Gd Analogue Research Articles

A Dy4 single-molecule magnet and its Gd(iii), Tb(iii), Ho(iii), and Er(iii) analogues encapsulated by an 8-hydroxyquinoline Schiff base derivative and β-diketonate coligand.

Five new tetranuclear complexes based on an 8-hydroxyquinoline Schiff base derivative and the β-diketone coligand, [Ln4(acac)4L6(μ3-OH)2]·CH3CN·0.5CH2Cl2 (Ln = Gd (1), Tb (2), Dy (3), Ho (4) and Er (5); HL = 5-(benzylidene)amino-8-hydroxyquinoline; acac = acetylacetonate) have been synthesized, and structurally and magnetically characterized. Complexes 1-5 have similar tetranuclear structures. Each LnIII ion is eight coordinated and its coordination polyhedra can be described as being in a distorted square-antiprismatic geometry. The magnetic studies reveal that 1 features the magnetocaloric effect (MCE) with the magnetic entropy change of -ΔSm(T) = 25.08 J kg-1 K-1 at 2 K for ΔH = 7 T, and 3 displays the slow magnetic relaxation behavior of Single Molecule Magnets (SMMs) with the anisotropic barrier of 86.20 K and the pre-exponential factor τ0 = 2.99 × 10-8 s.

Unusual undecanuclear heterobimetallic Zn4Ln7 (Ln = Gd, Dy) nano-sized clusters encapsulating two peroxide anions through spontaneous intake of dioxygen.

The synthesis, characterization and properties of two unprecedented undecanuclear heterobimetallic Zn4Ln7 complexes of formula [Zn4Ln7(L)8(O2)2(OH)4(Cl)4(H2O)4]·Cl·4H2O·4CH3CN (Ln = Gd (1), Dy (2)) encapsulating two peroxide anions are presented, representing a very rare example of a 3d-peroxo-Ln system and expanding the realm of metal-peroxo complexes. These eleven metal ions are arranged in a peculiar structural motif, where Zn4 is located at the peripheral shell wrapping Ln7 in the inner core. The Zn ions are penta-coordinate in all cases, linked to the NO2 donor atoms from the L2- ligand and to a hydroxyl group, and the apical position is occupied by a chloride anion. All LnIII ions in these systems are octa-coordinate with LnO8 and LnNO7 coordination spheres. Magnetocaloric effect (MCE) behavior has been found in the Gd analogue due to multiple low lying excited states arising from antiferromagnetic Gd-Gd exchange interactions. The Dy derivative shows frequency dependent out-of-phase signals indicating the presence of slow relaxation of magnetization below 8 K under zero applied direct current (dc) field, but without reaching a maximum, which is due to a faster quantum tunneling relaxation. The effective barrier extracted from the frequency dependent data is Ueff = 11.2 K and a τ0 of 4.18 × 10-6 s.

A Manganese Alternative to Gadolinium for MRI Contrast.

Contrast-enhanced computed tomography (CT) and magnetic resonance imaging (MRI) are routinely used to diagnose soft tissue and vascular abnormalities. However, safety concerns limit the use of iodinated and gadolinium (Gd)-based CT and MRI contrast media in renally compromised patients. With an estimated 14% of the US population suffering from chronic kidney disease (CKD), contrast media compatible with renal impairment is sorely needed. We present the new manganese(II) complex [Mn(PyC3A)(H2O)](-) as a Gd alternative. [Mn(PyC3A)(H2O)](-) is among the most stable Mn(II) complexes at pH 7.4 (log KML = 11.40). In the presence of 25 mol equiv of Zn at pH 6.0, 37 °C, [Mn(PyC3A)(H2O)](-) is 20-fold more resistant to dissociation than [Gd(DTPA)(H2O)](2-). Relaxivity of [Mn(PyC3A)(H2O)](-) in blood plasma is comparable to commercial Gd contrast agents. Biodistribution analysis confirms that [Mn(PyC3A)(H2O)](-) clears via a mixed renal/hepatobiliary pathway with >99% elimination by 24 h. [Mn(PyC3A)(H2O)](-) was modified to form a bifunctional chelator and 4 chelates were conjugated to a fibrin-specific peptide to give Mn-FBP. Mn-FBP binds the soluble fibrin fragment DD(E) with Kd = 110 nM. Per Mn relaxivity of Mn-FBP is 4-fold greater than [Mn(PyC3A)(H2O)](-) and increases 60% in the presence of fibrin, consistent with binding. Mn-FBP provided equivalent thrombus enhancement to the state of the art Gd analogue, EP-2104R, in a rat model of arterial thrombosis. Mn metabolite analysis reveals no evidence of dechelation and the probe was >99% eliminated after 24 h. [Mn(PyC3A)(H2O)](-) is a lead development candidate for an imaging probe that is compatible with renally compromised patients.

Synthesis and anisotropic properties of single crystalline Ln2Ru3Al15+x (Ln=Gd, Tb)

Single crystals of Ln2Ru3Al15+x (Ln=Gd, Tb) have been grown using the self-flux method under Ru-poor conditions. The structure of the Gd analog is found to be highly dependent on the synthesis method. Gd2Ru3Al15.08 orders antiferromagnetically at 17.5K. Tb2Ru3Al15.05 enters an antiferromagnetic state at 16.6K followed by a likely incommensurate-to-commensurate transition at 14.9K for crystals oriented with H//ab. For crystals oriented with H//c, a broad maximum is observed in the temperature dependent M/H, indicative of a highly anisotropic magnetic system with the hard axis in the c-direction. The magnetization as a function of field and magnetoresistance along the ab-direction of Tb2Ru3Al15.05 display a stepwise behavior and indicate strong crystalline electric field effects.

Synthesis, structure, and magnetism of non-planar heptanuclear lanthanide(iii) complexes

The reaction of the hydrazone, 2-methoxy-6-(pyridin-2-yl-hydrazonomethyl) phenol (LH) with lanthanide(iii) nitrate salts in the presence of excess triethylamine afforded the heptanuclear Ln(iii) complexes: [Gd7(L)6(μ3-OH)8(NO3)4(H2O)]·(NO3)3·8CH3CN·H2O (), [Tb7(L)6(μ3-OH)8(NO3)4]·(NO3)3·9CH3CN·2CH3OH·3H2O (), [Dy7(L)6(μ3-OH)8(NO3)4(H2O)]·(NO3)3·7CH3CN·3H2O (), [Ho7(L)6(μ3-OH)8(NO3)4]·(NO3)3·11CH3CN·2CH3OH·2H2O () and [Er7(L)6(μ3-OH)8(NO3)4]·(NO3)3·8CH3CN·2CH3OH (). Single crystal X-ray diffraction studies reveal that these complexes are tri-cationic, possessing three nitrate counter anions. The heptanuclear ensemble is non-planar and consists of six [L](-) and eight μ3-OH ligands. These compounds show an interesting structural motif with two incomplete cubes fused to each other through a common Ln(iii) ion. Compound exhibits a magnetocaloric effect, with (-ΔSm(T) = 27.7 J kg(-1) K(-1) at 3 K and under a field change of 0-7 T), while compound shows slow magnetic relaxation at very low temperatures.

Eutectoid Flux Growth and Physical Properties of Single Crystal Ln117Ni54–ySn112–z (Ln = Gd–Dy)

Ln117Ni53–ySn112–z (Ln = Gd–Dy) have been grown via the eutectoid flux growth method, characterized using single crystal X-ray diffraction, and determined to have a face centered cubic unit cell with lattice parameters of a = 30.070(4), 29.862(5), and 29.823(4) A for the Gd, Dy, and Tb analogues. The compounds contain over 1100 atoms per unit cell with a complex bonding network and multiple magnetic sublattices. In addition, disorder is prevalent throughout the structure. These physical characteristics are ideal when searching for ultralow thermal conductivity materials. Magnetic susceptibility and electrical properties are presented, and all analogues exhibit positive Curie–Weiss constants, suggesting ferromagnetic interactions in each compound, in addition to a spin-glass component to the magnetic behavior.

Investigation of Fe incorporation in LnCr2Al20 (Ln = La, Gd, Yb) with 57Fe Mössbauer and Single Crystal X-ray Diffraction

Crystal growth, structure determination, and magnetic properties of LnCr2Al(20-x)Fe(x) (Ln = La, Gd, Yb) adopting the CeCr2Al20 structure type with space group Fd3m, a ∼ 14.5 Å, are reported. Single crystal X-ray diffraction and Mössbauer spectroscopy are employed to fully characterize the crystal structure of LnCr2Al(20-x)Fe(x) (Ln = La, Gd, Yb). LnCr2Al(20-x)Fe(x) (Ln = La, Gd, Yb) are the first pseudoternaries adopting the CeCr2Al20 structure type with a transition metal occupying the main group site. The Yb analogues are Pauli paramagnets with the Yb ion adopting an electronic configuration close to Yb(2+), while the Gd analogues show paramagnetic behavior with no magnetic order down to 3 K.

(2R,3S)-Butane-1,2,3,4-tetraol-κ3O1,O2,O3](ethanol-κO)tris(nitrato-κ2O,O′)samarium(III)

The title SmIII–erythritol complex, [Sm(NO3)3(C2H6O)(C4H10O4)], is isotypic with its Nd, Eu, Y, Gd, Tb and Ho analogues. The SmIII cation exhibits a coordination number of ten and is chelated by a tridentate erythritol ligand and three bidentate nitrate anions. It is additionally coordinated by an O atom of an ethanol mol­ecule, completing an irregular coordination sphere. The Sm—O bond lengths range from 2.416 (2) to 2.611 (2) Å. In the crystal, extensive O—H⋯O hydrogen bonding involving all hy­droxy groups and some of the nitrate O atoms links the mol­ecules into a three-dimensional network.

Synthesis and Properties of New Multinary Silicides R5Mg5Fe4AlxSi18–x (R = Gd, Dy, Y, x ≈ 12) Grown in Mg/Al Flux

Reactions of iron, silicon, and R = Gd, Dy, or Y in 1:1 Mg/Al mixed flux produce well-formed crystals of R(5)Mg(5)Fe(4)Al(x)Si(18-x) (x ≈ 12). These phases have a new structure type in tetragonal space group P4/mmm (a = 11.655(2) Å, c = 4.0668(8) Å, Z = 1 and R(1) = 0.0155 for the Dy analogue). The structure features two rare earth sites and one iron site; the latter is in monocapped trigonal prismatic coordination surrounded by silicon and aluminum atoms. Siting of Al and Si was investigated using bond length analysis and (27)Al and (29)Si MAS NMR studies. The magnetic properties are determined by the R elements, with the Gd and Dy analogues exhibiting antiferromagnetic ordering at T(N) = 11.9 and 6.9 K respectively; both phases exhibit complex metamagnetic behavior with varying field.

Isoquinoline-Based Lanthanide Complexes: Bright NIR Optical Probes and Efficient MRI Agents

In the objective of developing ligands that simultaneously satisfy the requirements for MRI contrast agents and near-infrared emitting optical probes that are suitable for imaging, three isoquinoline-based polyaminocarboxylate ligands, L1, L2 and L3, have been synthesized and the corresponding Gd(3+), Nd(3+) and Yb(3+) complexes investigated. The specific challenge of the present work was to create NIR emitting agents which (i) have excitation wavelengths compatible with biological applications and (ii) are able to emit a sufficient number of photons to ensure sensitive NIR detection for microscopic imaging. Here we report the first observation of a NIR signal arising from a Ln(3+) complex in aqueous solution in a microscopy setup. The lanthanide complexes have high thermodynamic stability (log K(LnL) =17.7-18.7) and good selectivity for lanthanide ions versus the endogenous cations Zn(2+), Cu(2+), and Ca(2+) thus preventing transmetalation. A variable temperature and pressure (17)O NMR study combined with nuclear magnetic relaxation dispersion measurements yielded the microscopic parameters characterizing water exchange and rotation. Bishydration of the lanthanide cation in the complexes, an important advantage to obtain high relaxivity for the Gd(3+) chelates, has been demonstrated by (17)O chemical shifts for the Gd(3+) complexes and by luminescence lifetime measurements for the Yb(3+) analogues. The water exchange on the three Gd(3+) complexes is considerably faster (k(ex)(298) = (13.9-15.4) × 10(6) s(-1)) than on commercial Gd(3+)-based contrast agents and proceeds via a dissociative mechanism, as evidenced by the large positive activation volumes for GdL1 and GdL2 (+10.3 ± 0.9 and +10.6 ± 0.9 cm(3) mol(-1), respectively). The relaxivity of GdL1 is doubled at 40 MHz and 298 K in fetal bovine serum (r(1) = 16.1 vs 8.5 mM(-1) s(-1) in HEPES buffer), due to hydrophobic interactions between the chelate and serum proteins. The isoquinoline core allows for the optimization of the optical properties of the luminescent lanthanide complexes in comparison to the pyridinic analogues and provides significant shifts of the excitation energies toward lower values which therefore become more adapted for biological applications. L2 and L3 bear two methoxy substituents on the aromatic core in ortho and para positions, respectively, that further modulate their electronic structure. The Nd(3+) and Yb(3+) complexes of the ligand L3, which incorporates the p-dimethoxyisoquinoline moiety, can be excited up to 420 nm. This wavelength is shifted over 100 nm toward lower energy in comparison to the pyridine-based analogue. The luminescence quantum yields of the Nd(3+) (0.013-0.016%) and Yb(3+) chelates (0.028-0.040%) are in the range of the best nonhydrated complexes, despite the presence of two inner sphere water molecules. More importantly, the 980 nm NIR emission band of YbL3 was detected with a good sensitivity in a proof of concept microscopy experiment at a concentration of 10 μM in fetal bovine serum. Our results demonstrate that even bishydrated NIR lanthanide complexes can emit a sufficient number of photons to ensure sensitive detection in practical applications. In particular, these ligands containing an aromatic core with coordinating pyridine nitrogen can be easily modified to tune the optical properties of the NIR luminescent lanthanide complexes while retaining good complex stability and MRI characteristics for the Gd(3+) analogues. They constitute a highly versatile platform for the development of bimodal MR and optical imaging probes based on a simple mixture of Gd(3+) and Yb(3+)/Nd(3+) complexes using an identical chelator. Given the presence of two inner sphere water molecules, important for MRI applications of the corresponding Gd(3+) analogues, this result is particularly exciting and opens wide perspectives not only for NIR imaging based on Ln(3+) ions but also for the design of combined NIR optical and MRI probes.

Rare Earth Metal Boryl Complexes: Synthesis, Structure, and Insertion of a Carbodiimide and Carbon Monoxide

Among the first of their kind: Scandium boryl complex 1 and its Gd analogue were prepared by reaction of a boryl lithium compound with [Ln(CH2SiMe3)2(THF)x][BPh4] (Ln=Sc, Gd). Reaction of 1 with N,N′-diisopropylcarbodiimide gave bis(amidinate) complex 2, which affords 3 by double CO insertion into the ScB bond, nucleophilic addition of an amidinate, and migration of the SiMe3 to the resulting ketene moiety (see scheme). Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Poly[[tris(μ2-4,4′-bipyridineN,N′-dioxide)hexanitratodigadolinium(III)] dichloromethane disolvate

The title one-dimensional coordination network, {[Gd2(NO3)6(C10H8N2O2)3]·2CH2Cl2}n, is isostructural with the previously reported Tb and Tl coordination networks and to its Eu analog. The GdIII cation is coordinated in a distorted tricapped trigonal-prismatic fashion by nine O atoms from three bridging 4,4′-bipyridine N,N′-dioxide ligands and three chelating nitrate anions. None of the atoms lie on a special position, but there is an inversion center located between the rings of one of the ligands. The network topology is ladder-like, and each ladder inter­acts with six neighboring ladders through C—H⋯O hydrogen bonds. The packing motif of the ladders allows for the formation of channels that run parallel to the a axis; these channels are filled with CH2Cl2 solvent mol­ecules that inter­act with the ladders through C—H⋯O hydrogen bonds

Poly[[tris(μ2-4,4′-bipyridineN,N′-dioxide)hexanitratodieuropium(III)] dichloromethane disolvate

The title one-dimensional coordination network, {[Eu2(NO3)6(C10H8N2O2)3]·2CH2Cl2}n, is isostructural with the previously reported Tb and Tl coordination networks and to its Gd analog. The EuIII cation is coordinated in a distorted tricapped trigonal-prismatic fashion by nine O atoms from three bridging 4,4′-bipyridine N,N′-dioxide ligands and three chelating nitrate anions. None of the atoms lie on a special position, but there is an inversion center located between the rings of one of the ligands. The network topology is ladder-like, and each ladder inter­acts with six neighboring ladders through C—H⋯O hydrogen bonds. The packing motif of the ladders allows for the formation of channels that run parallel to the a axis; these channels are filled with CH2Cl2 solvent mol­ecules that inter­act with the ladders through C—H⋯O hydrogen bonds.

Eu 3+ luminescence in La 5Si 2BO 13 with apatite related structure and magnetic studies in Ln5Si 2BO 13 ( Ln=Gd, Dy)

Eu 3+ photoluminescence is studied in La 5Si 2BO 13 with apatite related structure. La 5− x Eu x Si 2BO 13 [ x=0.05, 0.1, 0.3, 0.5, 0.7, 1.0, 2.0] compositions are synthesized. The emission results shows that Eu 3+ ions occupy two different cationic sites viz., La(1) and La(2). The increase in the intensity of 5 D 0– 7 F 0 line with increasing Eu 3+ content shows the preferential occupancy of Eu 3+ in La(2) site due to the existence of short La(2)–O(4) (free oxide ion) bond. The observation of antiferromagnetic interactions in Gd and Dy analogues supports the structural features elucidates from photoluminescence studies.

Stability, Water Exchange, and Anion Binding Studies on Lanthanide(III) Complexes with a Macrocyclic Ligand Based on 1,7-Diaza-12-crown-4: Extremely Fast Water Exchange on the Gd3+ Complex

The picolinate-derivative ligand based on the 1,7-diaza-12-crown-4 platform (bp12c4(2-)) forms stable Ln(3+) complexes with stability constants increasing from the early to the middle lanthanides, then being relatively constant for the rest of the series (logK(LnL) = 16.81(0.06), 18.82(0.01), and 18.08(0.05) for Ln = La, Gd, and Yb, respectively). The complex formation is fast, allowing for direct potentiometric titrations to assess the stability constants. In the presence of Zn(2+), the dissociation of [Gd(bp12c4)](+) proceeds both via proton- and metal-assisted pathways, and in this respect, this system is intermediate between DTPA-type and macrocyclic, DOTA-type chelates, for which the dissociation is predominated by metal- or proton-assisted pathways, respectively. The Cu(2+) exchange shows an unexpected pH dependency, with the observed rate constants decreasing with increasing proton concentration. The rate of water exchange, assessed by (17)O NMR, is extremely high on the [Gd(bp12c4)(H(2)O)(q)](+) complex (k(ex)(298) = (2.20 +/- 0.15) x 10(8) s(-1)), and is in the same order of magnitude as for the Gd(3+) aqua ion (k(ex)(298) = 8.0 x 10(8) s(-1)). In aqueous solution, the [Gd(bp12c4)(H(2)O)(q)](+) complex is present in hydration equilibrium between nine-coordinate, monohydrated, and ten-coordinate, bishydrated species. We attribute the fast exchange to the hydration equilibrium and to the flexible nature of the inner coordination sphere. The large negative value of the activation entropy (DeltaS = -35 +/- 8 J mol(-1) K(-1)) points to an associative character for the water exchange and suggests that water exchange on the nine-coordinate, monohydrated species is predominant in the overall exchange. Relaxometric and luminescence measurements on the Gd(3+) and Eu(3+) analogues, respectively, indicate strong binding of endogenous anions such as citrate, hydrogencarbonate, or phosphate to [Ln(bp12c4)](+) complexes (K(aff) = 280 +/- 20 M(-1), 630 +/- 50 M(-1), and 250 +/- 20 M(-1), respectively). In the ternary complexes, the inner sphere water molecules are fully replaced by the corresponding anion. Anion binding is favored by the positive charge of the [Ln(bp12c4)](+) complexes and the adjacent position of the two inner sphere water molecules. To obtain information about the structure of the ternary complexes, the [Gd(bp12c4)(HCO(3))] and [Gd(bp12c4)(H(2)PO(4))] systems were investigated by means of density functional theory calculations (B3LYP model). They show that anion coordination provokes an important lengthening of the distances between the donor atoms and the lanthanide ion. The coordination of phosphate induces a more important distortion of the metal coordination environment than the coordination of hydrogencarbonate, in accordance with a higher binding constant for HCO(3)(-) and a more important steric demand of phosphate.

Enzyme-Sensitive Magnetic Resonance Imaging Targeting Myeloperoxidase Identifies Active Inflammation in Experimental Rabbit Atherosclerotic Plaques

Inflammation undermines the stability of atherosclerotic plaques, rendering them susceptible to acute rupture, the cataclysmic event that underlies clinical expression of this disease. Myeloperoxidase is a central inflammatory enzyme secreted by activated macrophages and is involved in multiple stages of plaque destabilization and patient outcome. We report here that a unique functional in vivo magnetic resonance agent can visualize myeloperoxidase activity in atherosclerotic plaques in a rabbit model. We performed magnetic resonance imaging of the thoracic aorta of New Zealand White rabbits fed a cholesterol (n=14) or normal (n=4) diet up to 2 hours after injection of the myeloperoxidase sensor bis-5HT-DTPA(Gd) [MPO(Gd)], the conventional agent DTPA(Gd), or an MPO(Gd) analog, bis-tyr-DTPA(Gd), as controls. Delayed MPO(Gd) images (2 hours after injection) showed focal areas of increased contrast (>2-fold) in diseased wall but not in normal wall (P=0.84) compared with both DTPA(Gd) (n=11; P<0.001) and bis-tyr-DTPA(Gd) (n=3; P<0.05). Biochemical assays confirmed that diseased wall possessed 3-fold elevated myeloperoxidase activity compared with normal wall (P<0.01). Areas detected by MPO(Gd) imaging colocalized and correlated with myeloperoxidase-rich areas infiltrated by macrophages on histopathological evaluations (r=0.91, P<0.0001). Although macrophages were the main source of myeloperoxidase, not all macrophages secreted myeloperoxidase, which suggests that distinct subpopulations contribute differently to atherogenesis and supports our functional approach. The present study represents a unique approach in the detection of inflammation in atherosclerotic plaques by examining macrophage function and the activity of an effector enzyme to noninvasively provide both anatomic and functional information in vivo.

Highly Versatile Rare Earth Tantalate Pyrochlore Nanophosphors

Rare earth tantalate materials are of considerable interest in energy and environmentally related applications including photocatalytic H(2) generation or contaminant decomposition, ion conductivity for batteries and fuel cells, and phosphors for light-emitting diodes (LEDs). These Eu-doped rare earth tantalate pyrochlore nanoparticles, K(1-2x)LnTa(2)O(7-x):Eu(3+) (Ln = Lu, Y, Gd; x = (1)/(3) for Gd, x = 0 for Lu and Y), have quantum yields up to 78% when excited with blue light (464 nm), which is remarkable for nanoparticle forms that can suffer efficiency loss by surface effects or poor crystallinity, and are furthermore quite suitable for LED applications. The Gd analogue with its framework distortions has particularly high quantum yields. The blue excitation peak matches the emission of the GaN LED. The combination of the high quantum yield under blue excitation, low thermal quenching, and chemical stability renders these new materials promising red phosphors for blue-excitation white LEDs for solid-state lighting. In addition, the pyrochlore lattice is very accommodating to dopants and vacancies and will incorporate virtually any metal and coordination environment ranging from four-coordinate to eight-coordinate. Thus, there are virtually unlimited possibilities for tailoring and optimizing photoluminescent properties, as demonstrated by these scoping studies.

Magnetic properties and exchange couplings of one-dimensionally arrayed 4f−3d heterometallic [Ln 2Cu 2] n compounds

Heterometallic polymeric coordination compounds [{Ln(hfac) 2(CH 3OH)} 2{Cu(dmg)(Hdmg)} 2] n ([Ln 2Cu 2] n ; Ln = Tb, Ho, and Er; H 2dmg = dimethylglyoxime; Hhfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione) were synthesized, and the X-ray crystallographic analysis shows that their structures are isomorphous to those of the known ferrimagnetic [Gd 2Cu 2] n and [Dy 2Cu 2] n analogs. The exchange couplings in [Tb 2Cu 2] n , [Ho 2Cu 2] n , and [Er 2Cu 2] n were precisely evaluated by high-frequency EPR and pulsed-field magnetization studies, giving J Tb−Cu/ k B = −0.77(2) K, J Ho−Cu/ k B = −0.250(12) K and J Er−Cu/ k B = −0.149(15) K. They were comparable to those of the Gd and Dy analogs. The absolute value of the exchange coupling parameter monotonically decreases in the order of Gd, Tb, Dy, Ho, and Er.

Five related metal–organic frameworks constructed from [Ln2(SO4)2(H2O)n]2+ units and oxalate or acetate ligands

We have synthesized a series of lanthanide-based metal-organic solids and characterized them through structural, magnetic and luminescence analyses. The nine compounds in the series NH(4)[Ln(SO(4))(H(2)O)(C(2)O(4))] [Ln = Ce, Nd, Eu, Gd (x2), Tb, Dy, Er, Yb] belong to four new three-dimensional (3D) structural groups, which we label CKMOF-4a, -4b, -5a, and -5b. The CKMOF-4a (Ce.) and -4b (Gd., Tb., Dy., Er., Yb.) structures feature [Ln(2)(SO(4))(2)(H(2)O)(2)](2+) units and C(2)O(4)(2-) ligands having the same symmetry operations, but their SO(4)(2-) anions feature different connective modes. These units are extended into one-dimensional ribbons fused together by oxalate ligands to form the two 3D open frameworks. The structures of CKMOF-5a (Nd.) and -5b (Eu., Gd.) comprise networks of c-glide-arranged [Ln(2)(SO(4))(2)(H(2)O)(2)](2+) units, in which the oxalate ligands are encapsulated within eight-membered rings. The networks are supported by distinct sites of oxalate ligands to form the two types of 3D open frameworks, the structural topologies of which are distinguished by the versatile connective modes of the SO(4)(2-) anions. The polymeric phases CKMOF-4b and -5b exist in the Gd analogues. For the Dy analogues, varying the size of the cation used as the template led to the selective precipitation of each of these two phases. The layer structure of [Gd(SO(4))(H(2)O)(2)(CH(3)CO(2))] (Gd.), labelled CKMOF-6, assembled from [Gd(2)(SO(4))(2)(H(2)O)(4)](2+) units and acetate ligands; the geometries of the [Gd(2)O(2)] rhombic units may induce ferromagnetic coupling at low temperature. Eu. and Tb. were luminescent, displaying red and green emissions, respectively.

Anisotropic magnetization studies ofR2CoGa8single crystals (R=Gd, Tb, Dy, Ho, Er, Tm, Y, and Lu)

Single crystals of ${R}_{2}{\text{CoGa}}_{8}$ series of compounds were grown by high temperature solution growth (flux) method. These compounds crystallize in a tetragonal crystal structure with the space group $P4/mmm$. It has been found that ${R}_{2}{\text{CoGa}}_{8}$ phase only forms with the heavier rare earths, starting from Gd with a relatively large $c/a$ ratio of $\ensuremath{\approx}2.6$. The resultant anisotropic magnetic properties of the compounds were investigated along the two principal crystallographic directions of the crystal, viz., along the [100] and [001] directions. The compounds ${\text{Y}}_{2}{\text{CoGa}}_{8}$ and ${\text{Lu}}_{2}{\text{CoGa}}_{8}$ show diamagnetic behavior down to 5 K, pointing out the nonmagnetic nature of Co in these compounds and a relatively low density of electronic states at the Fermi level. Compounds with the magnetic rare earths antiferromagnetically order at temperatures lower than 30 K. The N\'eel temperature of ${\text{Tb}}_{2}{\text{CoGa}}_{8}$ exceeds that of the Gd analog. The easy axis of magnetization for ${R}_{2}{\text{CoGa}}_{8}$ ($R=\text{Tb}$, Dy, and Ho) is found to be along the [001] direction and it changes to the [100] direction for ${\text{Er}}_{2}{\text{CoGa}}_{8}$ and ${\text{Tm}}_{2}{\text{CoGa}}_{8}$, whereas the magnetization of ${\text{Gd}}_{2}{\text{CoGa}}_{8}$ was found to be almost isotropic. The magnetization behavior is analyzed on the basis of crystalline electric field model. The estimated crystal field parameters explain the magnetocrystalline anisotropy in this series of compounds.