSCF) calculations.

Field-Induced Single Molecule Magnetic Behavior of Mononuclear Cobalt(II) Schiff Base Complex Derived from 5-Bromo Vanillin

A mononuclear Co(II) complex of a Schiff base ligand derived from 5-Bromo-vanillin and 4-aminoantipyrine, that has a compressed tetragonal bipyramidal geometry and exhibiting field-induced slow magnetic relaxation, has been synthesized and characterized by single crystal X-ray diffraction, elemental analysis and molecular spectroscopy. In the crystal packing, a hydrogen-bonded dimer structural topology has been observed with two distinct metal centers having slightly different bond parameters. The complex has been further investigated for its magnetic nature on a SQUID magnetometer. The DC magnetic data confirm that the complex behaves as a typical S = 3/2 spin system with a sizable axial zero-field splitting parameter D/hc = 38 cm−1. The AC susceptibility data reveal that the relaxation time for the single-mode relaxation process is τ = 0.16(1) ms at T = 2.0 K and BDC = 0.12 T.

Rigid N3O2-Pentadentate Ligand-Assisted Octacoordinate Mononuclear Ln(III) Complexes: Syntheses, Characterization, and Slow Magnetization Relaxation.

A series of air-stable mononuclear octacoordinate Ln(III) complexes, [(L)Ln(TPPO)3]OTf (Ln = Y (1·Y); Gd (1·Gd); Tb (1·Tb); Dy (1·Dy); Ho (1·Ho); and Er (1·Er)) and [(L)Ln(TPPO)(NO3)] (Ln = Y (2·Y) and Dy (2·Dy)), are synthesized employing a rigid N3O2-pentadentate chelating ligand as the basis ligand and meridional ancillary ligands (where H2L = 2,6-diacetylpyridine bis-benzoylhydrazone, TPPO = triphenylphosphine oxide, and OTf– = trifluoromethanesulfonate). All the complexes are synthesized under aerobic conditions and characterized comprehensively by spectroscopic and X-ray crystallographic techniques. Magnetic property investigation on the polycrystalline solid samples of 1·Ln (Ln = Gd, Tb, Dy, Ho, and Er) and 2·Dy are reported. A field-induced single-molecule magnet behavior was observed for the Dy derivatives. 1·Dy exhibits the highest effective energy barrier of magnetization reversal, Ueff/kB = 47 K under Hdc = 1 kOe among the complexes presented herein.

Luminescent and Sublimable Binaphthyl-Based Field-Induced Lanthanide Single-Molecule Magnets

The association of the [Ln(hfac)3(H2O)2] metallic building blocks with the new ligand [1,1’-binaphthalene]-8,8’-diylbis(diphenylphosphine oxide) (L) led to the formation of three mononuclear complexes of formula [Ln(hfac)3(L)] (LnIII = Eu (1), Dy (2) and Yb (3)). The mononuclear character of the compounds is due to the bidentate coordination mode adopted by L to link the metal. L allows the observation of the characteristic visible 5D0  7FJ (J = 0-4) EuIII- and near infrared 2F5/2  2F7/2 YbIII- emissions while 2 is only weakly emissive due to the mismatch between the energy positions of the triplet excited state of the ligand and DyIII emissive state. The magnetic data reveal a field-induced Single-Molecule Magnet (SMM) behavior for 2 and 3 with an efficient suppression of the Quantum Tunneling of the Magnetization (QTM). The slow magnetic relaxation occurs through a Raman process while the Orbach contribution is discarded as confirmed by the correlation with the MJ states energy splitting provided by the luminescence spectrum of 3.

Field-induced single-molecule magnet behaviour in a series of dinuclear cobalt(III,II) complexes

We present the synthesis, structure and magnetic characterization of four dinuclear cobalt(III,II) complexes: [(NCS)CoIII(Ln)(µ–OAc)CoII(NCS)]·G, with n/G = 1/CH3OH (1), 2/CH3CN (2), 3/- (3) and 4/CH3OH (4), being H2Ln, four closely related reduced Schiff base ligands: H2L1 = (1,3-propanediyl)bis(iminomethylene)bis(6-methoxyphenol), H2L2 = (1,3-propanediyl)bis(iminomethylene)bis(6-ethoxyphenol), H2L3= (2,2-dimethyl-1,3-propanediyl)-bis(iminomethylene)bis(6-methoxyphenol) and H2L4= (2,2-dimethyl-1,3-propanediyl)-bis(iminomethylene)bis(6-ethoxyphenol). The single crystal X-ray structures of complexes 1–4 show that both cobalt centres in the four complexes adopt a distorted octahedral geometry with Co(III) and Co(II) centres residing at inner N2O2 and outer O4 pockets of the reduced Schiff base, respectively. Magnetic measurements show that all complexes behave as Co(II) monomers, confirming the presence of diamagnetic low spin Co(III) ions, which have also been supported by the spin-density calculation using Density Functional Theory. Additionally, complexes 1–4 show a field-induced slow relaxation of the magnetization at low temperatures that follow direct and Raman mechanisms.

Modulation of the magnetic and photophysical properties in 3d-4f and 4f-4f' heterobimetallic complexes involving a tetrathiafulvalene-based ligand.

The reaction between the 2-(1-(2,6-di(pyrazol-1-yl)-4-methylpyridyl)-4,5-(4,5-bis(propylthio)-tetrathiafulvalenyl)-1H-benzimidazol-2-yl)-pyridine ligand (L), 1 equivalent of Ln(hfac)3·2H2O/Dy(tta)3·2H2O (hfac- = 1,1,1,5,5,5-hexafluoroacetylacetonate, tta- = 2-thenoyltrifluoroacetonate) and M(hfac)2·2H2O leads to the formation of heteroleptic 3d-4f dinuclear complexes of formula [MLn(hfac)5(L)]n (M(II) = Cd, Zn, Co, Mn, Ni and Ln(III) = Dy, Yb, Nd) and [ZnDy(tta)2(hfac)3(L)]·(CH2Cl2). Their X-ray structures reveal that the two coordination sites are occupied by one Ln(III) ion and one M(II) transition metal respectively. The M(II) ions are coordinated to the benzoimidazolylpyridine (bzip) moiety in a N2O4 coordination sphere, while the Ln(III) ions are coordinated to the 2,6-di(pyrazol-1-yl)-4-pyridine (dpp) moiety in a N3O6 surrounding. When Dy(III) ion is used a field-induced Single-Molecule Magnet (SMM) behavior is detected with a magnetic relaxation time slightly dependent to the nature of the vicinal divalent transition metal. On the other hand, when the Yb(III) is used, intense, moderated or quenched 2F5/2 → 2F7/2 NIR luminescence is observed when the Yb(III) ion is respectively associated with the Zn(II), Mn(II) and Ni(II)/Co(II) ion. The emission intensity can be modulated in function of the metal-to-ligand charge transfer and d-d transition intensities. The replacement of the divalent transition metal by a trivalent lanthanide leads to the formation of heteroleptic 4f-4f' dinuclear complexes of formula [Ln2-xLn'x(hfac)6(L)]·a(CH2Cl2)·b(C6H14) and [Dy1.11Nd0.89(tta)3(hfac)3(L)]. The coordination selectivity is based on the radius. Among the 4f-4f' series, the Dy(III) derivatives displayed such ion in N2O6 eight-coordinated sphere allowing the observation of SMM behavior. The three compounds [Dy1.21Nd0.79(hfac)6(L)]·2(CH2Cl2)·(C6H14), [Yb1.04Nd0.96(hfac)6(L)] and [YbPr(hfac)6(L)] displayed respectively Nd(III), modarated Yb(III) and intense Yb(III) NIR emissions.

Oxalate-bridging NdIII-based arsenotungstate with multifunctional NIR-luminescence and magnetic properties

NIR luminescent oxalate-bridging Nd-based arsenotungstate exhibits field-induced single-molecule magnet behavior, and represents the third example of Nd-based POM SMMs.

Observation of Field-Induced Single-Molecule Magnet Behavior in a Binuclear Co2 Compound with Oh Configuration

Observation of Field-Induced Single-Molecule Magnet Behavior in a Binuclear Co2 Compound with Oh Configuration

Enhancing Steric Hindrance via Ligand Design in Dysprosium Complexes: From Induced Slow Relaxation to Zero-Field Single-Molecule Magnet Properties.

The synthesis and magnetic characterization of three novel Dy compounds, [Dy{PPh2S(NtBu)2}2(μ-Cl2)Li(THF)2] (1), [Dy{PhS(NtBu)2}2(μ-Cl2)Li(THF)2] (2), and [Dy{MeS(NtBu)3}2(μ-Cl2)Li(THF)2] (3), based on the sulfur-nitrogen ligands RS(NtBu)x- (where R = PPh2, x = 2 for (1); R = Ph, x = 2 for (2); and R = Me, x = 3 for (3)) are reported. They represent rare examples of lanthanide-based complexes containing sulfur-nitrogen ligands, whose suitability to enhance the magnetic anisotropy in 3d metals was only recently established. Changes in the ligand field environment drastically affect the magnetic properties, with compounds 1 and 2 displaying field-induced single-molecule magnet (SMM) behavior, while compound 3 shows slow relaxation at zero field. These trends strongly suggest that ligand engineering strategies toward linear dysprosium complexes, similar to those for dysprosocenium complexes, should enhance the SMM performances of SN-based lanthanide compounds.

Manipulating a series of Ln-based helix chains or dinuclear complexes by designing two types of Schiff-based ligands: Structure and magnetic properties

As an important means of regulating ligands, steric hindrance effect is always the first choice to construct structures. It is rare to assemble complexes with different topological and structural types by increasing or decreasing the steric hindrance of ligands and to regulate their properties. Here, we successfully obtained two types of lanthanide structures [Ln(H2L1)(NO3)3]n (1: Dy; 2: Gd, H2L1 ​= ​6,6'-((1E,1′E)-((2,2-dimethylpropane-1,3-diyl)bis(azanylylidene))bis(methanylylidene))bis(2-methoxyphenol)) and [Ln2(H2L2)3(NO3)6]·(CH3CN)x·(CH3OH)y (3: Dy, x ​= ​3, y ​= ​0; 4: Gd, x ​= ​y ​= ​2, H2L2 ​= ​6,6'-((1E,1′E)-((2,2-dimethylpropane-1,3-diyl)bis(azanylylidene))bis(methanylylidene))bis(2-ethoxyphenol)), which are controlled by ligands with the steric hindrance effect. For the all structures, the ligands are distorted when they coordinate with lanthanide ions, which make the ligands form helical structures around Ln(III) ions. For chains 1 and 2, there is a single twisted ligand bridging to form a one-dimensional spiral chain between the Ln(III) ion and the Ln(III) ion. But for complexes 3 and 4, there is a helical dinuclear structure formed by the cross-bridging of a double twisted ligand between the Ln(III) ion and the Ln(III) ion. AC magnetic susceptibilities show that chain 1 is a single-molecule magnet (SMM), which exhibits obviously frequency dependent behavior with the energy barriers of 39.6 (3) K and 44.6 (5) K, but complex 3 shows field-induced single-molecule magnetic behavior. The magnetocaloric effects (MCEs) show that chain 2 has bigger value of S than that of complex 4.