Central LnIII Research Articles

Synthesis, structure, and magnetic properties of lanthanide(III) complexes incorporating a tris-chelate cobalt(III) complex as a metalloligand

A series of CoIII–LnIII–CoIII trinuclear complexes [Ln{Co(Hmtimn)3}2](NO3)3 were prepared by following a simple one-pot synthesis method, mixing an unsymmetrical bidentate ligand 2-(2-imidazolinyl)-6-methoxypheol (H2mtimn) with Co(NO3)2·6H2O and LnX3· 6H2O (where Ln = La, Ce, Pr, Nd, Gd or Dy and X = NO3 − or Cl−) in methanolic solution in the presence of triethylamine in air. In the reaction mixture, this leads to the in situ formation of a tris-chelate CoIII metalloligand unit, which can coordinate LnIII ions through the interactions of phenolato- and methoxy-O donors. X-ray structural analysis revealed that the CoIII metalloligand functions as a rigid tripodal ligand to coordinate to a LnIII ion by six oxygen donors. The two metalloligands in the complex exhibit homochiral aggregation (ΔΔ or ΛΛ) upon coordination to the LnIII ion. The coordination of the central LnIII ion was found to be a distorted icosahedral geometry. Magnetic susceptibility measurements reveal that both cobalt and central lanthanide ions exist in trivalent states.

Effect of diamagnetic Zn(II) ions on the SMM properties of a series of trinuclear ZnDy2 and tetranuclear Zn2Dy2 (LnIII = Dy, Tb, Gd) complexes: combined experimental and theoretical studies.

To study the effect of diamagnetic ions on magnetic interactions, utilizing a compartmental ligand (Z)-2-(hydroxymethyl)-4-methyl-6-((quinolin-8-ylimino)methyl)phenol (LH2), two different series of ZnII-LnIII complexes, namely the trinuclear series of [DyZn2(L)2(μ2-OAc)2(CH3OH)2]·NO3·MeOH (1), [TbZn2(L)2(μ2-OAc)2(CH3OH)2]·NO3·5MeOH·H2O (2), and [GdZn2(L)2(μ2-OAc)2(CH3OH)2]·NO3·MeOH·CHCl3 (3) and the tetranuclear series of [Dy2Zn2(LH)4(NO3)4(μ2OAc)]·NO3·MeOH·H2O (4), [Tb2Zn2(LH)4(NO3)4(μ2-OAc)]·NO3·MeOH·2H2O (5), and [Gd2Zn2(LH)4(NO3)4(μ2-OAc)]·NO3·MeOH·2H2O (6), were synthesized. Trinuclear ZnII-LnIII complexes 1-3 consist of one LnIII ion sandwiched between two peripheral ZnII ions forming a bent type ZnII-DyIII-ZnII array with an angle of 110.64°. Tetranuclear ZnII-LnIII complexes 4-6 are basically a combination of two dinuclear moieties of [LnZn(LH)2(NO3)2]+ connected by one bidentate bridging acetate ion in μ2-OAc coordination mode. The detailed magnetic analysis reveals that complexes 1 and 4 are single molecule magnets having energy barriers of 34.98 K and 46.71 K with relaxation times (τ0) of 5.05 × 10-4 s and 5.24 × 10-4 s, respectively. Ab initio calculations were employed to analyze the magnetic anisotropy and magnetic exchange interaction between the ZnII and LnIII centers with the aim of gaining better insights into the magnetic dynamics of complexes 1-6.

Structure, fluorescence and energy transfer of 2D multinuclear-LnIII-incorporated organic–inorganic hybrid arsenotungstates

A family of isostructural 2D multinuclear LnIII-incorporated organic–inorganic hybrid arsenotungstates were fleetly synthesized, denoted as K4[{Ln(H2O)7}2 {As4W44O143(OH)8(H2O)6(DL-ala)2}{Ln2(H2O)4(DL-ala)}2]‧54H2O (Ln=Sm (1), Eu (2), Gd (3)), containing a centrosymmetric polyanion [{As4W44O143(OH)8(H2O)6(DL-ala)2}{Ln2(H2O)4(DL-ala)}2]8–. The polyanion is constituted of two {As2W19O62(OH)2(H2O)3}6– building blocks encapsulating a deca-nuclear Ln-W heterometallic cluster [W6O21(OH)4(DL-ala)2{Ln2(H2O)4(DL-ala)}2]6–. Obtained compounds were characterized by means of elemental chemical analysis, thermogravimetric, single crystal X-ray and powder diffraction and FT-IR studies. The optical band-gaps of 1 and 2 are 3.05 eV and 3.09 eV, respectively, according to the UV–Vis diffuse reflectance. In addition, 1 and 2 demonstrate the solid-state fluorescence performance (1: orange, 2: red), of which the POMs chromophore can be considered as an antenna ligand to improve luminescence efficiency of LnIII centers via energy migration.

Heterometallic lanthanide complexes with site-specific binding that enable simultaneous visible and NIR-emission.

Macrocyclic lanthanide complexes have become widely developed due to their distinctive luminescence characteristics and wide range of applications in biological imaging. However, systems with sufficient brightness and metal selectivity can be difficult to produce on a molecular scale. Presented herein is the stepwise introduction of differing lanthanide ions in a bis-DO3A/DTPA scaffold to afford three trinuclear bimetallic [Ln2Ln'] lanthanide complexes with site-specific, controlled binding [(Yb2Tb), (Eu2Tb), (Yb2Eu)]. The complexes display simultaneous emission from all LnIII centers across the visible (TbIII, EuIII) and near infra-red (YbIII) spectrum when excited via phenyl ligand sensitization at a wide range of temperatures and are consequently of interest for exploiting imaging in the near infra-red II biological window. Analysis of lifetime data over a range of excitation regimes reveals intermetallic communication between TbIII and EuIII centers and further develops the understanding of multimetallic lanthanide complexes.

Crystal structure, fluorescence properties and biological activity of three µ2-O bridged Ln2 (Ln = Sm, Eu and Tb) compounds

In this paper, three new binuclear Ln‐based compounds with the formula [Ln2(dbm)2(L)2(C2H5OH)2](Ln = Sm (1), Eu (2) and Tb (3); dbm− = 1,3‐dioxo‐1,3‐ diphenylpropan‐2‐ide) have been synthesized via the solvothermal method by using a polyden‐tate Schiff base ligand (H2L = (E)‐N'‐(3‐ethoxy‐2‐hydroxybenzylidene)‐ 3‐hydroxypicolinohydrazide) reacting with Ln(dbm)3·2H2O. Single-crystal X-ray structures reveal that compounds 1–3 are mainly composed of two LnIII ions, two dbm−, two L2−, two C2H5OH, and the two central LnIII ions are connected by two µ2-O atoms forming a “parallelogram-shaped” Ln2O2 core. The investigations on the solid-state fluorescence properties show that the compounds 1–3 display the characteristic lanthanide luminescence at room temperature. Furthermore, biological activities research reveals that compounds 1–3 have greater antibacterial activity than the ligand H2L, and compounds 1–3 with DNA interaction are mainly intercalation, and supplemented by electrostatic binding or groove binding.

Construction of two Ln(III)2 (Ln = Dy and Er) compounds by a polydentate Schiff-based ligand: Structure and remarkable single-molecule magnet behavior

Two novel dinuclear lanthanide-based compounds, [Ln2(dbm)2(L)2(C2H5OH)2] (Ln = Dy (1) and Er (2)) were successfully self-assembled by using a polydentate Schiff-based ligand. The structures and magnetic behaviors of the obtained products 1 and 2 were investigated in detail. Compound 1 is a dinuclear cluster with space group P21/c, while compound 2 has a space group P-1. Compounds 1 and 2 both have a centrosymmetric dinuclear structure, each central LnIII ion is eight-coordinated and the two central ions are bridged together by two μ2O carbonyl oxygen atoms. Magnetic analysis suggests that compound 1 has ferromagnetic coupling between two adjacent DyIII ions. Remarkable slow-relaxation behaviors of magnetization were observed in 1 under 0 dc filed, giving a value of ΔE/kB = 91.88 K with τ0 = 3.65 × 10−8 s.

Exploiting the Fluxionality of Lanthanide Complexes in the Design of Paramagnetic Fluorine Probes.

Fluorine-19 MRI is increasingly being considered as a tool for biomolecular imaging, but the very poor sensitivity of this technique has limited most applications. Previous studies have long established that increasing the sensitivity of 19F molecular probes requires increasing the number of fluorine nuclei per probe as well as decreasing their longitudinal relaxation time. The latter is easily achieved by positioning the fluorine atoms in close proximity to a paramagnetic metal ion such as a lanthanide(III). Increasing the number of fluorine atoms per molecule, however, is only useful inasmuch as all of the fluorine nuclei are chemically equivalent. Previous attempts to achieve this equivalency have focused on designing highly symmetric and rigid fluorinated macrocyclic ligands. A much simpler approach consists of exploiting highly fluxional lanthanide complexes with open coordination sites that have a high affinity for phosphated and phosphonated species. Computational studies indicate that LnIII-TREN-MAM is highly fluxional, rapidly interconverting between at least six distinct isomers. In neutral water at room temperature, LnIII-TREN-MAM binds two or three equivalents of fluorinated phosphonates. The close proximity of the 19F nuclei to the LnIII center in the ternary complex decreases the relaxation times of the fluorine nuclei up to 40-fold. Advantageously, the fluorophosphonate-bound lanthanide complex is also highly fluxional such that all 19F nuclei are chemically equivalent and display a single 19F signal with a small LIS. Dynamic averaging of fluxional fluorinated supramolecular assemblies thus produces effective 19F MR systems.

Magnetooptical Properties of Lanthanide(III) Metal-Organic Frameworks Based on an Iridium(III) Metalloligand.

Integrating magnetic and optical properties into a metal-organic framework (MOF) remains a great challenge. Herein, we have reasonably constructed two 3D magnetooptical MOFs by incorporating a [IrIII(ppy)2(bpy)]+-based fluorescent metalloligand and magnetic LnIII centers. The alternating arrangements of Δ- or Λ-[IrIII(ppy)2(bpy)]+ endow these MOFs with enhanced optical properties. Moreover, the use of DyIII leads to field-induced slow magnetic relaxation. This work provides an effective strategy for the preparation of magnetooptical bifunctional MOFs.

Zero‐field Slow Magnetic Relaxation Behavior of Dy2 in a Series of Dinuclear {Ln2} (Ln=Dy, Tb, Gd and Er) Complexes: A Combined Experimental and Theoretical Study

AbstractA series of dinuclear lanthanide(III) complexes having general formulae [Ln2L2(thd)4] ⋅ 2CH3CN {Ln=DyIII(1), TbIII(2), GdIII(3), ErIII(4)} were successfully synthesized using Schiff base (E)‐2‐((pyridin‐2‐ylmethylene)amino)phenol (LH) and co‐ligand 2,2,6,6‐Tetramethyl‐3,5‐heptanedione (Hthd). The single crystal XRD data shows that complexes possess a dinuclear planar [Ln2(μ2‐O)2]4+ core where phenolate oxygen atoms act as bridges between the two LnIII ions, and that the coordination sphere of LnIII with eight coordination has distorted trigonal dodecahedron geometry. The magnetic analysis shows complex 1 is a single molecule magnet having a zero‐field effective energy barrier (Ueff) of 54.02 K and relaxation time of τo=4.45×10−6 s. Field‐induced SMM behavior has been observed for 4 with an effective energy barrier of 26.9 K and τ0=2.4×10−9 s. CASSCF+RASSI‐SO calculations on 1, 2 and 4 provide deep insight regarding the electronic structure and single‐ion anisotropy of lanthanide ions. Further, using state‐of‐the‐art ab initio calculations, the nature of magnetic anisotropy and magnetic exchange interaction between the LnIII centers is analyzed to shed light on the magnetic dynamics of all the complexes 1–4.

Hydroxyl-and-carboxyl ligand concatenating multi-lanthanide substituted tellurotungstates and electrochemical detection of noradrenaline

Developing and exploring organic–inorganic hybrid multi-lanthanide (Ln) implanted heteropolyoxometalates (HPOMs) has bloomed into an emerging research field. In this article, two neoteric d-gluconic acids (H6GA) concatenating multi-LnIII implanted heteropolytungstates K14H10[Ln4(H2O)4W6(H2GA)4O12(B-α-TeW9O33)4]·60H2O (Ln = La3+ (1), Pr3+ (2)) were obtained in acidic aqueous system. Attractively, in the polyanion structure of 1 and 2, six WVI and four LnIII centers are connected by four flexible H2GA4− ligands via carboxyl and hydroxyl groups, resulting in the heterometallic [Ln4(H2O)4W6(H2GA)4O12]8+ cluster and then the heterometallic cluster is surrounded by four [B-α-TeW9O33]8– segments. Electrochemical measurements for the 1@CFMCN/GCE sensor (CFMCN = carboxyl-functionalized multiwalled carbon nanotube; GCE = glass carbon electrode) demonstrate that 1@CFMCN/GCE shows benign recognition response to detecting noradrenaline (NDA). This research expands the structural diversity of Ln-implanted HPOMs and presents an electrochemical platform of recognizing NDA in the field of biosensors.

Carboxylate-Decorated Aggregation of Octanuclear Co4Ln4 (Ln = Dy, Ho, Yb) Complexes from Ligand-Controlled Hydrolysis: Synthesis, Structures, and Magnetic Properties

One-pot reactions of an asymmetric carboxy-ether-phenol based Schiff base H2L (2-((2-hydroxy-3-methoxybenzylidene)amino)benzoic acid) with selected Ln(NO3)3·nH2O and [Co2(μ-OH2)(O2CCMe3)4(HO2CCMe3)4] (Co2-Piv) in basic MeOH medium resulted in a family of three octanuclear complexes, [CoII4LnIII4L4(μ1,3-Piv)4(μ1,1,3-Piv)2(η1-Piv)2(μ3-OH)4(MeOH)2]·mMeOH·nH2O (Ln = Dy; m = 3, n = 1 (1), Ho; m = 4, n = 0 (2), Yb; m = 3, n = 1 (3)). The coordination aggregates thus obtained were nicely sustained by four ligand anions and eight externally added carboxylate anions showing three different modes of intermetallic connectivity. The options for incorporating different 4f ions in an investigative synthesis, without altering the resulting intermetallic core structure, were successful for the three representative examples. Single-crystal X-ray diffraction studies revealed that the compounds are isostructural and built from two initially formed partial dicubane-type Co2Ln2L2 units. In each of the tetranuclear parts, the metal ion centers are held together by two L2-, two μ3-HO-, three Piv- bridges, one terminal Piv-, and one terminal MeOH. Four carboxylate ends of four L2- units are responsible for connecting two Co2Ln2 units into octanuclear structures. The unique distortion around the CoII centers is achieved from the facile coordination of bigger 4f ions to the adjacent hard OO sites. The distortion is further maintained by the presence of terminal COO- groups from L2-. The dc magnetic susceptibility data revealed ferromagnetic coupling between the CoII and LnIII centers within the series, whereas the ac magnetic susceptibility measurements identified only 1, having a highly anisotropic DyIII ion, as a single-molecule magnet in the absence of any external magnetic field, with an energy barrier Ueff of 12.5 K.

Dinuclear Lanthanide(III) Complexes from the Use of Methyl 2-Pyridyl Ketoxime: Synthetic, Structural, and Physical Studies.

The first use of methyl 2-pyridyl ketoxime (mepaoH) in homometallic lanthanide(III) [Ln(III)] chemistry is described. The 1:2 reactions of Ln(NO3)3·nH2O (Ln = Nd, Eu, Gd, Tb, Dy; n = 5, 6) and mepaoH in MeCN have provided access to complexes [Ln2(O2CMe)4(NO3)2(mepaoH)2] (Ln = Nd, 1; Ln = Eu, 2; Ln = Gd, 3; Ln = Tb, 4; Ln = Dy, 5); the acetato ligands derive from the LnIII—mediated hydrolysis of MeCN. The 1:1 and 1:2 reactions between Dy(O2CMe)3·4H2O and mepaoH in MeOH/MeCN led to the all-acetato complex [Dy2(O2CMe)6(mepaoH)2] (6). Treatment of 6 with one equivalent of HNO3 gave 5. The structures of 1, 5, and 6 were solved by single-crystal X-ray crystallography. Elemental analyses and IR spectroscopy provide strong evidence that 2–4 display similar structural characteristics with 1 and 5. The structures of 1–5 consist of dinuclear molecules in which the two LnIII centers are bridged by two bidentate bridging (η1:η1:μ2) and two chelating-bridging (η1:η2:μ2) acetate groups. The LnIII atoms are each chelated by a N,N’-bidentate mepaoH ligand and a near-symmetrical bidentate nitrato group. The molecular structure of 6 is similar to that of 5, the main difference being the presence of two chelating acetato groups in the former instead of the two chelating nitrato groups in the latter. The geometry of the 9-coordinate LnIII centers in 1, 5 and 6 can be best described as a muffin-type (MFF-9). The 3D lattices of the isomorphous 1 and 5 are built through H-bonding, π⋯π stacking and C-H⋯π interactions, while the 3D architecture of 6 is stabilized by H bonds. The IR spectra of the complexes are discussed in terms of the coordination modes of the organic and inorganic ligands involved. The Eu(III) complex 2 displays a red, metal-ion centered emission in the solid state; the TbIII atom in solid 4 emits light in the same region with the ligand. Magnetic susceptibility studies in the 2.0–300 K range reveal weak antiferromagnetic intramolecular GdIII…GdIII exchange interactions in 3; the J value is −0.09(1) cm−1 based on the spin Hamiltonian Ĥ = −J(ŜGd1·ŜGd2).

Enhancing the barrier height for magnetization reversal in 4d/4f RuIII2LnIII2 "butterfly" single molecule magnets (Ln = Gd, Dy) via targeted structural alterations.

A series of 4d-4f {RuIII2DyIII2} and {RuIII2GdIII2} 'butterfly' (rhombohedral) complexes have been synthesized and characterized and their magnetic properties investigated. Earlier, we have reported the first 4d/4f SMM - [RuIII2DyIII2(OMe)2(O2CPh)4(mdea)2(NO3)2] (1Dy) with a Ueff value of 10.7 cm-1. As the structural distortion around the DyIII centres and the RuIII⋯DyIII exchange interactions are key to enhancing the anisotropy, in this work we have synthesised three more {Ru2Dy2} butterfly complexes where structural alteration around the DyIII centres and alterations to the bridging groups are performed with an aim to improve the magnetic properties. The new complexes reported here are [Ru2Dy2(OMe)2(O2C(4-Me-Ph)4(mdea)2(MeOH)4], 2Dy, [Ru2Dy2(OMe)2(O2C(2-Cl,4,5-F-Ph)4(mdea)2(NO3)2], 3Dy, and an acac derivative [Ru2Dy2(OMe)2(acac)4(NO3)2(edea)2], 4Dy, where acac- = acetylacetonate, edea2- = N-ethyldiethanolamine dianion. Complex 2Dy describes alteration in the DyIII centers, while complexes 3Dy and 4Dy are aimed to alter the RuIII⋯DyIII exchange pathways. To ascertain the 4d-4f exchange, the Gd-analogues of 1Dy and 4Dy were synthesised [Ru2Gd2(OMe)2(O2CPh)4(mdea)2(NO3)2], 1Gd, [Ru2Gd2(OMe)2(acac)4(NO3)2(edea)2], 4Gd. Both ac and dc susceptibility studies were performed on all these complexes, and out-of-phase signals were observed for 3Dy in zero-field while 2Dy and 4Dy show out-of-phase signals in the presence of an applied field. Complex 3Dy reveals a barrier height Ueff of 45 K. To understand the difference in the magnetic dynamic behavior compared to our earlier reported {RuIII2DyIII2} analogue, detailed theoretical calculations based on ab initio CASSCF/RASSI-SO calculations have been performed. Calculations reveal that the JRu⋯Dy value varies from -1.8 cm-1 (4Dy) to -2.4 cm-1 (3Dy). These values are also affirmed by DFT calculations performed on the corresponding GdIII analogues. The origin of the largest barrier and observation of slow magnetic relaxation in 3Dy is routed back to the stronger single-ion anisotropy and stronger JRu⋯Dy exchange which quenches the QTM effects more efficiently. This study thus paves the way forward to tune local structure around the LnIII center and the exchange pathway to enhance the SMM characteristics in other {3d-4f}/{4d-4f} SMMs.

Family of Isomeric CuII-LnIII (Ln = Gd, Tb, and Dy) Complexes Presenting Field-Induced Slow Relaxation of Magnetization Only for the Members Containing GdIII.

The strategic design and synthesis of two isomeric CuII complexes, [CuLA] and [CuLB], of asymmetrically dicondensed N2O3-donor Schiff-base ligands (where H2LA and H2LB are N-salicylidene-N'-3-methoxysalicylidenepropane-1,2-diamine and N-3-methoxysalicylidene-N'-salicylidenepropane-1,2-diamine, respectively) have been accomplished via a convenient CuII template method. These two complexes have been used as metalloligands for the synthesis of three pairs of Cu-Ln isomeric complexes [CuL(μ-NO3)Ln(NO3)2(H2O)]·CH3CN (for complexes 1A-3A, L = LA, and for complexes 1B-3B, L = LB and Ln = Gd, Tb, and Dy, respectively), all of which have been characterized structurally. In all six isomorphous and isostructural complexes, the decacoordinated LnIII centers and pentacoordinated CuII centers possess sphenocorona and square-pyramidal geometries, respectively. The isomeric pair of Cu-Gd compounds shows field-induced slow relaxation of magnetization, although they present the typical isotropic behavior of GdIII complexes, indicating that slow relaxation is not due to the usual energy barrier originating from the magnetic anisotropy. The isostructural derivatives with the ion-anisotropic lanthanides TbIII and DyIII do not show slow magnetic relaxation with or without a direct-current bias field, demonstrating that the magnetic response of the isotropic system CuII-GdIII occurs through different mechanisms than the rest of the Ln cations.

Syntheses and Crystal Structures of a Series of Manganese-Lanthanide-Sodium 12-Metallacrown-4 Dimers

A series of heterotrimetallic manganese-lanthanide-sodium dimer metallacrowns has been synthesized and characterized by single-crystal X-ray analysis: {LnNa[12-MCMn(III)N(shi)-4]}2(iph)4, where LnIII = La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8), Dy (9), Ho (10), Er (11), Tm (12), Yb (13), Lu (14), and Y (15); MC is metallacrown; shi3− is salicylhydroximate; and iph2− is isophthalate. The manganese(III) ions and shi3− ligands generate the 12-MC-4 framework with one LnIII and Na+ ion bound to each [12-MCMn(III)N(shi)-4] on opposite sides of the central MC cavity. The carboxylate groups of the isophthalate ligands bridge between the central LnIII ion and each ring MnIII ion, and the meta-arrangement of the carboxylate groups joins two LnNa[12-MCMn(III)N(shi)-4] units together to form the dimer through the LnIII ions, which reside on the interior of the molecule. The identity of the central LnIII ion slightly impacts the size the [12-MCMn(III)N(shi)-4] framework. As the crystal radius of the LnIII ion increases from LuIII (1.02 A) to LaIII (1.19 A), the 12-MC-4 framework expands to accommodate the larger LnIII ion as the MC cavity increases in size (0.53 A for LuIII to 0.58 A for LaIII) and the average cross cavity MnIII-MnIII and oxime oxygen-oxime oxygen distances also increase (MnIII-MnIII distances: 6.48 A for LuIII to 6.52 A for LaIII; Ooxime-Ooxime distances: 3.66 A for LuIII to 3.75 A for LaIII). In addition, the larger LnIII ions reside further from the MC cavity as indicated by the LnIII-oxime oxygen mean plane (OoxMP) distance. The LnIII-OoxMP distance steadily decreases from LaIII (1.7527(12) A) to LuIII (1.5575(15) A). The complex {LaNa[12-MCMn(III)N(shi)-4]}2(iph)4(DMF)6(H2O)2 is a dimer of [12-MC-4] molecules linked by four isophthalate anions

A series of mononuclear Ln-radical complexes based on 1-methylpyrazole nitronyl nitroxide: Synthesis, structure and magnetic properties

The reaction of LnIII salts (GdIII, TbIII and DyIII) and the 1-methyl-3-pyrazole nitronyl nitroxide radical gives three isostructural complexes, namely [Ln(hfac)3(1-Me-3-NIT-Pyz)] (Ln = Gd (1), Tb (2) and Dy (3); 1-Me-3-NIT-Pyz = 2-[3-(1-methyl-pyrazolyl)]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; hfac = hexafluoroacetylacetone). Single crystal X-ray diffraction studies showed that all three complexes are composed of two independent mononuclear bi-spin systems, in which the central LnIII ions are eight-coordinated with three bidentate hfac− ions and one bidentate chelating 1-Me-3-NIT-Pyz radical. The coordination polyhedron of the central LnIII ions can be described as a triangular dodecahedron (D2d). In addition, there exist weak ferromagnetic couplings in the GdIII-NIT radical system in complex 1 based on magnetic fitting. Dynamic magnetic studies show that the out-of-phase component of the ac-magnetic susceptibilities of complexes 2 and 3 exhibit a certain degree of frequency dependence and the two complexes do not show any obvious magnetic relaxation behavior.

Syntheses and Crystal Structures of Two Classes of Aluminum-Lanthanide-Sodium Heterotrimetallic 12-Metallacrown-4 Compounds: Individual Molecules and Dimers of Metallacrowns

Two series of aluminum-lanthanide-sodium 12-metallacrown-4 compounds have been synthesized and characterized by single-crystal X-ray analysis. For the individual LnNa(ben)4[12-MCAl(III)N(shi)-4] molecules, where LnIII = Eu (1), Gd (2), Tb (3), Dy (4), Ho (5), Er (6), Tm (7), Yb (8), Lu (9), and Y (10), ben− is benzoate, MC is metallacrown, and shi3− is salicylhydroximate, two independent molecules are present in each unit cell. The aluminum(III) ions and shi3− ligands comprise the MC framework, while the LnIII and Na+ ions bind opposite of each other across the central MC cavity. The benzoate anions serve to tether the LnIII ion to the MC framework. When benzoate is replaced with the dicarboxylate anion isophthalate (iph2−), two [12-MCAl(III)N(shi)-4] units are connected to form a dimer of MCs: {LnNa[12-MCAl(III)N(shi)-4]}2(iph)4, where LnIII = Eu (11), Gd (12), Tb (13), Dy (14), Ho (15), Ho (16), Er (17), Yb (18), and Lu (19). As in 1–10, the aluminum(III) ions and shi3− ligands produce the MC frameworks, and one LnIII ion binds to each central MC cavity. However, there are two binding modes for the sodium ions. For 12–15 and 18, the sodium ions bind to the central MC cavity opposite of the LnIII ions as in 1–10. For 11, 16, 17, and 19, the sodium ions bind to the side of the MC framework by bonding to the phenolate and carboxylate oxygen atoms of two shi3− ligands and to the carboxylate oxygen atom of an iph2− ligand. In these structures, the MC cavity is vacant opposite of the LnIII ions. The substitution of isophthalate for benzoate does not significantly alter the [12-MCAl(III)N(shi)-4] framework as the size of the central MC cavity is not significantly different between analogous lanthanide individual and dimer MCs. However, the identity of the central LnIII ion does determine how close the LnIII ion can approach the mean plane of the oxime oxygen atoms (OoxMP) of the MC cavity. As the ion radius of the central LnIII ion decreases, the LnIII ion is able to more closely approach the OoxMP. For the individual MCs 1–10, the EuIII of 1 is the farthest away from the OoxMP (1.55 A) and this value steadily decreases to 1.44 A for the LuIII ion of 9. This same trend is true for the dimer MCs as the EuIII ion of 11 is 1.45 A from the OoxMP and the LuIII ion of 19 is 1.36 A from the OoxMP. Though the location of the sodium ions in the dimer MCs does influence the LnIII-OoxMP distance as the absence of the sodium ion in the MC cavity allows the LnIII ion to approach the MC cavity even closer. In 15 a sodium ion is opposite the HoIII ion and the HoIII-OoxMP distance is 1.47 A, while in 16 the sodium ion is bound to the side of the MC and the HoIII-OoxMP distance is 1.40 A. The complex GdNa[12-MCAl(III)N(shi)-4]}2(iph)4(DMF)2(H2O)8 is a dimer of [12-MC-4] molecules linked by four isophthalate anions.

Luminescence of Lanthanide Complexes with Perfluorinated Alkoxide Ligands.

Four groups of rare-earth complexes, comprising 11 new compounds, with fluorinated O-donor ligands ([K(THF)6][Ln(OC4F9)4(THF)2] (1-Ln; Ln = Ce, Nd), [K](THF)x[Ln(OC4F9)4(THF)y] (2-Ln; Ln = Eu, Gd, Dy), [K(THF)2][Ln(pinF)2(THF)3] (3-Ln; Ln = Ce, Nd), and [K(THF)2][Ln(pinF)2(THF)2] (4-Ln; Ln = Eu, Gd, Dy, Y) have been synthesized and characterized. Single-crystal X-ray diffraction data were collected for all compounds except 2-Ln. Species 1-Ln, 3-Ln, and 4-Ln are uncommon examples of six-coordinate (Eu, Gd, Dy, and Y) and seven-coordinate (Ce and Nd) LnIII centers in all-O-donor environments. Species 1-Ln, 2-Ln, 3-Ln, and 4-Ln are all luminescent (except where Ln = Gd and Y), with the solid-state emission of 1-Ce being exceptionally blue-shifted for a Ce complex. The emission spectra of the six Nd, Eu, and Dy complexes do not show large differences based on the ligand and are generally consistent with the well-known free-ion spectra. Time-dependent density functional theory results show that 1-Ce and 3-Ce undergo allowed 5f → 4d excitations, consistent with luminescence lifetime measurements in the nanosecond range. Eu-containing 2-Eu and 4-Eu, however, were found to have luminescence lifetimes in the millisecond range, indicating phosphorescence rather than fluorescence. The performance of a pair of multireference models for prediction of the Ln = Nd, Eu, and Dy absorption spectra was assessed. It was found that spectroscopy-oriented configuration interaction as applied to a simplified model in which the free-ion lanthanide was embedded in ligand-centered Löwdin point charges performed as well (Nd) or better (Eu and Dy) than canonical NEVPT2 calculations, when the ligand orbitals were included in the treatment.

Trinuclear NiII-LnIII-NiII Complexes with Schiff Base Ligands: Synthesis, Structure, and Magnetic Properties.

The reaction of the Schiff base ligand o-OH-C6H4-CH=N-C(CH2OH)3, H4L, with Ni(O2CMe)2·4H2O and lanthanide nitrate salts in a 4:2:1 ratio lead to the formation of the trinuclear complexes [Ni2Ln(H3L)4(O2CMe)2](NO3) (Ln = Sm (1), Eu (2), Gd (3), Tb (4)). The complex cations contain the strictly linear NiII-LnIII-NiII moiety. The central LnIII ion is bridged to each of the terminal NiII ions through two deprotonated phenolato groups from two different ligands. Each terminal NiII ion is bound to two ligands in distorted octahedral N2O4 environment. The central lanthanide ion is coordinated to four phenolato oxygen atoms from the four ligands, and four carboxylato oxygen atoms from two acetates which are bound in the bidentate chelate mode. The lattice structure of complex 4 consists of two interpenetrating, supramolecular diamond like lattices formed through hydrogen bonds among neighboring trinuclear clusters. The magnetic properties of 1–4 were studied. For 3 the best fit of the magnetic susceptibility and isothermal M(H) data gave JNiGd = +0.42 cm−1, D = +2.95 cm−1 with gNi = gGd = 1.98. The ferromagnetic nature of the intramolecular Ni···Gd interaction revealed ground state of total spin S = 11/2. The magnetocaloric effect (MCE) parameters for 3 show that the change of the magnetic entropy (−ΔSm) reaches a maximum of 14.2 J kg−1 K−1 at 2 K. A brief literature survey of complexes containing the NiII-LnIII-NiII moiety is discussed in terms of their structural properties.

Pentanuclear Spirocyclic Ni4Ln Derivatives: Field Induced Slow Magnetic Relaxation in the Dysprosium and Erbium Analogues

Five pentanuclear heterometallic isostructural complexes, [Ni4Ln(L)2(LH)2(CH3CN)3Cl]·xH2O·yCH3OH {Ln = YIII (1), GdIII (2), TbIII (3), DyIII (4) and ErIII (5)} [for 1 and 2, x = 2, y = 1; for 3, x = 6, y = 2; for 4, x = 5, y = 1; for 5, x = 2, y = 2] were prepared by the reaction of (E)‐2‐(hydroxymethyl)‐6‐{[(2‐hydroxyphenyl)imino]methyl}‐4‐methylphenol (LH3) with LnCl3·6H2O and Ni(OAc)2·4H2O in the presence of tetrabutylammonium hydroxide (TBA‐OH) base. The structural characterization reveals that compounds 1–5 contain a spirocyclic pentanuclear core [Ni4Ln(µ3‐O)4(µ2‐O)4]3+ where two triangular motifs [Ni2Ln(µ3‐O)2(µ2‐O)2]3+ are fused together through a common vertex of the LnIII ion. The central LnIII ion forms an eight‐coordinated distorted triangular dodecahedron geometry, while the nickel(II) ions form a distorted octahedron geometry. Comprehensive dc magnetic studies reveal that antiferromagnetic exchange interaction exists between the NiII centres. The ac susceptibility measurement revels that dysprosium and erbium analogue shows field induced slow magnetic relaxation with an anisotropic barrier (Ueff) of 25.12 cm–1 and 22.13 cm–1 respectively.