Dy Derivatives Research Articles

Two dysprosium complexes based on TEMPO radical derivative: synthesis, structures, magnetic and fluorescent properties

A new TEMPO derivative was synthesized and two Dy-radical complexes, [Dy(hfac)3(H2O)hmb-TEMPO] (1) and [Dy(hfac)3(hmb-TEMPO)2] (2, hmb-TEMPO = 4-((2-hydroxy-3-methoxybenzylidene)amino)-2,2,6,6-tetramethyl; hfac = hexafluoroacetylacetonate), were synthesized through reacting hmb-TEMPO radical and Dy(hfac)3 with 1:1 and 1:2 ratio, respectively. The structures of 1 and 2 were elucidated by single-crystal X-ray structural analysis. Both 1 and 2 feature mononuclear structures. Nonzero out-of-phase signals were observed for both Dy derivatives, indicating single-molecule magnet behavior. The room-temperature photoluminescence spectra of 1 and 2 exhibit strong emissions in the visible region.

Regulating Magnetic Relaxation of Radical-Ln-Based Chains Involving Multidentate Nitronyl Nitroxides through Varying Spin Arrangement Motif and Local Symmetry around Ln Centers

The reaction of a newly designed multidentate nitronyl nitroxide radical NIT-Ph-3,5-b-3PyO with Ln(hfac)3·2H2O led to two new 2p–4f chains {[Ln(hfac)3]2(NIT-Ph-3,5-b-3PyO)}n (LnIII = GdIII 1, DyIII 2; NIT-Ph-3,5-b-3PyO = 2-[3,5-bis(3-pyridinyloxy)-phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide). When the Cu(hfac)2 was introduced in the above reaction, the hetero-tri-spin 2p–3d–4f chains {Ln(hfac)3[Cu(hfac)2]2(NIT-Ph-3,5-b-3PyO)2}n (LnIII = GdIII 3, DyIII 4) were obtained. The crystal data show that the {4f–2p–4f} spin motif is involved in 2p–4f chains, while the {2p–4f–2p} arrangement of spins around Ln centers is found in 2p–3d–4f chains. Direct-current magnetic susceptibility investigations show that both Gd chains display the dominant GdIII–NO ferromagnetic exchanges. Alternating-current susceptibilities prove the existence of the field-induced slow magnetic relaxation behavior in 2, while no nonzero χ″ signals are observed for 4, which could be attributed to the distinct magnetic exchanges originated from different spin arrangements (4f–2p–4f versus 2p–4f–2p) and the different coordination geometry around the DyIII ions for two Dy derivatives (D4d of Dy1 center in 2 and D2d in 4).

Cyclic [Cu-biRadical]2 Secondary Building Unit in 2p-3d and 2p-3d-4f Complexes: Crystal Structure and Magnetic Properties.

Employing the new nitronyl nitroxide biradical ligand biNIT-3Py-5-Ph (2-(5-phenyl-3-pyridyl)-bis(4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide)), a 16-spin Cu-radical complex, [Cu8(biNIT-3Py-5-Ph)4(hfac)16] 1, and three 2p-3d-4f chain complexes, {[Ln(hfac)3][Cu(hfac)2]2(biNIT-3Py-5-Ph)2}n (LnⅢ= Gd 2, Tb 3, Dy 4; hfac = hexafluoroacetylacetonate), have been prepared and characterized. X-ray crystallographic analysis revealed in all derivatives a common cyclic [Cu-biNIT]2 secondary building unit in which two bi-NIT-3Py-5-Ph biradical ligands and two CuII ions are associated via the pyridine N atoms and NO units. For complex 1, two such units assemble with four additional CuII ions to form a discrete complex involving 16 S = 1/2 spin centers. For complexes 2-4, the [Cu-biNIT]2 units are linked by LnIII ions via NO groups in a 1D coordination polymer. Magnetic studies show that the coordination of the aminoxyl groups with Cu or Ln ions results in behaviors combining ferromagnetic and antiferromagnetic interactions. No slow magnetic relaxation behavior was observed for Tb and Dy derivatives.

Controlled Hydrolysis of Phosphate Esters: A Route to Calixarene-Supported Rare-Earth Clusters.

Phosphate ester bonds are widely present in nature (e. g. DNA/RNA) and can be extremely stable against hydrolysis without the help of catalysts. Previously, we showed how the combination of phosphoryl and calix[4]arene moieties in the same organic framework (LPO ) allows isolation of single lanthanide (Ln) metal ions as [LnIII (LPO )2 ](O3 SCF3 )3 . Here we report how by controlling the reaction conditions a new hydrolyzed phosphoryl-calix[4]arene ligand (H3 LHPO ) is formed as a result of LnIII -mediated P-OEt bond cleavage in three out of the eight possible sites in LPO . The chelating nature of H3 LHPO traps the LnIII species in the form of [LnIII (LHPO )((EtO)2 P(O)OH)]2 dimers (Ln=La, Dy, Tb, Gd), where the Dy derivative shows slow magnetization relaxation. The strategy presented herein could be extended to access a broader library of hydrolyzed platforms (Hx LHPO ; x=1-8) that may represent mimics of nuclease enzymes.

Turn-off luminescence sensing, white light emission and magnetic studies of two-dimensional lanthanide MOFs.

The lanthanide metal organic framework compounds [Ln(BPTA)1.5(Bpy)]·0.5DMF (Ln = Y, Eu, Gd, Tb, Dy; 1a-5a) and [Ln(BPTA)1.5(Phen)]·0.5DMF (Ln = Y, Eu, Gd, Tb, Dy; 1b-5b) were prepared by employing 2,5-bis(prop-2-yn-1-yloxy)terephthalic acid (2,5-BPTA) as the primary ligand and 2,2'-bipyridine (1a-5a) and 1,10-phenanthroline (1b-5b) as the secondary ligands. Single-crystal structural studies on [Gd(BPTA)1.5(Bpy)]·0.5DMF (3a) and [Dy(BPTA)1.5(Phen)]·0.5DMF (5b) indicated that the compounds have a two-dimensional structure. The Y compound exhibits blue emission, and the other compounds exhibit emission in the expected regions (λex = 350 nm). White light emission was achieved by careful mixing of the red (Eu3+) and green (Tb3+) components in the blue emitting Y compound. Thus, Y0.96Tb0.02Eu0.02 (bpy) and Y0.939Tb0.06Eu0.001 (phen) were found to show white emission when excited using a wavelength of 350 nm. The introduction of N-N-containing ancillary ligands (i.e., bpy and phen) increased the overall quantum yield (QY) of white light emission to 31% and 43%, respectively. The high QY observed for the Tb and Eu compounds was found to be sensitive and selective for the fluorometric detection of azinphos-methyl pesticide and trinitrophenol (TNP) in an aqueous medium at the ppb level. The same behaviour was observed when utilising the compounds as onsite paper strip sensors. Their magnetic properties were also studied, revealing for the Tb and Dy derivatives slow relaxation of the magnetisation at low temperature. The present study highlights the usefulness of rigid π-conjugated molecules such as 2,2'-bipyridine and 1,10-phenanthroline in enhancing the many utilities of rare-earth-containing MOFs towards white light emission, the sensing of harmful and dangerous substances and magnetic properties.

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

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

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

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

Structural and magnetic characterization of tetranuclear [Ni(II)2Ln(III)2] complexes bearing tetra-branched Schiff base ligands

A series of tetranuclear [Ni(II)2Ln(III)2] complexes of general formula [Ni2Ln2(L)(H2O)9(OH)4Cl]∙3H2O∙Cl (1, 2, 5) (Ln = Dy (1), Tb (2), Ho (5)) and [Ni2Ln2(L)(H2O)12Cl] ∙3H2O∙5Cl (3, 4, 6, 7) (Ln = Gd (3), Sm (4), Nd (6), Pr (7)); H4L = N,N’,N’’,N’’’-tetra(3-methoxysalicylidene)-pentaerythritol) have been synthesized. The molecular structures and magnetic properties of 1–7 are reported. Structural analysis indicated that this family of clusters consists of a tetranuclear [Ni(II)2Ln(III)2] core, supported by a tetrapodal Schiff base ligand. Both Ni(II) ions adopt a distorted octahedral coordination environment, whilst the two terminal Ln(III) ions exhibit distorted tricapped trigonal prismatic geometries and are coordinated by eight or nine oxygen donor atoms. Magnetic measurements revealed that the Dy derivative of complex 1 displays typical d single-molecule magnet behaviour with the presence of slow magnetic relaxation. By contrast, complexes 2–7, no obvious SMM behaviour was exhibited, however for the Gd derivative 3, a significant magnetocaloric effect was observed.

Large magnetocaloric effect in EuGd2O4 and EuDy2O4

Magnetization, heat capacity and direct measurements of the magnetocaloric effect show that EuGd2O4 and EuDy2O4 have a remarkably large magnetocaloric effect at cryogenic temperatures, owing to their high magnetic density and low ordering temperatures. The Gd derivative orders antiferromagnetically at TN = 4.6 K, while its magnetocaloric effect largely exceeds that of the reference refrigerant Gadolinium Gallium Garnet (GGG) above 5 K. The Dy derivative undergoes two phase transitions at TC1 = 3.65 K and TC2 = 4.7 K, respectively, which are the result of a peculiar magnetic arrangement: the first Dy sublattice is parallel to the crystallographic c-axis, while the Eu sublattice makes a variable angle from 0o to 45o with the direction of the second Dy sublattice that lies in the ab-plane. EuDy2O4 has a lower magnetocaloric effect than EuGd2O4, yet larger than GGG. Both ordering mechanisms are semi-quantitatively explained within the frame of a mean-field simulation, which takes into account the magnetic anisotropy strength of the participating magnetic ions.

Trinuclear Lanthanide Coordination Clusters: Single-Molecule-Magnet Behavior and Catalytic Activity in the Friedel-Crafts Alkylation Reaction.

A new multidentate ligand (H3 L) was synthesized by the condensation reaction of 4-tert-butyl-2,6-diformylphenol and 2-amino-4-nitrophenol. The reaction of the ligand with hydrated lanthanide nitrate produced two isostructural trinuclear coordination clusters: [DyLn3 L3 (DMF)3 (H2 O)2 ] ⋅ 3.8DMFLn=Dy (1) and Nd (2) (DMF=N, N-dimethylformamide). Single-crystal X-ray diffraction analysis revealed that there are three lanthanide ions arranged in an almost perfect linear fashion in both complexes. Magnetic studies show single-molecule-magnet (SMM) behavior in the Dy derivative with τ0 =1.7×10-6 s and a thermal energy barrier of 7.0 cm-1 . Both complexes were used as catalysts towards the Friedel-Crafts alkylation reaction of indole with different aldehydes with yields varying from 59-98 %. Complex 1 showed better catalytic efficiency than complex 2. This is the first report of using trinuclear lanthanide coordination clusters as catalysts for the Friedel-Crafts alkylation reaction.

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.

Nanosized Chiral [Mn6Ln2] Clusters Modeled by Enantiomeric Schiff Base Derivatives: Synthesis, Crystal Structures, and Magnetic Properties

Two enantiomeric pairs of new 3d-4f heterometallic clusters have been built from two enantiomer Schiff base derivatives, labeled as R-/ S-H2L, in situ obtained from the condensation reactions with o-vanillin and R-/ S-2-phenylglycinol. The formulas of the series clusters are [Mn6Ln2(μ3-OH)4(μ4-O)(Ac)4(H2O)2( R-L)6]·NO3·OH (Ln = Dy (1R), Gd (2R)), [Mn6Ln2(μ3-OH)4(μ4-O)(Ac)4(H2O)2( S-L)6]·NO3·OH (Ln = Dy (1S), Gd (2S)), whose crystal structures and magnetic properties have been characterized. Structural analysis indicated that the above clusters consisted of a [Mn6Ln2] core, featuring a sandwich configuration. The results of magnetic measurements showed the presence of slow magnetic relaxation with the effective energy barrier of 14.85 K in two Dy derivatives under the condition of zero-dc field, while the significant magnetocaloric effect of Gd analogues was found in a wide temperature range.

Self-assembly of rare octanuclear quad(double-stranded) cluster helicates showing slow magnetic relaxation and the magnetocaloric effect

Four rare structurally novel octanuclear quad(double-strands) cluster helicates containing Ln8 polyhedron cores have been synthesized. Magnetic studies show that the Gd derivative exhibits the magnetocaloric effect and the Dy derivative shows slow magnetic relaxation under zero dc field.

Magnetic relaxation in [Ln(hfac)4]- anions with [Cu(hfac)-radical]nn+ cation chains as counterions.

Using a new nitronyl nitroxide radical Nit-Ph-PyIm, two novel 3d-4f complexes with the formula {[Ln(hfac)4]-[Cu(hfac)(Nit-Ph-PyIm)]+}n (LnIII = Gd 1, Dy 2) have been isolated (Nit-Ph-PyIm = 2-[4-[2-(2-pyridinyl)-1H-imidazol-1-yl]-phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; hfac = hexafluoroacetylacetonate). Interestingly, for both compounds, there are discrete [Ln(hfac)4]- anions while [Cu(hfac)-radical]nn+ chains serve as counter-ions in which the Nit-Ph-PyIm radicals link [Cu(hfac)]+ units through their NO groups and imidazolyl pyridine moieties. The [Cu(hfac)(Nit-Ph-PyIm)]+ unit is diamagnetic owing to the strong antiferromagnetic coupling between the Cu(ii) ion and the equatorially coordinated NO group. Complex 2 shows field-induced slow magnetization relaxation, arising from [Dy(hfac)4]- anions that exhibit distorted square-antiprism (D4d) geometries.

Slow Magnetic Relaxation in Ladder-Type and Single-Strand 2p-3d-4f Heterotrispin Chains.

Ladder-type and chain 2p-3d-4f complexes based on a bridging nitronyl nitroxide radical, namely, [LnCu(hfac)5(NIT-Ph-p-OCH2trz)]·0.5C6H14 [Ln = Y (1a), Dy (1b)] and [LnCu(hfac)5(NIT-Ph-p-OCH2trz)] [Ln = Y (2a), Dy (2b); NIT-Ph-p-OCH2trz = 2-[4-[(1H-1,2,4-triazol-1-yl)methoxy]phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; hfac = hexafluoroacetylacetonate) have been successfully achieved through a one-pot reaction of the NIT-Ph-p-OCH2trz radical with Cu(hfac)2 and Ln(hfac)3·2H2O. Complexes 1a and 1b feature a ladder-like structure, where the rails are made of Ln(III) and Cu(II) ions alternatively bridged by nitronyl nitroxide and the triazole units while the NIT-Ph-p-OCH2trz moieties act as the rungs of the ladder. Complexes 2a and 2b consist of one-dimensional nitronyl nitroxide bridged Ln coordination polymers with dangly Cu(II) units connected to the triazole moieties. All of compounds exhibit ferromagnetic NIT-Dy and/or NIT-Cu interactions. Both Dy derivatives (1b and 2b) show frequency-dependent out-of-phase magnetic susceptibility signals in a zero field indicating slow magnetic relaxation behavior.

Synthesis, luminescent and magnetic properties of new tetranuclear lanthanide complexes with 4-hydroxy-2,1,3-benzothiadiazolate and dibenzoylmethanide ligands

Four new tetranuclear complexes, [Ln4(dbm)4(O-btd)6(OH)2] 1a (Ln=Yb), 1b (Ln=Dy) and [Ln4(dbm)6(O-btd)4(OH)2] 2a (Ln=Yb), 2b (Ln=Dy) (O-btd=4-hydroxo-2,1,3-benzothiadiazolate and dbm=dibenzoylmethanide), and their solvates with toluene and tetrahydrofuran were synthesized. The magnetic properties of the complexes 1a, 1b, 2a and 2b have been studied, revealing different magnetic susceptibility patterns for the Yb(III) and Dy(III) complexes in the temperature range 80–300K. Upon lowering the temperature, a weak antiferromagnetic ordering is observed for both Yb compounds, while the Dy derivatives are assumed to show weak ferromagnetic interactions. The Yb complexes 1a and 2a demonstrate strong NIR luminescence at ∼1000nm in CH2Cl2 solution upon excitation of the (O-btd)− ligand. This observation suggests the (O-btd)− ligand to be an efficient antenna ligand for lanthanide-based NIR luminescence.

Crystal structures and magnetic properties of two series of phenoxo-O bridged dinuclear Ln2 (Ln = Gd, Tb, Dy) complexes.

Six dinuclear lanthanide compounds of the formulae [Ln2(3m-L4)2(L2)2(MeOH)2]·6MeOH (Ln = Gd - 1a, Tb - 1b, and Dy - 1c) and [Ln2(3m-L4)2(L2)2(DMF)2] (Ln = Gd - 2a, Tb - 2b, and Dy - 2c; DMF = N,N-dimethylformamide, H23m-L4 = (2-[(E)-(3-metoxysalicylidene)amino]phenol), and HL2 = 1,3-diphenyl-1,3-diketopropane) were prepared and characterized by elemental analysis, FTIR spectroscopy, thermogravimetric measurements, single-crystal X-ray structural analysis, and magnetometry, and Gd2 and Dy2 compounds by ab initio methods as well. The structural analysis revealed the isostructurallity of the compounds within the series of 1a-c and 2a-c. The analysis of the variable temperature magnetic data showed the presence of a weak antiferromagnetic coupling in the Gd2 compounds (J/cm-1 = -0.13 for 1a and J/cm-1 = -0.17 for 2a). The magnetocaloric effect was studied on compound 2a with the maximum value of -ΔSM = 22.9 J kg-1 K-1 at T = 2.0 K and B = 9 T, which is the highest value among the Gd2 double phenoxo-bridged compounds observed up to now. Both the Dy2 compounds (1c and 2c) exhibit slow-relaxation of magnetization in zero external static magnetic field. Magnetic anisotropy, intradimer magnetic coupling and magnetization blocking barriers were also studied by ab initio methods for 1c and 2c.

Lanthanide coordination complexes framed by sodium ions: slow relaxation of the magnetization in the Dy(III) derivative.

Using a new polydentate Schiff-base ligand (H3L) we isolated three new tetranuclear isostructural lanthanide complexes with the general formula [LnNa2(L)4(DMF)4(H2O)2(AcO)2]·4DMF·2H2O [Ln = Dy (1), Ho (2), or Er (3)]. The structural characterization of the complexes reveals that the Na+ ions are coordinated in the structure which gives them a structure-directing role in the molecule. The magnetic behavior of the systems was investigated by means of SQUID magnetometry which revealed that complex 1 exhibits single molecule magnet behavior at low temperatures which is enhanced by the application of a 2000 Oe static magnetic field. We were able to extract an effective barrier of Ueff = 43(1) K, however, we show that the consideration of an Orbach relaxation mechanism being the dominant is not always correct for lanthanides. On the contrary, we elaborate how in this system the relaxation is caused by a combination of a direct and a Raman process.

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.

Synthesis, structures and magnetism of heterotrimetallic Ni–Cu–Ln complexes based on a dicompartmental imine–oxime ligand

Four NiII–CuII–LnIII heterotrimetallic complexes have been prepared and structurally characterized. The Dy derivative behaves as a SMM with a small effective energy of 0.78 K under zero dc-applied field.