Mononuclear Lanthanide Research Articles

Synthesis, characterisation and liquid crystalline behaviour of some lanthanides complexes containing two azobenzene Schiff base

Schiff base ligand N,N′-di-(4-butylsalicylidene)-1′,3′-diaminopropane [H2L] was synthesised by the reaction of substituted azobenzene and 1,3-diaminopropane in 2:1 molar ratio. Four mononuclear lanthanide complexes of the type [Ln(H2L)LCl] (Ln = LaIII, CeIII, SmIII and GdIII) were synthesised and characterised by 1H,13C NMR, fourier transform infrared (FT-IR) spectroscopy, elemental analysis (CHNO), gas chromotography-mass, magnetic susceptibility and molar conductivity. Thermal properties of the title compounds were studied using the thermogravimetric analysis/differential scanning calorimetry (TGA/DSC) and optical polarising microscopy (OPM). The ligand and coordination compounds exhibit liquid-crystalline properties (smectic A).

A series of mononuclear lanthanide complexes featuring 3-D supramolecular networks: synthesis, characterization and luminescent properties for sensing guest molecules

A new series of four isostructural mononuclear lanthanide complexes Ln(HPDH)3(H2O)3·H2O (Ln = Sm(III) 1, Eu(III) 2, Tb(III) 3 and Dy(III) 4; H2PDH = 6,7-dihydropyrido(2,3-d)pyridazine-5,8-dione) has been prepared and characterized by IR, elemental analysis, XRD and TG-DTA methods. Single crystal X-ray diffraction analysis of both complexes 1 and 3 revealed that the mononuclear discrete complexes form 3-D supramolecular networks via hydrogen bonds and offset stacking (–H···π) interactions. The photoluminescence study of the title complexes revealed the photoluminescent potential of the antenna ligand (H2PDH) toward the concerned lanthanide cations. The luminescence based sensing ability of the partially dehydrated complex Tb(HPDH)3(H2O)33a towards small solvent molecules, along with its reusability, has been studied. Isopropyl alcohol was found to be an excellent sensitizer, while tetrahydrofuran was a highly quenching solvent with a first order behavior towards the photoluminescence intensity. The photoluminescence intensity was found to decrease with the increase of the dielectric constant and normalized Dimroth–Reichardt ET parameter values for protic solvents, while reverse behavior was observed for dipolar aprotic solvents.

Urothermal synthesis of mononuclear lanthanide compounds: slow magnetization relaxation observed in Dy analogue

Two mononuclear compounds Ln(e-urea)8(NO3)3 (Ln = Dy(1) and Tb(2)) have been urothermally synthesized by using the ethyleneurea (e-urea) as an organic ligand and a solvent. The e-urea ligand with a single donor atom is a unique ligand for coordinating to lanthanide ions, which is very different from those commonly observed polytopic ligands with suitable coordination pockets to encapsulate lanthanide(III) ions or chelating organic ligands. The lanthanide center surrounded by eight e-urea ligands is in a square antiprismatic environment with an approximate D4d local symmetry. Magnetic properties of both compounds have been investigated in detail using direct-current and alternating-current susceptibility measurements. The Dy(1) analogue displays slow magnetic relaxation behavior with an effective energy barrier of the magnetic relaxation of 37.68 K and the pre-exponential factor τ0 of 1.47 × 10−9 s in the presence of direct-current field of 2 kOe.

ChemInform Abstract: Lessons Learned from Dinuclear Lanthanide Nano‐Magnets

AbstractReview: about 50 refs.

Slow Magnetic Relaxation in a Hydrogen-Bonded 2D Array of Mononuclear Dysprosium(III) Oxamates

The reaction of N-(2,6-dimethylphenyl)oxamic acid with dysprosium(III) ions in a controlled basic media afforded the first example of a mononuclear lanthanide oxamate complex exhibiting a field-induced slow magnetic relaxation behavior typical of single-ion magnets (SIMs). The hydrogen-bond-mediated self-assembly of this new bifunctional dysprosium(III) SIM in the solid state provides a unique example of 2D hydrogen-bonded polymer with a herringbone net topology.

Lessons learned from dinuclear lanthanide nano-magnets

The quest for higher density information storage has led to the investigation of Single-Molecule Magnets (SMMs) as potential molecules to be applied in materials such as hard discs. In order for this to occur, one must first design metal complexes which can retain magnetic information at temperatures where these applications become possible. This can only be achieved through answering and understanding fundamental questions regarding the observed physical properties of SMMs. While mononuclear lanthanide complexes have shown promise in obtaining high energy barriers for the reversal of the magnetisation they are limited to Single-Ion Magnet behaviour intrinsic to one metal centre with a limited number of unpaired electrons. As a way of increasing the effective anisotropic barrier, systems with higher nuclearity have been sought to increase the spin ground state of the molecule. Dinuclear complexes are presented as key compounds in studying and understanding the nature of magnetic interactions between metal ions. This tutorial review will span a number of dinuclear 4f complexes which have been critical in our understanding of the way in which lanthanide centres in a complex interact magnetically. It will examine key bridging moieties from the more common oxygen-based groups to newly discovered radical-based bridges and draw conclusions regarding the most effective superexchange pathways allowing the most efficient intracomplex interactions.

Mononuclear lanthanide complexes incorporating an anthracene group: structural modification, slow magnetic relaxation and multicomponent fluorescence emissions in Dy compounds

Four mononuclear lanthanide complexes, [Ln(hfac)3(depma)(H2O)] [Ln(III) = Dy (1), Gd (2)], [Dy(hfac)3(depma)2]2·H2O (3) and [Gd(hfac)3(depma)2]·2H2O (4), have been obtained (hfac = hexafluoroacetylacetonate, depma = 9-diethylphosphonomethyl anthracene) by using one (for 1 and 2) or two (for 3 and 4) depma molecules to substitute coordination water molecules of Ln(hfac)3(H2O)2. It was found that the number of introduced depma ligands can modify the coordination geometry of Ln(iii) ions, showing a distorted biscapped triangular prism geometry in isostructural 1 and 2 and a distorted square-antiprismatic geometry in 3 and 4. Magnetic studies reveal that both 1 and 3 show field-induced slow magnetic relaxation under the applied dc field of 1000 Oe. The solid-state fluorescence measurements indicate the presence of multicomponent emissions in 1 and 3, including ligand-centered (LC) emissions from hfac and depma, and yellow emission from Dy(III) ions and only ligand-centered (LC) emissions in 2 and 4.

New polyoxometalate-based mononuclear lanthanide complexes with slow relaxation of magnetization

A series of new polyoxometalate(POM)-based mononuclear lanthanide(III)–bi pyridine-N-oxide complexes, [Ln(bpyno)4][PMo12O40]·2H2O (Ln=Dy (1), Tb (2), Er (3), Ho (4); bpyno=4,4′-dimethyl-2,2′-bipyridyl-N-N′-dioxide), have been synthesized by the reactions between LnPMo12O40 salts (Ln=Dy (1), Tb (2), Er (3), Ho (4)) and bpyno ligand. All compounds were characterized by elemental analyses, TG analyses, IR, powder X-ray diffraction and single-crystal X-ray diffraction. In 1–4, each mononuclear Ln center is coordinated by eight O atoms derived from four bpyno ligands, exhibiting an approximate square antiprismatic coordination geometry. Furthermore, the [Ln(bpyno)4]3+ units are well separated by the α-Keggin-type polyoxoanions. Magnetic measurements indicate that compound 1 exhibits frequency dependent ac magnetic susceptibilities indicative of slow relaxation of the magnetization.

DyIII‐ and YbIII‐Curcuminoid Compounds: Original Fluorescent Single‐Ion Magnet and Magnetic Near‐IR Luminescent Species

The multifunctional behavior of two mononuclear lanthanide compounds attached to a curcuminoid called 9 Accm has been investigated. The results show that [Dy(9 Accm)(2)(NO(3))(dmf)(2)] Yb(9 Accm)(3)(py)] behaves as a single-ion magnet and that both compounds display luminescent responses and exhibit affinity for graphite surfaces (see figure).

Field-induced slow magnetic relaxation in chiral seven-coordinated mononuclear lanthanide complexes

Four couples of enantiomerically pure chiral seven-coordinated mononuclear lanthanide complexes, [(L(OEt))Dy((R,R)-Salphen)](2)·3H(2)O (1, L(OEt) = [(Cp)Co(P(O)(OEt)(2))(3)], Cp = cyclopentadiene, Salphen = N,N'-1,2-diphenylethylenebis(salicylideneiminato) dianion), [(L(OEt))Dy((S,S)-Salphen)](2)·3H(2)O (2), [(L(OEt))Dy((R,R)-5-Cl-Salcy)]·CH(3)OH·1/8H(2)O (3, Salcy = N,N'-(1,2-cyclohexanediylethylene)bis(salicylideneiminato) dianion), [(L(OEt))Dy((S,S)-5-Cl-Salcy)]·CH(3)OH·1/8H(2)O (4), [(L(OEt))Tb((R,R)-5-Cl-Salcy)]·CH(3)OH·1/8H(2)O (5), [(L(OEt))Tb((S,S)-5-Cl-Salcy)]·CH(3)OH·1/8H(2)O (6), [(L(OEt))Ho((R,R)-5-Cl-Salcy)]·CH(3)OH·1/8H(2)O (7) and [(L(OEt))Ho((S,S)-5-Cl-Salcy)]·CH(3)OH·1/8H(2)O (8), have been successfully synthesized by using tetradentate chiral salen-type ligands and the Kläui's tripodal ligand of L(OEt). Structural analyses reveal that all compounds have a typical double-decker sandwich structure, and the Ln(iii) ions exhibit a rare seven-coordinated mode, situating in a distorted monocapped triangular prism polyhedron. Circular dichroism (CD) spectra confirm the enantiomeric nature of the optically active complexes and demonstrate that the chirality is successfully transferred from the ligand to the coordination environment of the Ln(iii) ions. Field-induced slow relaxation of the magnetization is observed for complexes 1-4, suggesting that they can be rare chiral single-ion magnets (SIMs) based on the seven-coordinated lanthanide ions.

Hydrothermal Synthesis, Structural Determination, and Properties of a New Family of Mononuclear Lanthanide Complexes with Pyridines Bearing More Flexible Pendant-Arm Carboxylate Substituents

Members of a new family of mononuclear lanthanide complexes possessing the general formula Ln(3-pyrac)3(H2O)3 (Ln = Y 1, La 2, Sm 3, Eu 4, Gd 5, Tb 6, Dy 7, Er 8, 3-pyrac = 3-pyridylacetate) were synthesized by hydrothermal reaction and characterized by single-crystal x-ray diffraction analysis, infrared (IR) spectra, luminescent spectroscopy, and thermal analysis. Photoluminescence measurement indicates that the complexes 3, 4, 6, and 7 exhibit characteristic emission of Sm(III), Eu(III), Tb(III), and Dy(III) at room temperature. The electrochemical behavior of complexes 4 has been examined by cyclic voltammetry in aqueous solution.

From Discrete Molecule to One‐Dimension Chain: Two New Nitronyl Nitroxide–Lanthanide Complexes Exhibiting Slow Magnetic Relaxation

AbstractA mononuclear lanthanide–radical complex [Tb(hfac)3(NITPhSCH3)2] (1) and a one‐dimensional chain complex [Tb(hfac)3(NITPhSCH3)]n (2) {hfac = hexafluoroacetylacetonate, NITPhSCH3 = 2‐[4‐(methylthio)phenyl]‐4,4,5,5‐tetramethylimidazolin‐1‐oxyl 3‐oxide} have been synthesized. Single‐crystal X‐ray diffraction studies revealed that compound 1 is a mononuclear complex in which two NITPhSCH3 radicals are coordinated as monodentate ligands to the TbIII ion through their NO groups to form a tri‐spin complex, and complex 2 is a 1D chain structure constructed of Tb(hfac)3 units bridged by NITPhSCH3 radicals through their NO groups. The temperature dependence of the magnetic susceptibilities of 1 and 2 indicates ferromagnetic coupling between the TbIII ion and the NITPhSCH3 radical. Frequency‐dependent out‐of‐phase signals of alternating current magnetic susceptibilities were observed at low temperature for both complexes, indicative of slow magnetic relaxation.

Enantiomeric Self-Recognition in Homo- and Heterodinuclear Macrocyclic Lanthanide(III) Complexes

The controlled formation of lanthanide(III) dinuclear μ-hydroxo-bridged [Ln(2)L(2)(μ-OH)(2)X(2)](n+) complexes (where X = H(2)O, NO(3)(-), or Cl(-)) of the enantiopure chiral macrocycle L is reported. The (1)H and (13)C NMR resonances of these complexes have been assigned on the basis of COSY, NOESY, TOCSY, and HMQC spectra. The observed NOE connectivities confirm that the dimeric solid-state structure is retained in solution. The enantiomeric nature of the obtained chiral complexes and binding of hydroxide anions are reflected in their CD spectra. The formation of the dimeric complexes is accompanied by a complete enantiomeric self-recognition of the chiral macrocyclic units. The reaction of NaOH with a mixture of two different mononuclear lanthanide(III) complexes, [Ln(1)L](3+) and [Ln(2)L](3+), results in formation of the heterodinuclear [Ln(1)Ln(2)L(2)(μ-OH)(2)X(2)](n+) complexes as well as the corresponding homodinuclear complexes. The formation of the heterodinuclear complex is directly confirmed by the NOESY spectra of [EuLuL(2)(μ-OH)(2)(H(2)O)(2)](4+), which reveal close contacts between the macrocyclic unit containing the Eu(III) ion and the macrocyclic unit containing the Lu(III) ion. While the relative amounts of homo- and heterodinuclear complexes are statistical for the two lanthanide(III) ions of similar radii, a clear preference for the formation of heterodinuclear species is observed when the two mononuclear complexes contain lanthanide(III) ions of markedly different sizes, e.g., La(III) and Yb(III). The formation of heterodinuclear complexes is accompanied by the self-sorting of the chiral macrocyclic units based on their chirality. The reactions of NaOH with a pair of homochiral or racemic mononuclear complexes, [Ln(1)L(RRRR)](3+)/[Ln(2)L(RRRR)](3+), [Ln(1)L(SSSS)](3+)/[Ln(2)L(SSSS)](3+), or [Ln(1)L(rac)](3+)/[Ln(2)L(rac)](3+), results in mixtures of homochiral, homodinuclear and homochiral, heterodinuclear complexes. On the contrary, no heterochiral, heterodinuclear complexes [Ln(1)L(RRRR)Ln(2)L(SSSS)(μ-OH)(2)X(2)](n+) are formed in the reactions of two different mononuclear complexes of opposite chirality.

Acylpyrazolonate-based lanthanide complexes: Synthesis, crystal structures and photoluminescence properties

Two new acylpyrazolonate-based lanthanide complexes of formula [Ln(pmap) 3(H 2O) 2]·CH 3COOC 2H 5 (Ln = Tb 1, Eu 2 and pmap = 1-phenyl-3-methyl-4-acetyl-5-pyrazolonate) have been prepared and characterized by X-ray single crystal determination and spectroscopic methods. The crystal structure analysis reveals that 1 and 2 are isostructural and crystallize in the triclinic space group P 1 ¯ with two independent, but structurally similar molecules in the structural unit, which are exceptionally rare in acylpyrazolonate-based mononuclear lanthanide complexes. In CH 3CN solution, the photoluminescence investigation demonstrates that 1 displays intensely green emission of Tb(III)-centered, while Eu(III)-complex does not emit characteristically red luminescence. The results are elucidated in terms of the energy gap Δ E( 3ππ*– 5D 4 or 5D 0) between Hpmap ligand and resonance levels of Tb(III) or Eu(III) ion.

Novel photoluminescent lanthanidomesogens forming bilayer smectic phase derived from blue light emitting liquid crystalline, one ring O-donor Schiff-base ligands

A series of new mononuclear lanthanide(III)-salicylaldimine complexes of the type [Ln(LH) 3(NO 3) 3] (Ln = La, Pr, Sm and Gd; LH = N-(2-hydroxyethyl)-4 n-alkoxysalicylaldimine, n = 14, 18) have been synthesized and characterized by FT-IR, 1H NMR, 13C NMR, UV–Vis, FAB-mass and magnetic susceptibility measurements. The ligand (LH) coordinate to lanthanide ions in zwitterionic form via the phenolic-oxygen with the proton shifted to the imine–nitrogen. The nitrato groups occurring in chelated bidentate fashion complete a nine-coordinate geometry. Polarized optical microscopy (POM) and differential scanning calorimetry (DSC) show that the ligands are monotropic and their complexes exhibit enantiotropic highly viscous smectic A (SmA) mesophase in the temperature range 60–185 °C. A bilayer self organized assembly of the molecules in the mesophase are proposed on the basis of the small angle XRD study. The ligands are blue light emitters with a broad emission maxima at ∼447 nm while the lanthanide complexes show intense emission in the visible range (∼465–679 nm) at 350 nm excitation. The samarium(III) complex, [Sm(LH) 3(NO 3) 3] is distinct from the rest in emitting bright orange light (∼660 nm, Φ = 48%). The S o–S 1 excitation band being stronger than the direct f–f excitation in the samarium complex clearly suggests that the Schiff-base ligands efficiently sensitize the luminescence of Sm 3+. DFT calculations have been performed using DMol3 program at BLYP/DNP level to obtain the stable electronic structure of the ligand and complex.

A series of new hybrid compounds constructed from Dawson-type phosphomolybdates and metal–organic coordination complexes

In this study, a series of compounds based on Dawson-type phosphomolybdates, H3(C6NO2H6)2[K(H2O)3(C6NO2H5)3][P2Mo18O62] ⋅ 5.5H2O (1), (C6NO2H6)6[Ln(H2O)7(C6NO2H5)2]2[P2Mo18O62]2·13.5H2O (Ln = Ce (2), La (3)) have been synthesized and characterized by elemental analysis, IR and UV-Vis spectroscopy methods, TG analysis, and single-crystal X-ray diffraction. Compound 1 consists of [P2Mo18O62]6− building units joined by potassium-pyridine-3-carboxylic acid complexes, resulting in a wavelike polyoxometalate (POM) chain, which further interacts with each other via intermolecular interactions to form a 3-D supramolecular channel framework containing guest water molecules. Compounds 2 and 3 possess a 3-D supramolecular framework with 1-D tunnel constructed from [P2Mo18O62]6− and mononuclear lanthanide coordination complex fragments. To the best of our knowledge, 1 not only represents the first example of 1-D hybrid assembly based on Dawson-type phosphomolybdate, but also the first hybrid compound constructed from Dawson-type POMs and alkali–metal coordination complex fragments.

Syntheses, crystal structures and properties of a new family of isostructural and isomorphous compounds of type [M(L)(NCS) 3] [M = La, Gd, Tb and Dy; L = a neutral hexadentate Schiff base

The neutral hexadentate Schiff base N-(1-pyridin-2-yl-phenylidene)-N′-[2-({2-[(1-pyridin-2-yl-phenylidene)amino]ethyl}amino)ethyl]ethane-1,2-diamine (L) was used to synthesize new lanthanide(III) complexes of type [M(L)(NCS) 3] (M = La, 1; Gd, 2; Tb, 3; Dy, 4). Single crystal X-ray diffractometry reveals the tricapped trigonal prismatic structure of all the compounds. Variable-temperature magnetic susceptibility measurements in 2– 4 show the expected χ M T versus T plot for an isolated, mononuclear lanthanide(III) ion with 4f 7, 4f 8 and 4f 9 configurations, respectively following Curie Law.

Correlations between structure and magnetism of three N,N′-ethylene-bis(3-methoxysalicylideneimine) gadolinium complexes

Three Salen-like gadolinium complexes, namely, mononuclear (4f) complex [{H 2 L}Gd(NO 3 ) 3 ] ( 1 ), heterodinuclear (3d–4f) complex [{LCu}Gd(NO 3 ) 3 ]·0.25H 2 O ( 2 ) and dimeric heterotrinuclear (3d–4f–3d′) complex [{LCu}Gd(H 2 O) 3 {Fe(CN) 6 }] 2 ·6H 2 O ( 3 ) [H 2 L = N , N ′-ethylene-bis(3-methoxysalicylideneimine)] have been synthesized by stepwise reactions. X-ray diffraction analysis reveals that 1 is of a discrete structure in which H 2 L coordinates to gadolinium ion through O 2 O 2 moiety. Then, addition of Cu(Ac) 2 ·H 2 O to the mononuclear lanthanide complex yields expected heterodinuclear (3d–4f) complexes [{LCu}Gd(NO 3 ) 3 ]. 3 features a unique 1D ladder-like topology structure through the intermolecular double links of Cu–N bonds. The measurement of variable-temperature magnetic susceptibility reveals that complex 1 exhibits antiferromagnetic interaction while 2 and 3 exhibit ferromagnetic interaction between spin carriers. The correlations between the structure and magnetism are described and discussed.

Single-ion magnets based on mononuclear lanthanide complexes with chiral Schiff base ligands [Ln(FTA)3L] (Ln = Sm, Eu, Gd, Tb and Dy)

A series of mononuclear lanthanide complexes with chiral Schiff base ligands [Ln(FTA)(3)L] [Ln = Dy(1), Sm(2), Eu(3), Gd(4), and Tb(5), L = (S,S)-2,2'-Bis(4-benzyl-2-oxazoline)] were synthesized and characterized. Among these complexes, complex 1 represents the first example of mononuclear lanthanide complexes displaying single-ion magnet behavior and ferroelectricity.

A Polynuclear Lanthanide Single‐Molecule Magnet with a Record Anisotropic Barrier

Single-molecule magnets (SMMs) continue to be an attractive research field because of their unique and intriguing properties and potential applications in high-density data storage technologies and molecular spintronics. The anisotropic barrier (U) of an SMM is derived from a combination of an appreciable spin ground state (S) and uniaxial Ising-like magneto-anisotropy (D). The magnet-like behavior can be observed by slow relaxation of the magnetization below the blocking temperature. Since the discovery of SMMs in the early 1990s, this assumption has formed the basis for the understanding of the origin of the anisotropic barrier. However, in recent years the development of novel lanthanide-only SMMs that challenge and defy this theory pose a number of questions: How can slow relaxation of the magnetization be observed in a nonmagnetic state complex? Why are large energy barriers seen for mononuclear lanthanide(III) complexes? To answer such important questions, it is vital to investigate novel SMMs with high magnetoanisotropy for which the influence of the large negative D value could result in higher anisotropic barriers. Clearly lanthanide-based polynuclear systems are an important avenue to explore in the pursuit of SMMs with higher anisotropic barriers, because of the strong spin–orbit coupling commonly observed in 4f systems. However, lanthanide-only SMMs are rare. The majority of reported SMMs have been prepared with transition-metal ions, although the recent application of a mixed transition-metal/ lanthanide strategy also yielded many structurally and magnetically interesting systems. The scarcity of lanthanide-only SMMs results from the difficulty in promoting magnetic interactions between the lanthanide ions. The interactions can, however, be enhanced by overlapping bridging ligand orbitals. In addition, fast quantum tunneling of the magnetization (QTM), which is common for lanthanide systems, generally prevents the isolation of SMMs with high anisotropic energy barriers. Our recent work suggests that dysprosium(III) ions may hold the key to obtaining high-blocking-temperature lanthanide-only SMMs. When an appropriate ligand system is employed, it is possible to exploit the large intrinsic magnetoanisotropy, high spin, and reduced QTM that dysprosium(III) ions offer. Recently, we have focused our attention towards the synthesis of dysprosium(III) cluster complexes with 1,2bis(2-hydroxy-3-methoxybenzylidene) hydrazone (H2bmh) and 3-methoxysalicylaldehyde hydrazone (Hmsh) as chelating agents (see Figure S1 in the Supporting Information). This strategy has proven to be successful and has led to a polynuclear lanthanide SMM with a record anisotropic barrier. Herein, we report the synthesis, structure, and magnetism of a tetranuclear dysprosium(III) SMM that exhibits the largest relaxation barrier seen for any polynuclear SMM to date. A suspension of DyCl3·6H2O and o-vanillin (2:1 ratio) in DMF/CH2Cl2 (1:5 ratio) was treated with 4 equivalents of Et3N. The solution was stirred for 1 minute, and then 4 equivalents of N2H4·H2O was added. The resulting yellow solution yielded rectangular, orange-yellow crystals of the tetranuclear complex [Dy4(m3-OH)2(bmh)2(msh)4Cl2] (1) in 19.1% yield after 2 days. The msh and bmh ligands were formed in situ by the reaction of o-vanillin and hydrazine. The slight excess of hydrazine is essential for the formation of both ligands; when an excess of o-vanillin was used instead, no product was isolated. The basic conditions promote the deprotonation of the ligands and the formation of bridging hydroxide anions. Single-crystal X-ray analysis revealed the centrosymmetric complex 1 (Figure 1), which has a defect-dicubane central core. The four coplanar Dy ions are bridged by two m3-OH ligands displaced above and below (0.922 ) the Dy4 plane with Dy O bond lengths of 2.362(6), 2.302(6), and 2.447(6) andDy O Dy angles of 106.5(2), 107.7(2), and 105.7(2)8, and also by a combination of four phenoxide oxygen atoms [Dy O 2.312(2), 2.298(6), 2.448(6), 2.345(6) ] and two diaza bridging groups [Dy N 2.508(8), 2.564(8) ]. Close inspection of the packing arrangement reveals stacking of the [*] P.-H. Lin, Dr. T. J. Burchell, Dr. M. Murugesu Chemistry Department, University of Ottawa and Centre for Catalysis Research and Innovation D’Iorio Hall, 10 Marie Curie, Ottawa, ON, K1N6N5 (Canada) Fax: (+1)613-562-5170 E-mail: m.murugesu@uottawa.ca Homepage: http://www.science.uottawa.ca/~mmuruges/