Family of double-cubane Mn4Ln2 (Ln = Gd, Tb, Dy, Ho) and Mn4Y2 complexes: a new Mn4Tb2 single-molecule magnet

The synthesis and characterization of a family of Mn(2)(III)Mn(2)(II)Ln(III)(2) complexes (Ln = Gd (1), Tb (2), Dy (3), and Ho (4)) of formula [Mn(4)Ln(2)O(2)(O(2)CBu(t))(6)(edteH(2))(2)(NO(3))(2)] are reported, where edteH(4) is N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine. The analogous Mn(4)Y(2) (5) complex has also been prepared. They were obtained from reaction of Ln(NO(3))(3) or Y(NO(3))(3) with Mn(O(2)CBu(t))(2), edteH(4), and NEt(3) in a 2:3:1:2 molar ratio. The crystal structures of representative 1 and 2 were obtained, and their core consists of a face-fused double-cubane [Mn(4)Ln(2)(μ(4)-O(2-))(2)(μ(3)-OR)(4)] unit. Such double-cubane units are extremely rare in 3d metal chemistry and unprecedented in 3d-4f chemistry. Variable-temperature, solid-state dc and ac magnetic susceptibility studies on 1-5 were carried out. Fitting of dc χ(M)T vs T data for 5 gave J(bb) (Mn(III)···Mn(III)) = -32.6(9) cm(-1), J(wb) (Mn(II)···Mn(III)) = +0.5(2) cm(-1), and g = 1.96(1), indicating a |n, 0, n> (n = 0-5) 6-fold-degenerate ground state. The data for 1 indicate an S = 12 ground state, confirmed by fitting of magnetization data, which gave S = 12, D = 0.00(1) cm(-1), and g = 1.93(1) (D is the axial zero-field splitting parameter). This ground state identifies the Mn(II)···Gd(III) interactions to be ferromagnetic. The ac susceptibility data independently confirmed the conclusions about 1 and 5 and revealed that 2 displays slow relaxation of the magnetization vector for the Mn(4)Tb(2) analogue 2. The latter was confirmed as a single-molecule magnet by observation of hysteresis below 0.9 K in magnetization vs dc field scans on a single crystal of 2·MeCN on a micro-SQUID apparatus. The hysteresis loops also displayed well-resolved quantum tunneling of magnetization steps, only the second 3d-4f SMM to do so.     

Heterometallic 20-membered {Fe16Ln4} (Ln = Sm, Eu, Gd, Tb, Dy, Ho) metallo-ring aggregates

The reaction of triethanolamine (teaH(3)) with [Fe(III)(3)O(O(2)CCH(3))(6)(H(2)O)(3)]Cl·6H(2)O and Ln(NO(3))(3)·6H(2)O in acetonitrile yields [Fe(16)Ln(4)(tea)(8)(teaH)(12)(μ-O(2)CCH(3))(8)](NO(3))(4)·16H(2)O·xMeCN (Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5), Ho (6); x = 10 or 11). These 20-membered metallo-ring complexes are the largest such single-stranded oxygen-bridged rings so far reported. The structure is stabilised by two of the acetate ligands, which form anti,anti-bridges across the centre of the ring, pinching the ring and giving it rigidity. The magnetic properties are dominated by the antiferromagnetic couplings between the Fe(III) centres. Although the Fe(2) and Fe(6) sub-chains within the ring are fully spin-compensated at low temperatures with S(subchain) = 0, coupling between the Gd(III) cations and the Fe(III) centres at the ends of the sub-chains (in 3) results in a pinning of the lanthanide spins. The (57)Fe M?ssbauer spectra of 3 and 5 obtained at low temperatures are consistent with the presence of Fe(III) intracluster strong antiferromagnetic coupling. The applied field spectrum for 3 reveals no magnetic hyperfine interaction apart from that of the nucleus with the applied field, while the one for 5 is a superposition of three subspectra which show contributions from each of the peripheral as well as from the central iron sites.     

Fluoroplatinate(IV) der Lanthaniden LnF[PtF6]. (Ln = Pr,Sm, Gd,Tb, Dy,Ho, Er)

Fluoroplatinates(IV) of the Lanthanides LnF[PtF₆] (Ln = Pr, Sm, Gd, Tb, Dy, Ho, Er) For the first time fluorides LnF[PtF₆] (Ln = Pr, Sm, Gd, Tb, Dy, Ho, Er), all yellow have been obtained. From single crystal data they crystallize monoclinic, space group P2₁/n?C (No. 14), Z = 4, Pr: a = 1 125.77(19) pm, b = 559.04(7) pm, c = 910.27(17) pm, β = 107.29(1)°; Sm: a = 1 114.63(31) pm, b = 552.70(12) pm, c = 898.02(20) pm, β = 107.24(2)°; Gd: a = 1 112.12(15) pm, b = 551.22(7) pm, c = 891.99(11) pm, β = 107.09(1)°; Tb (Powder data): a = 1 108.88(20) pm, b = 552.71(9) pm, c = 889.56(16) pm, β = 107.30(1)°; Dy: a = 1 100.28(23) pm, b = 547.77(8) pm, c = 882.41(13) pm, β = 107.32(1); Ho: a = 1 099.11(16) pm, b = 546.16(7) pm, c = 879.45(15) pm, β = 107.34(1)°; Er: a = 1 095.10(16) pm, b = 544.82(10) pm, c = 874.85(14) pm, β = 107.37(1)°.     

Luminescence of LnIII dithiocarbamate complexes (Ln = La, Pr, Sm, Eu, Gd, Tb, Dy)

We have discovered room temperature photoluminescence in Sm3+ and Pr3+ dithiocarbamate complexes. Surprisingly, these complexes exhibit more intense emission than those of the Eu3+, Tb3+, and Dy3+ analogues. The electronic absorption, excitation, and emission spectra are reported for the complexes [Ln(S2CNR2)3L] and NH2Et2[Ln(S2CNEt2)4], where Ln = Sm, Pr; R = ethyl, ibutyl, benzyl; and L = 1,10-phenanthroline, 2,2'-bipyridine, and 5-chloro-1,10-phenanthroline. The lowest ligand-localized triplet energy level (T1) of the complexes are determined from the phosphorescence spectra of analogous La3+ and Gd3+ chelates. The luminescence decay curves were measured to determine the excited-state lifetimes for the Pr3+ and Sm3+ complexes. X-ray crystal structures of Sm(S2CNiBu2)3phen, Pr(S2CNEt2)3phen, and Pr(S2CNiBu2)3phen are also reported.     

Defect-dicubane Ni2Ln2 (Ln = Dy, Tb) single molecule magnets

Two pairs of Ni(2)Dy(2) and Ni(2)Tb(2) complexes, [Ni(2)Ln(2)(L)(4)(NO(3))(2)(DMF)(2)] {Ln = Dy (1), Tb (2)} and [Ni(2)Ln(2)(L)(4)(NO(3))(2)(MeOH)(2)]·3MeOH {Ln = Dy (3), Tb (4)} (H(2)L is the Schiff base resulting from the condensation of o-vanillin and 2-aminophenol) possessing a defect-dicubane core topology were synthesized and characterized. All four complexes are ferromagnetically coupled, and the two Dy-analogues are found to be Single Molecule Magnets (SMMs) with energy barriers in the range 18-28 K. Compound 1 displays step-like hysteresis loops, confirming the SMM behavior. Although 1 and 3 show very similar structural topologies, the dynamic properties of 1 and 3 are different with blocking temperatures (3.2 and 4.2 K at a frequency of 1500 Hz) differing by 1 K. This appears to result from a change in orientation of the nitrate ligands on the Dy(III) ions, induced by changes in ligands on Ni(II).     

Synthesis, structure and magnetic properties of linear heterobimetallic trinuclear Mn2Ln (Ln = Eu, Gd, Dy) complexes

The reaction of (S)P[N(CH(3))N[double bond, length as m-dash]CH-C(6)H(3)-2-OH-3-OCH(3)](3) with a Mn(II) salt followed by a Ln(III) salt (Ln = Eu, Gd and Dy), afforded linear heterometallic complexes [L(2)Mn(2)Ln](+) that showed interesting magnetic properties.     

Ferromagnetic exchange couplings showing a chemical trend in Cu-Ln-Cu complexes (Ln = Gd, Tb, Dy, Ho, Er)

Exchange couplings in isomorphous [LnCu(2)] were evaluated by high-frequency electron paramagnetic resonance and magnetization studies. The exchange parameter J(Ln-Cu) was decreased with an increase in the atomic number; J(Ln-Cu)/k(B) = 4.45(11), 2.27(6), 0.902(10), 0.334(3), and 0.136(8) K for Ln = Gd, Tb, Dy, Ho, and Er, respectively.     

The thermodynamic properties of Ln2BaO4 (Ln = Sm, Dy, Ho)

The thermodynamic properties of the Ln₂BaO₄ phases (Ln = Dy, Ho, Sm) were studied by the electromotive force method with a fluoride electrolyte (890–1180 K), solution calorimetry in 1.07 N hydrochloric acid at 298.15 K, and differential scanning calorimetry (298–860 K). The experimental data were jointly processed, and the thermodynamic functions of the compounds over the temperature range 298–1200 K were calculated.     

Luminescence tuning of imidazole-based lanthanide(III) complexes [Ln = Sm, Eu, Gd, Tb, Dy

To tune the lanthanide luminescence in related molecular structures, we synthesized and characterized a series of lanthanide complexes with imidazole-based ligands: two tripodal ligands, tris{[2-{(1-methylimidazol-2-yl)methylidene}amino]ethyl}amine (Me(3)L), and tris{[2-{(imidazol-4-yl)methylidene}amino]ethyl}amine (H(3)L), and the dipodal ligand bis{[2-{(imidazol-4-yl)methylidene}amino]ethyl}amine (H(2)L). The general formulas are [Ln(Me(3)L)(H(2)O)(2)](NO(3))(3)·3H(2)O (Ln = 3+ lanthanide ion: Sm (1), Eu (2), Gd (3), Tb (4), and Dy (5)), [Ln(H(3)L)(NO(3))](NO(3))(2)·MeOH (Ln(3+) = Sm (6), Eu (7), Gd (8), Tb (9), and Dy (10)), and [Ln(H(2)L)(NO(3))(2)(MeOH)](NO(3))·MeOH (Ln(3+) = Sm (11), Eu (12), Gd (13), Tb (14), and Dy (15)). Each lanthanide ion is 9-coordinate in the complexes with the Me(3)L and H(3)L ligands and 10-coordinate in the complexes with the H(2)L ligand, in which counter anion and solvent molecules are also coordinated. The complexes show a screw arrangement of ligands around the lanthanide ions, and their enantiomorphs form racemate crystals. Luminescence studies have been carried out on the solid and solution-state samples. The triplet energy levels of Me(3)L, H(3)L, and H(2)L are 21?000, 22?700, and 23?000 cm(-1), respectively, which were determined from the phosphorescence spectra of their Gd(3+) complexes. The Me(3)L ligand is an effective sensitizer for Sm(3+) and Eu(3+) ions. Efficient luminescence of Sm(3+), Eu(3+), Tb(3+), and Dy(3+) ions was observed in complexes with the H(3)L and H(2)L ligands. Ligand modification by changing imidazole groups alters their triplet energy, and results in different sensitizing ability towards lanthanide ions.     

Structures of nonlinear hexagonal boratotungstates Ln3BWO9 (Ln = La, Pr, Nd, Sm, Gd, Tb, Dy)

Polycrystalline boratotungstates of composition Ln₃BWO₉ (Ln = Pr, Nd, Sm, Gd, Tb, Dy) are prepared by solid-phase synthesis and structurally studied. The structures are refined using the Rietveld method for hexagonal space group P6₃ (Z = 2). The boratotungstate structures are frameworks. The rare-earth cations in the structure are coordinated by an array of nine oxygen atoms (three oxygen atoms from borato groups BO₃ and six from WO₆ polyhedra). The nature of the optical nonlinearity in the hexagonal boratotungstates Ln₃BWO₉ is a direct consequence of the acentricity of both the tungstate and the rare-earth polyhedra in the structure. Dimorphism is discovered in polycrystalline La₃BWO₉.     

Unprecedented (Cu2Ln)n complexes (Ln = Gd3+, Tb3+): a new "single chain magnet"

The magnetic study of a trinuclear Cu-Gd-Cu complex confirms that such basic units self-assemble to yield a high spin species. A nice fit of the magnetic data is obtained for an infinite chain of tetranuclear Gd(2)Cu(2) motifs linked through the Gd ions located at the opposite vertexes of the tetranuclear motifs according to two Cu-Gd coordination modes, a double bridging through phenoxo and alkoxo oxygen atoms and a single bridging through deprotonated amide functions. The two interaction pathways are ferromagnetic. Alternating current susceptibility measurements confirm that the equivalent copper-terbium entity is a single chain magnet with a barrier height for reversal of the magnetization equal to 28.5 K.     

Synthesis and single-crystal x-ray diffraction examination of a structurally homologous series of tetracoordinate heteroleptic anionic lanthanide complexes: Ln[N[Si(CH3)2CH2CH2Si(CH3)2]]3(mu-Cl)Li(L)3 (Ln = Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb; (L)3 =(THF)3, (Et2O)3, (THF)2(Et2O)

Anhydrous lanthanide(III) chlorides (Ln = Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) react with 3 equiv of lithium 2,2,5,5-tetramethyl-2,5-disila-1-azacyclopentanide, Li[N[Si(CH3)2CH2Ch2Si(CH3)2]], in THF or Et(2)O to afford the monomeric four-coordinate heteroleptic ate complexes Ln[N[Si(CH3)2CH2CH2Si(CH3)2]]3(mu-Cl)Li(THF/Et2O)3 (Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5), Ho (6), Er (7), Tm (8), Yb (9)), whose solid-state structures were determined by the single-crystal X-ray diffraction technique. All complexes additionally were characterized by melting point determination, elemental analyses, and mass spectrometry.     

Thermochemistry of rare earth complexes [Ln(Ala)2(Im)(H2O)](ClO4)3 (Ln=Pr, Gd)

The two complexes, [Ln(Ala)₂(Im)(H₂O)](ClO₄)₃ (Ln=Pr, Gd), were synthesized and characterized. Using a solution-reaction isoperibol calorimeter, standard enthalpies of reaction of two reactions: LnCl₃⋅6H₂O(s)+2Ala(s)+Im(s)+3NaClO₄(s)=[Ln(Ala)₂(Im)(H₂O)](ClO₄)₃(s)+3NaCl(s)+5H₂O(l) (Ln=Pr, Gd), at T=298.15 K, were determined to be (39.26±0.10) and (5.33±0.12) kJ mol^–1 , respectively. Standard enthalpies of formation of the two complexes at T=298.15 K, Δ_fH^Θ_m {[Ln(Ala)₂(Im)(H₂O)](ClO₄)₃(s)} (Ln=Pr, Gd), were calculated as –(2424.2±3.3) and –(2443.4±3.3) kJ mol^–1 , respectively.     

Trends in trigonal prismatic Ln-[1]ferrocenophane complexes and discovery of a Ho3+ single-molecule magnet

Lanthanide metallocenophanes are an intriguing class of organometallic complexes that feature rare six-coordinate trigonal prismatic coordination environments of 4f elements with close intramolecular proximity to transition metal ions. Herein, we present a systematic study of the structural and magnetic properties of the ferrocenophanes, [LnFc₃(THF)₂Li₂]⁻, of the late trivalent lanthanide ions (Ln = Gd (1), Ho (2), Er (3), Tm (4), Yb (5), Lu (6)). One major structural trend within this class of complexes is the increasing diferrocenyl (Fc²⁻) average twist angle with decreasing ionic radius (r_ion) of the central Ln ion, resulting in the largest average Fc²⁻ twist angles for the Lu³⁺ compound 6. Such high sensitivity of the twist angle to changes in r_ion is unique to the here presented ferrocenophane complexes and likely due to the large trigonal plane separation enforced by the ligand (>3.2 Å). This geometry also allows the non-Kramers ion Ho³⁺ to exhibit slow magnetic relaxation in the absence of applied dc fields, rendering compound 2 a rare example of a Ho-based single-molecule magnet (SMM) with barriers to magnetization reversal (U) of 110–131 cm⁻¹. In contrast, compounds featuring Ln ions with prolate electron density (3–5) don''t show slow magnetization dynamics under the same conditions. The observed trends in magnetic properties of 2–5 are supported by state-of-the-art ab initio calculations. Finally, the magneto-structural relationship of the trigonal prismatic Ho-[1]ferrocenophane motif was further investigated by axial ligand (THF in 2) exchange to yield [HoFc₃(THF*)₂Li₂]⁻ (2-THF*) and [HoFc₃(py)₂Li₂]⁻ (2-py) motifs. We find that larger average Fc²⁻ twist angles (in 2-THF* and 2-py as compared to in 2) result in faster magnetic relaxation times at a given temperature.

Lanthanide ferrocenophanes are an intriguing class of organometallic complexes that feature rare six-coordinate trigonal prismatic coordination environments of 4f elements with close intramolecular proximity to iron ions.     

A family of 3d-4f octa-nuclear [Mn(III)(4)Ln(III)(4)] wheels (Ln = Sm, Gd, Tb, Dy, Ho, Er, and Y): synthesis, structure, and magnetism

We present the syntheses, crystal structures, and magnetochemical characterizations for a family of isostructural [Mn(4)Ln(4)] compounds (Ln = Sm, Gd, Tb, Dy, Ho, Er, and Y). They were prepared from the reactions of formic acid, propionic acid, N-n-butyl-diethanolamine, manganese perchlorate, and lanthanide nitrates under the addition of triethylamine in MeOH. The compounds possess an intriguing hetero-octanuclear wheel structure with four Mn(III) and four Ln(III) ions alternatively arranged in a saddle-like ring, where formate ions act as key carboxylate bridges. In the lattice, the molecules stack into columns in a quasi-hexagonal arrangement. Direct current (dc) magnetic susceptibility measurements indicated the depopulation of the Stark components at low temperature and/or very weak antiferromagnetic interactions between magnetic centers. The zero-field alternating current (ac) susceptibility studies revealed that the compounds containing Sm, Tb, and Dy showed frequency-dependent out-of-phase signals, indicating they are single-molecule magnets (SMMs). Magnetization versus applied dc field sweeps on a single crystal of the Dy compound down to 40 mK exhibited hysteresis depending on temperatures and field sweeping rates, further confirming that the Dy compound is a SMM. The magnetization dynamics of the Sm and Y compounds investigated under dc fields revealed that the relaxation of the Sm compound is considered to be dominated by the two-phonon (Orbach) process while the Y compound displays a multiple relaxation process.     

Linear trinuclear mixed-metal Co(II)-Gd(III)-Co(II) single-molecule magnet: [L(2)Co(2)Gd][NO(3)] x 2CHCl(3) (LH(3) = (S)P[N(Me)N=CH-C(6)H(3)-2-OH-3-OMe](3))

A linear trinuclear mixed-metal Co(2)Gd complex supported by two phosphorus-based multisite coordination ligands has been shown to be a single-molecule magnet.     

Family of carboxylate- and nitrate-diphenoxo triply bridged dinuclear Ni(II)Ln(III) complexes (Ln = Eu, Gd, Tb, Ho, Er, Y): synthesis, experimental and theoretical magneto-structural studies, and single-molecule magnet behavior

Seven acetate-diphenoxo triply bridged M(II)-Ln(III) complexes (M(II) = Ni(II) and Ln(III) = Gd, Tb, Ho, Er, and Y; M(II) = Zn(II) and Ln(III) = Ho(III) and Er(III)) of formula [M(μ-L)(μ-OAc)Ln(NO(3))(2)], one nitrate-diphenoxo triply bridged Ni(II)-Tb(III) complex, [Ni(μ-L)(μ-NO(3))Tb(NO(3))(2)]·2CH(3)OH, and two diphenoxo doubly bridged Ni(II)-Ln(III) complexes (Ln(III) = Eu, Gd) of formula [Ni(H(2)O)(μ-L)Ln(NO(3))(3)]·2CH(3)OH have been prepared in one pot reaction from the compartmental ligand N,N',N"-trimethyl-N,N"-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine (H(2)L). Moreover, Ni(II)-Ln(III) complexes bearing benzoate or 9-anthracenecarboxylate bridging groups of formula [Ni(μ-L)(μ-BzO)Dy(NO(3))(2)] and [Ni(μ-L)(μ-9-An)Dy(9-An)(NO(3))(2)]·3CH(3)CN have also been successfully synthesized. In acetate-diphenoxo triply bridged complexes, the acetate bridging group forces the structure to be folded with an average hinge angle in the M(μ-O(2))Ln bridging fragment of ~22°, whereas nitrate-diphenoxo doubly bridged complexes and diphenoxo-doubly bridged complexes exhibit more planar structures with hinge angles of ~13° and ~2°, respectively. All Ni(II)-Ln(III) complexes exhibit ferromagnetic interactions between Ni(II) and Ln(III) ions and, in the case of the Gd(III) complexes, the J(NiGd) coupling increases weakly but significantly with the planarity of the M-(O)(2)-Gd bridging fragment and with the increase of the Ni-O-Gd angle. Density functional theory (DFT) theoretical calculations on the Ni(II)Gd(III) complexes and model compounds support these magneto-structural correlations as well as the experimental J(NiGd) values, which were found to be ~1.38 and ~2.1 cm(-1) for the folded [Ni(μ-L)(μ-OAc)Gd(NO(3))(2)] and planar [Ni(H(2)O)(μ-L)Gd(NO(3))(3)]·2CH(3)OH complexes, respectively. The Ni(II)Dy(III) complexes exhibit slow relaxation of the magnetization with Δ/k(B) energy barriers under 1000 Oe applied magnetic fields of 9.2 and 10.1 K for [Ni(μ-L)(μ-BzO)Dy(NO(3))(2)] and [Ni(μ-L)(μ-9-An)Dy(9-An)(NO(3))(2)]·3CH(3)CN, respectively.     

Chemical trend of Ln-M exchange couplings in heterometallic complexes with Ln = Gd, Tb, Dy, Ho, Er and M = Cu, V

The 4f-3d exchange couplings were definitively and precisely determined in the dinuclear complexes (Ln-M) involving double μ-oxo-bridges, by means of combined high-frequency electron paramagnetic resonance and pulsed-field magnetization techniques, revealing a monotonic decrease of ferromagnetic J(Ln-Cu) in the order of the atomic number, (64)Gd to (68)Er.