Field-induced Single-molecule Magnet Research Articles

End-to-End Azido-Bridged Lanthanide Chain Complexes (Dy, Er, Gd, and Y) with a Pentadentate Schiff-Base [N3O2] Ligand: Synthesis, Structure, and Magnetism.

The syntheses, structure and magnetic properties are reported for five novel 1D polymeric azido-bridged lanthanide complexes with the general formula {[Ln(DAPMBH)(N3)C2H5OH]C2H5OH}n where H2DAPMBH = 2,6-diacetylpyridine bis(4-methoxybenzoylhydrazone)-a new pentadentate pyridine-base [N3O2] ligand and Ln = Dy (1), Y0.930Dy0.070 (2), Er (3), Y0.923Er0.077 (4), and Gd (5). X-ray diffraction analysis of 1-5 show that the central lanthanide atoms are eight-coordinated with the N5O3 donor set originating from the ligand DAPMBH, one coordinated ethanol molecule and two end-to-end type N3- bridges connecting the metal centers into infinite chain. The [LnN5O3] coordination polyhedron can be regarded as a distorted dodecahedron (D2d). AC magnetic measurements revealed that compounds 1-4 show field-induced single-molecule magnet behavior, with estimated energy barriers Ueff ≈ 47-17 K. The experimental study of magnetic properties was complemented by theoretical analysis based on crystal-field calculations. Direct current magnetic susceptibility studies revealed marginally weak intrachain exchange interaction between Ln3+ ions mediated by the end-to-end azide bridging groups (J ≈ -0.015 cm-1 for 5). Comparative analysis of static and dynamic magnetic properties of magnetically concentrated (1, 3) and diluted (2, 4) Dy and Er compounds showed that, despite fascinating 1D azido-bridged chain structure, compounds 1 and 3 are not single-chain magnets; their magnetic behavior is largely due to single-ion magnetic anisotropy of individual Ln3+ ions.

Field-induced single molecule magnet behavior of a three-dimensional Dy(III)-based complex

A novel three-dimensional Dy(III)-based complex [Dy(H2-DHBDC)0.5(DHBDC)0.5(C2H5OH)(H2O)]n·H2O (H4-DHBDC = 2,5-dihydroxy-1,4-terephthalic acid) (1) was fabricated using a hydrothermal method. Such complex was examined by single-crystal X-ray diffraction analysis and then characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, powder X-ray diffraction as well as magnetic properties. The results of single-crystal structure analysis suggested that complex 1 consisted of three-dimensional framework structure and crystallized in the monoclinic system, space group P21/c. The DyIII ion in 1 adopted eight-coordination mode with a triangular dodecahedron. The results of magnetic property investigations suggested that the coordination polymer exhibited slow magnetic relaxation behaviors under 1500 Oe dc field. Furthermore, the frequency dependence of out-of phase (χ″) ac signals for complex 1 displayed two maxima at low temperature, indicating the presence of two relaxation processes.

Magnetic Behavior of Luminescent Dinuclear Dysprosium and Terbium Complexes Derived from Phenoxyacetic Acid and 2,2′-Bipyridine

Two dinuclear lanthanide complexes [Dy2(L1)6(L2)2]·2EtOH (1) and [Tb2(L1)6(L2)2]·2EtOH (2) (HL1 = phenoxyacetic acid and L2 = 2,2′-bipyridine) were synthesized and the crystal structures were determined. In both complexes, the lanthanide centers are nine-coordinated and have a muffin geometry. Detailed magnetic study reveals the presence of field-induced single molecule magnet (SMM) behavior for complex 1, whereas complex 2 is non-SMM in nature. Further magnetic study with 1′, yttrium doped magnetically diluted sample of 1, disclosed the presence of Orbach and Raman relaxation processes with effective energy barrier, ∆E = 16.26 cm−1 and relaxation time, τo = 2.42 × 10−8 s. Luminescence spectra for complexes 1 and 2 in acetonitrile were studied which show characteristic emission peaks for DyIII and TbIII ions, respectively.

Tracking the Multistep Formation of Ln(III) Complexes with in situ Schiff Base Exchange Reaction and its Highly Selective Sensing of Dichloromethane

Four complexes, namely, [Ln2(L2)2(NO3)4]. 2CH3OH (Ln = Tb (1), Dy (2), Ho (3), Er (4), and L2 = (E)-2-methoxy-6-(((pyridin-2-ylmethyl)imino)methyl)phenol), were obtained by reacting (E)-2-((3-methoxy-2-oxidobenzylidene)amino)ethanesulfonate (L1), Ln(NO3)3·6H2O, and 2-aminomethylpyridine at room temperature under solvothermal conditions in methanol for 12 h. The new Schiff base L2 was generated in situ based on the organic ligand L1 and 2-aminomethylpyridine through Schiff base exchange reaction by using lanthanide salts as inductor. A combination of crystallography and mass spectrometry was performed to track the exchange reaction, and the underlying mechanism accompanied by the complex assembly process was clearly presented. The multistep formation mechanism of the above dinuclear complex was also proposed, i.e., [L1] → Dy[L1]/[L2] → Dy[L2] → Dy[L2]2 → Dy2[L2]2. Luminescence test of 1 showed that it had extremely high selectivity to dichloromethane (CH2Cl2). Therefore, we established a quick, simple, and efficient method of detecting CH2Cl2 that enabled strong-luminescence observation with the naked eye. Tests for small amounts of CH2Cl2 in water further indicated the potential of 1 as a test strip for CH2Cl2 fluorescence detection in water samples. Alternating-current magnetic susceptibility studies indicated the field-induced single-molecule magnet behavior of 2.

Sensitization of visible and NIR emitting lanthanide(III) ions in a series of dinuclear complexes of formula [Ln2(μ-2-FBz)2(2-FBz)4(terpy)2]·2(2-HFBz)·2(H2O)

The reaction between 2-fluorobenzoic acid (H-2-FBz), 2,2′:6′,2″-terpyridine (terpy) and different Ln(NO3)3·6H2O salts (Ln = La, Nd, Sm, Eu, Gd, Tb, Dy, Er and Yb) in an ethanol/water solution mixture leads to the formation of dinuclear complexes of formula [Ln2(μ-2-FBz)2(2-FBz)4(terpy)2]·2(H-2-FBz)·2(H2O) (Ln = La (1), Nd (2), Sm (3), Eu (4), Gd (5), Tb (6), Dy (7), Er (8), and Yb (9)). The solid-state photoluminescence study of the complexes shows the sensitisation of the 4f–4f transitions in the visible range in the case of 4, 6 and 7, in the NIR range for 2, 8 and 9, and both in the visible and NIR ranges for complex 3. Magnetic studies reveal single molecule magnet (SMM) behaviour for compound 7 and field-induced SMM behaviour for compounds 2, 8 and 9.

Different single-molecule magnets behaviors of carboxyl bridged dinuclear Dy(III) complexes induced by charged and neutral ligand

Three dinuclear dysprosium complexes, namely, Dy2(DBM)4L2(CH3CH2OH)2·2CH2Cl2(1), Dy2(DBM)4L2(CH3OH)2·2CH2Cl2(2), Dy2(BAC)4L2(CH3CH2OH)2 (3) and yttrium compound Y2(BAC)4L2(CH3CH2OH)2 (3Y) (L = 2,6-dimethoxybenzoic acid, DBM = dibenzoyl methane, BAC = Benzoylacetone), were structurally and magnetically characterized. The single-crystal structures showed that L serves as an effective bridge to link two Dy(III) centers with μ2-η1:η2-O2 coordination mode. Each Dy(III) ion was chelated by two bidentate β-diketonate co-ligands and a methanol or ethanol molecule, leading to an eight-coordinated geometry. The magnetic measurements revealed that all the complexes behaved as field-induced single-molecule magnets, and the ferromagnetic intramolecular interactions between Dy(III) ions are apparent. Strikingly, the alteration of neutral ligands between 1 and 2 did not result in a significant change of their relaxation energy barriers (Ueff/kB = 25.6 K and 26.1 K respectively), while the dramatically enhancement of energy barrier by nearly triple (91.6 K) increase was observed in 3 when modulating the terminal of β-diketonate anion and the open butterfly-shaped hysteresis loop was also observed at 1.8 K in 10% diluted samples of 3. The electrostatic model for the determination of the magnetic anisotropy in Dy complexes implemented by the Magellan program revealed that the dynamic magnetic relaxation is dominated by the charged β-diketonate ligand much more than the neutral ligand in this case.

Series of Chloranilate-Bridged Dinuclear Lanthanide Complexes: Kramers Systems Showing Field-Induced Slow Magnetic Relaxation

A series of chloralilate-bridged dinuclear lanthanide complexes of formula [{LnIII(Tp)2}2(μ-Cl2An)]·2CH2Cl2, where Cl2An2− and Tp− represent the chloranilate and hydrotris (pyrazolyl)borate ligands, respectively, and Ln = Gd (1), Tb (2), Ho (3), Er (4), and Yb (5) was synthesized. All five complexes were characterized by an elemental analysis, infrared spectroscopy, single crystal X-ray diffraction, and SQUID measurements. The complexes 1–5 in the series were all isostructural. A comparison of the temperature dependence of the dc magnetic susceptibility data of these complexes revealed clear differences depending on the lanthanide center. Ac magnetic susceptibility measurements revealed that none of the five complexes exhibited a slow magnetic relaxation under a zero applied dc field. On the other hand, the Kramers systems (complexes 4 and 5) clearly displayed a slow magnetic relaxation under applied dc fields, suggesting field-induced single-molecule magnets that occur through Orbach and Raman relaxation processes.

Crystal structure, magnetic properties and multiplex photoluminescence of Dy-exclusive coordination polymer based on quinoline-2-carboxylic acid

An example of Dy-exclusive 3D coordination polymer [Dy2(L)4Cl2(H2O)4]n (1), was obtained by reacting quinoline-2-carboxylic acid (HL) with DyCl3·6H2O in methanol at 80 °C. Although there are two types of Dy(III) in one independent unit of 1 taking eight coordination positions, they are respectively in different coordination environments. One of Dy(III) is in an O8 coordination environment formed by four O provided by ligand L and four coordinated H2O molecules. The other Dy(III) is in the N2O4Cl2 coordination environment formed by the N2O4 provided by the ligand L and the chloride ion coordinated as terminal groups. The six ligands in a single unit have four different coordination modes. Magnetic studies have shown that 1 exhibits field-induced single-molecule magnets behavior. Photoluminescence test results of the ligand HL and the polymer showed that 1 showed a characteristic band of the lanthanide metal ion in addition to the luminescence behavior of the ligand HL.

Two new metallacrowns with concurrent 9-MC-3 and offset stacked 8-MC-3 frameworks, and field-induced single-molecule magnet behavior

Two novel complexes [Co5(tBu-sao)6(MeO)2Py5] (1) and [Fe(bpy)3]·[Fe6O2(SO4)2(L)4(MeO)4(MeOH)2] (2) have been synthesized through one-pot reactions using tBu-saoH2. Single-crystal X-ray analysis shows that complex 1 possesses a rare concurrent 9-MC-3 structural type, and 2 contains two isolated and off-set stacked 8-MC-3 units. Magnetic studies revealed antiferromagnetic coupling and field-dependent slow magnetic relaxation in 1, and both antiferromagnetic and ferromagnetic interactions in 2.

Trinuclear and Hexanuclear Lanthanide(III) Complexes of the Chiral 3+3 Macrocycle: X-ray Crystal Structures and Magnetic Properties

A new triphenolic hexaaza chiral macrocyclic amine L forms trinuclear complexes 1-3 with rare earth metal lanthanide(III) ions (Ln = Dy, Eu, and Y) with the general formula [Ln3L(μ3-OH)2(NO3)4(H2O)2]· xCH3OH. The crystal structures of the nitrate derivatives of this type reveal the presence of a {Ln3(μ3-OH)2} core within the macrocycle. For the chloride derivative of dysprosium(III) 4, a duplex of the trinuclear compound is formed to give the hexanuclear [Dy6L2(μ3-OH)3(μ3-O)(μ2-Cl)3Cl4(H2O)2] compound, in which two trinuclear macrocyclic units are linked by bridging chloride anions, supplemented by a hydrogen bond connecting the central oxo and hydroxo bridges as well as by weak interactions at the periphery of the macrocycle. The nuclear magnetic resonance spectra of these complexes reveal a dynamic behavior in solution related to exchange of axial ligands and hindered rotation of phenyl substituents. Magnetic studies of the nitrate (1-3) and chloride (4) dysprosium(III) complexes suggest the presence of weak ferromagnetic interactions between neighboring metal centers. The interaction is strongest for compound 1, and for the related duplex compound 4, it appears to be somewhat weaker. The ac susceptibility measurements for complexes 1 and 4 confirm their field-induced single-molecule magnet behavior with the following characteristics: Ueff = 10.6 cm-1 (15.2 K), τ0 = 2.05 × 10-4 s under 2500 Oe dc fields for 1; Ueff = 7.9 cm-1 (11.4 K), τ0 = 1.68 × 10-4 s under a 3000 Oe dc field for 4.

Magnetic Cationic Copper(II) Chains and a Mononuclear Cobalt(II) Complex Containing [Ln(hfac)4]- Blocks as Counterions.

Four new heterospin compounds with molecular formula {[Cu2(hfac)3(TlTrzNIT)2][Ln(hfac)4]} n·C7H16 (LnIII = Gd (1), Tb (2), or Dy (3)) and [Co(hfac)(TlTrzNIT)2][Dy(hfac)4] (4), where hfac is hexafluoroacetylacetonato and TlTrzNIT is the nitronylnitroxide radical 1-( m-tolyl)-1 H-1,2,3-triazole-4-(4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), were obtained. All structures were determined by single-crystal X-ray diffraction. In compounds 1-3, the TlTrzNIT radical is bridge-coordinated to copper(II) ions, leading to positively charged copper(II)-radical chains containing [Ln(hfac)4]- as counterions. In compound 4, the cobalt(II) ion is coordinated to two TlTrzNIT radicals and one hfac ligand in bidentate mode leading to a mononuclear cationic complex that contains [Dy(hfac)4]- as counterion. Magnetic measurements of all complexes were performed. Magnetic data were fit considering the contributions of the copper(II)-radical chain and a paramagnetic gadolinium(III) ion for 1. The sign and magnitude of the magnetic coupling constants extracted from the fit were confirmed by density functional theory calculations. The obtained spin topology shows an alternated ferro-antiferromagnetic chain. Field-induced single molecule magnet behavior was observed for the Dy derivatives 3 and 4, in agreement with CASSCF calculations performed for the latter system.

The effect of the second coordination sphere on the magnetism of [Ln(NO3)3(H2O)3]·(18-crown-6) (Ln = Dy and Er).

The objective of this work was the exploration of the effect of the second coordination sphere on the magnetic properties of [Ln(NO3)3(H2O)3]·(18C6) (Ln = Dy (1) and Er (2)) compounds comprising co-crystallized 18-crown-6 ethers. Both compounds were identified as field-induced single molecule magnets (SMMs) with estimated magnetization reversal barriers Ueff = 66–71 K for 1 and Ueff = 21–24 K for 2. Theoretical calculations with the B3LYP functional revealed substantial change and redistribution of the electrostatic potential upon accounting for the second coordination sphere represented by two 18C6 molecules, which resulted in the change of the crystal-field around metal atoms. As a result, the multireference CASSCF calculations exposed significant impact of the second coordination sphere on the energy splitting of the respective 6H15/2 (DyIII) and 4I15/2 (ErIII) ground states, the magnetization reversal barrier and the magnetic anisotropy parameters. Moreover, the calculated magnetization reversal barriers, Ucalc. = 57 K for 1 and Ucalc. = 16 K for 2, are in good agreement with the experimental values accentuating the importance of the second coordination sphere on the magnetic properties of SMMs.

A family of lanthanide complexes with a bis-tridentate nitronyl nitroxide radical: syntheses, structures and magnetic properties.

Eleven new lanthanide complexes based on a bis-tridentate nitronyl nitroxide radical NIT-Pm2Py (2-(4,6-di(pyridin-2-yl)pyrimidin-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxy-3-oxide), namely (NIT-Pm2Py)Ln(hfac)3 (Ln = Gd (1Gd), Tb (2Tb), Dy (3Dy), Ho (4Ho), Er (5Er), Yb (6Yb)), [(NIT-Pm2Py)Ln2(hfac)6]·xH2O (Ln = Gd (7Gd), Tb (8Tb), Ho (10Ho), x = 0.5 for 7Gd and 1 for 8Tb and 10Ho) and (NIT-Pm2Py)Ln2(hfac)6 (Ln = Dy (9Dy), Er (11Er)) were prepared and characterized. These complexes can be selectively prepared by controlling the reaction ratio of Ln(hfac)3·2H2O to the radical ligand NIT-Pm2Py. Single crystal X-ray crystallographic analyses confirmed that 1Gd-6Yb are isostructural 2p-4f LnIII-radical complexes, in which the NIT-Pm2Py radical acts as a terminal tridentate ligand chelating to one LnIII ion. On the other hand, 7Gd-11Er are isostructural 4f-2p-4f LnIII-radical-LnIII complexes with the NIT-Pm2Py acting as a bridging ligand between two LnIII ions. 7Gd-11Er represent a rare family of complexes showing the NIT bridged 4f-2p-4f three-spin motif. Alternating-current (ac) magnetic susceptibility investigations revealed that complex 6Yb exhibits field-induced frequency dependence, suggesting a possible field-induced single-molecule magnet behavior. Ab initio calculations were performed on all these complexes. The fitting of the magnetic susceptibilities of these complexes indicates weak antiferromagnetic coupling between the LnIII and NIT radical.

Tetrathiafulvalene-Based Helicene Ligand in the Design of a Dysprosium Field-Induced Single-Molecule Magnet.

The design of a coordination complex that involves a ligand combining both a tetrathiafulvalene core and a helicene fragment was achieved thanks to the reaction between the new 2-{1-[2-methyl[6]helicene]-4,5-[4,5-bis(propylthio)tetrathiafulvalenyl]-1H-benzimidazol-2-yl}pyridine ligand (L) and the Dy(hfac)3·2H2O metalloprecursor. Magnetic investigations showed field-induced single-molecule-magnet (SMM) behavior under an applied magnetic field of 1000 Oe for [Dy(hfac)3(L)]·0.5CH2Cl2, while experimentally oriented single-crystal magnetic measurements allowed for determination of the magnetic anisotropy orientation. The magnetic behavior was rationalized through ab initio CASSCF/SI-SO calculations. This redox-active chiral-field-induced SMM paves the way for the design of switchable-multiproperty SMMs.

Enantiopure Benzamidinate/Cyclooctatetraene Complexes of the Rare-Earth Elements: Synthesis, Structure, and Magnetism

Novel chiral rare-earth half sandwich complexes containing the chiral amidinate ligand, (S,S)-N,N′-bis(1-phenylethyl)benzamidinate ((S)-PEBA) or the tBu analogue (S,S)-N,N′-bis(1-phenylethyl) pivalamidinate ((S)-PETA) and the cyclooctatetraene dianion (C8H8)2– (COT) were synthesized. All complexes were fully characterized and the solid state structures were established by single-crystal crystallography. Magnetic property measurements indicated that the complex [{(S)-PETA}Er(COT)(THF)] is a typical field-induced single-molecule magnet (SMM), of which the magnetic properties are in reasonable agreement with high-level quantum chemical calculations. Due to predominantly electrostatic ligand field effects, the relativistic J = 15/2 ground manifold of Er(III) is split into 8 Kramers doublets spanning a range of ∼500 cm–1, representable by means of higher order spin tensor operators. According to the quantum chemical calculations as well as from analysis of the experimental data, the magnetic relaxation pathway...

Field-induced single molecule magnet behavior of a DyIII-NaI one-dimensional chain extended by acetate ions

A novel DyIII-NaI one-dimensional chain, namely [DyIIINaI(L)(CH3CO2)2]n·2CH3CN (1, H2L = N1,N3‑bis(3‑methoxysalicylidene)diethylenetriamine), was synthesized by treating H2L, di-2-pyridyl ketone (dpk), and NaHCO3 with Dy(CH3CO2)2·6H2O in acetonitrile. Complex 1 was characterized by elemental analyses, IR spectroscopy, single-crystal X-ray diffraction analyses and magnetic properties. Structural analyses revealed that 1 consists of a neutral one-dimensional (1D) chain. In each [DyNa] unit, one DyIII and one NaI ions are bridged by two phenoxido O atoms from one L2− ligand and one carboxyl O atom from one CH3CO2−. Moreover, the [DyNa] units were further connected by two carboxyl O atoms from another CH3CO2−. The magnetic studies revealed that 1 exhibits the field-induced single molecule magnet behavior with an effective energy of 13.21 K. The orientation of the anisotropy axes for the DyIII in 1 was estimated by Magellan program, indicating that the directionality of the anisotropic axes is almost collinear to the Dy1-O8 bond, with an angle of 3.085°.

A 2-D dysprosium glutarate exhibiting slow magnetic relaxation and luminescent properties

A 2-D dysprosium glutarate [Dy2(glu)3(phen)2]n (1, glu = glutarate, phen =1,10-phenanthroline) has been synthesized from the hydrothermal reaction of DyCl3, glutaric acid, and phen ligand. Compound 1 displays a classical 2-D (4,4) grid structure constructed by the linkages of Dy3+ ions and three types of glutarate ligands. Compound 1 shows slow magnetic relaxation and luminescent properties. Although some lanthanide glutarates have been reported, they do not exhibit slow magnetic relaxation properties. Compound 1 offers the only example of a dysprosium coordination polymer with field-induced single-molecule magnets (SMMs) based on aliphatic dicarboxylic acids in the absence of ancillary aromatic carboxylic acids.

Field-Induced Single Molecule Magnets of Phosphine- and Arsine-Oxides.

The coordination chemistry of dysprosium and terbium toward phosphine and arsine oxides was further explored. Thus, the new nitrate [M(NO3)3(Ph3PO)3] (M = Tb, 1; Dy, 2), [Dy(NO3)3(EtOH)(Ph3XO)2] (X = P, 3; As, 4), chloride [DyCl2(Ph3AsO)4]Cl (5), triflate [Dy(OTf)2(MePh2PO)4]OTf (6; OTf = triflate) and hexafluoroacetylacetonate [M(hfa)3(Ph3PO)2] (hfa = hexafluoroacetylacetonate; M = Tb, 7; Dy, 8) complexes were isolated and fully characterized. The crystal structures of 1·CH3CN, 2·CH3CN, 4, 5·2.75EtOH·1.25H2O, 6, 7, and 8 show MO9 cores in 1, 2, and 4, with highly distorted geometry, between spherical capped square antiprism and muffin-like, hexacoordinated environments for the dysprosium ions in 5 and 6, with octahedral geometry, and octa-coordination for the lanthanoid metals in 7 and 8, with geometry closer to square antiprism. Comparison of the magnetic behavior of all the complexes allows analyzing which metal ion (Tb or Dy), phosphine or arsine oxide, or anionic ligand favor more the slow relaxation of the magnetization. Alternating current magnetic measurements show that only 2, 4, and 8 present slow relaxation of the magnetization in the presence of an external magnetic field, 8 being the complex with the highest Ueff (44.85 K) of those described herein.

Slow Relaxation of the Magnetization in Bis-Decorated Chiral Helicene-Based Coordination Complexes of Lanthanides

The complexes [Ln2(hfac)6(L)]·nC6H14 (Ln = Dy (1) n = 0, Yb (2) n = 1) with the L chiral 3,14-di-(2-pyridyl)-4,13-diaza[6]helicene ligand (hfac− = 1,1,1,5,5,5-hexafluoroacetylacetonate) have been synthesized in their racemic form and structurally and magnetically characterized. Both complexes behave as field-induced single molecule magnets in the crystalline phase. These magnetic properties were rationalized by ab initio calculations.

Self-assembly and SMM properties of lanthanide cyanocobaltate chain complexes with terpyridine as blocking ligand

A series of novel isomorphic 1D-polymeric complexes {[Ln(terpy)(H2O)3][Co(CN)6]·5H2O}n (Ln = Tb, Dy, Er, Yb; terpy is 2,2';6',2“-terpyridine) was prepared and characterized. Compounds Dy, Er and Yb were found to exhibit properties of field-induced single-molecule magnets with the anisotropy barriers of 68 K, 8 K and 37 K, respectively. Erbium complex Er seems to represent the first known example of Er-based cyanide-bridged 3d-4f SMM, whereas Yb is the second Yb-based one. The effect of the geometry of the coordination environment as well as of ligands field symmetry on SMM behavior of Dy, Er and Yb compounds is discussed. Among the cyanocobaltate-bridged chain complexes, the Dy, Er, Yb are the first series formed by the entire set of heavy Kramers ions which were studied as SMMs.