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 Ln^III—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 Ln^III centers are bridged by two bidentate bridging (η¹:η¹:μ₂) and two chelating-bridging (η¹:η²:μ₂) acetate groups. The Ln^III 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 Ln^III 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 Tb^III 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 Gd^III…Gd^III exchange interactions in 3; the J value is −0.09(1) cm⁻¹ based on the spin Hamiltonian Ĥ = −J(Ŝ_Gd1·Ŝ_Gd2).     

Tuning the photophysical properties of lanthanide(iii)/zinc(ii) ‘encapsulated sandwich’ metallacrowns emitting in the near-infrared range

A family of Zn₁₆Ln(HA)₁₆ metallacrowns (MCs; Ln = Yb^III, Er^III, and Nd^III; HA = picoline- (picHA²⁻), pyrazine- (pyzHA²⁻), and quinaldine- (quinHA²⁻) hydroximates) with an ‘encapsulated sandwich’ structure possesses outstanding luminescence properties in the near-infrared (NIR) and suitability for cell imaging. Here, to decipher which parameters affect their functional and photophysical properties and how the nature of the hydroximate ligands can allow their fine tuning, we have completed this Zn₁₆Ln(HA)₁₆ family by synthesizing MCs with two new ligands, naphthyridine- (napHA²⁻) and quinoxaline- (quinoHA²⁻) hydroximates. Zn₁₆Ln(napHA)₁₆ and Zn₁₆Ln(quinoHA)₁₆ exhibit absorption bands extended into the visible range and efficiently sensitize the NIR emissions of Yb^III, Er^III, and Nd^III upon excitation up to 630 nm. The energies of the lowest singlet (S₁), triplet (T₁) and intra-ligand charge transfer (ILCT) states have been determined. Ln^III-centered total (Q^L_Ln) and intrinsic (Q^Ln_Ln) quantum yields, sensitization efficiencies (η_sens), observed (τ_obs) and radiative (τ_rad) luminescence lifetimes have been recorded and analyzed in the solid state and in CH₃OH and CD₃OD solutions for all Zn₁₆Ln(HA)₁₆. We found that, within the Zn₁₆Ln(HA)₁₆ family, τ_rad values are not constant for a particular Ln^III. The close in energy positions of T₁ and ILCT states in Zn₁₆Ln(picHA)₁₆ and Zn₁₆Ln(quinHA)₁₆ are preferred for the sensitization of Ln^III NIR emission and η_sens values reach 100% for Nd^III. Finally, the highest values of Q^L_Ln are observed for Zn₁₆Ln(quinHA)₁₆ in the solid state or in CD₃OD solutions. With these data at hand, we are now capable of creating MCs with desired properties suitable for NIR optical imaging.

We have created a family of ‘encapsulated sandwich’ Zn₁₆Ln(HA)₁₆ metallacrowns and by detailed quantitative analysis demonstrated how the nature of the hydroximate ligand impacts photophysical properties of these complexes.     

Actinide arene-metalates: ion pairing effects on the electronic structure of unsupported uranium–arenide sandwich complexes

Addition of [UI₂(THF)₃(μ-OMe)]₂·THF (2·THF) to THF solutions containing 6 equiv. of K[C₁₄H₁₀] generates the heteroleptic dimeric complexes [K(18-crown-6)(THF)₂]₂[U(η⁶-C₁₄H₁₀)(η⁴-C₁₄H₁₀)(μ-OMe)]₂·4THF (118C6·4THF) and {[K(THF)₃][U(η⁶-C₁₄H₁₀)(η⁴-C₁₄H₁₀)(μ-OMe)]}₂ (1THF) upon crystallization of the products in THF in the presence or absence of 18-crown-6, respectively. Both 118C6·4THF and 1THF are thermally stable in the solid-state at room temperature; however, after crystallization, they become insoluble in THF or DME solutions and instead gradually decompose upon standing. X-ray diffraction analysis reveals 118C6·4THF and 1THF to be structurally similar, possessing uranium centres sandwiched between bent anthracenide ligands of mixed tetrahapto and hexahapto ligation modes. Yet, the two complexes are distinguished by the close contact potassium-arenide ion pairing that is seen in 1THF but absent in 118C6·4THF, which is observed to have a significant effect on the electronic characteristics of the two complexes. Structural analysis, SQUID magnetometry data, XANES spectral characterization, and computational analyses are generally consistent with U(iv) formal assignments for the metal centres in both 118C6·4THF and 1THF, though noticeable differences are detected between the two species. For instance, the effective magnetic moment of 1THF (3.74 μ_B) is significantly lower than that of 118C6·4THF (4.40 μ_B) at 300 K. Furthermore, the XANES data shows the U L_III-edge absorption energy for 1THF to be 0.9 eV higher than that of 118C6·4THF, suggestive of more oxidized metal centres in the former. Of note, CASSCF calculations on the model complex {[U(η⁶-C₁₄H₁₀)(η⁴-C₁₄H₁₀)(μ-OMe)]₂}²⁻ (1*) shows highly polarized uranium–arenide interactions defined by π-type bonds where the metal contributions are primarily comprised by the 6d-orbitals (7.3 ± 0.6%) with minor participation from the 5f-orbitals (1.5 ± 0.5%). These unique complexes provide new insights into actinide–arenide bonding interactions and show the sensitivity of the electronic structures of the uranium atoms to coordination sphere effects.

Use of Chatt metal-arene protocols with uranium leads to the synthesis of the first well-characterized, unsupported actinide–arenide sandwich complexes. The electronic structures of the actinide centres show a key sensitivity to ion pairing effects.     

Effect of lanthanide contraction on the mixed polyamine systems Ln/Sb/Se/(en+dien) and Ln/Sb/Se/(en+trien): Syntheses and characterizations of lanthanide complexes with a tetraelenidoantimonate ligand

Mixed polyamine systems Ln/Sb/Se/(en+dien) and Ln/Sb/Se/(en+trien) (Ln=lanthanide, en=ethylenediamine, dien=diethylenetriamine, trien=triethylenetetramine) were investigated under solvothermal conditions, and novel mixed-coordinated lanthanide(III) complexes [Ln(en)₂(dien)(η²-SbSe₄)] (Ln=Ce(1a), Nd(1b)), [Ln(en)₂(dien)(SbSe₄)] (Ln=Sm(2a), Gd(2b), Dy(2c)), [Ln(en)(trien)(μ-η¹,η²-SbSe₄)]_∞ (Ln=Ce(3a), Nd(3b)) and [Sm(en)(trien)(η²-SbSe₄)] (4a) were prepared. Two structural types of lanthanide selenidoantimonates were obtained across the lanthanide series in both en+dien and en+trien systems. The tetrahedral anion [SbSe₄]³⁻ acts as a monodentate ligand mono-SbSe₄, a bidentate chelating ligand η²-SbSe₄ or a tridentate bridging ligand μ-η¹,η²-SbSe₄ to the lanthanide(III) center depending on the Ln³⁺ ions and the mixed ethylene polyamines, indicating the effect of lanthanide contraction on the structures of the lanthanide(III) selenidoantimonates. The lanthanide selenidoantimonates exhibit semiconducting properties with E_g between 2.08 and 2.51 eV.     

Osmium(ii) tethered half-sandwich complexes: pH-dependent aqueous speciation and transfer hydrogenation in cells

Aquation is often acknowledged as a necessary step for metallodrug activity inside the cell. Hemilabile ligands can be used for reversible metallodrug activation. We report a new family of osmium(ii) arene complexes of formula [Os(η⁶-C₆H₅(CH₂)₃OH)(XY)Cl]^+/0 (1–13) bearing the hemilabile η⁶-bound arene 3-phenylpropanol, where XY is a neutral N,N or an anionic N,O⁻ bidentate chelating ligand. Os–Cl bond cleavage in water leads to the formation of the hydroxido/aqua adduct, Os–OH(H). In spite of being considered inert, the hydroxido adduct unexpectedly triggers rapid tether ring formation by attachment of the pendant alcohol–oxygen to the osmium centre, resulting in the alkoxy tethered complex [Os(η⁶-arene-O-κ¹)(XY)]ⁿ⁺. Complexes 1C–13C of formula [Os(η⁶:κ¹-C₆H₅(CH₂)₃OH/O)(XY)]⁺ are fully characterised, including the X-ray structure of cation 3C. Tether-ring formation is reversible and pH dependent. Osmium complexes bearing picolinate N,O-chelates (9–12) catalyse the hydrogenation of pyruvate to lactate. Intracellular lactate production upon co-incubation of complex 11 (XY = 4-Me-picolinate) with formate has been quantified inside MDA-MB-231 and MCF7 breast cancer cells. The tether Os–arene complexes presented here can be exploited for the intracellular conversion of metabolites that are essential in the intricate metabolism of the cancer cell.

New Os(ii) half-sandwich complexes bearing a pendant alcohol prompt reversible tether-ring formation upon aquation, protecting Os against deactivation. Excitingly, these complexes mediate hydrogenation of pyruvate to lactate inside cancer cells.     

An electrically conductive metallocycle: densely packed molecular hexagons with π-stacked radicals

Electrical conduction among metallocycles has been unexplored because of the difficulty in creating electronic transport pathways. In this work, we present an electrocrystallization strategy for synthesizing an intrinsically electron-conductive metallocycle, [Ni₆(NDI-Hpz)₆(dma)₁₂(NO₃)₆]·5DMA·nH₂O (PMC-hexagon) (NDI-Hpz = N,N′-di(1H-pyrazol-4-yl)-1,4,5,8-naphthalenetetracarboxdiimide). The hexagonal metallocycle units are assembled into a densely packed ABCABC… sequence (like the fcc geometry) to construct one-dimensional (1D) helical π-stacked columns and 1D pore channels, which were maintained under the liberation of H₂O molecules. The NDI cores were partially reduced to form radicals as charge carriers, resulting in a room-temperature conductivity of (1.2–2.1) × 10⁻⁴ S cm⁻¹ (pressed pellet), which is superior to that of most NDI-based conductors including metal–organic frameworks and organic crystals. These findings open up the use of metallocycles as building blocks for fabricating conductive porous molecular materials.

Intrinsically electron-conductive metallocycle was synthesized. π-Radicals play a key role in constructing π-stacked columns among molecular hexagons and achieving high electrical conductivity over 10⁻⁴ S cm⁻¹ in polycrystalline pellet.     

Structural diversity of mixed polypnictogen complexes: dicationic E2E′2 (E ≠ E′ = P,As, Sb,Bi) chains,cycles and cages stabilized by transition metals

The reactivity of the tetrahedral dipnictogen complexes [{CpMo(CO)₂}₂(μ,η²:η²-EE′)] (E, E′ = P, As, Sb, Bi; “Mo₂EE′”) towards different one-electron oxidation agents is reported. Oxidation with [Thia][TEF] (Thia⁺ = C₁₂H₈S₂⁺; TEF⁻ = Al{OC(CF₃)₃}₄⁻) leads to the selective formation of the radical monocations [Mo₂EE′]˙⁺, which immediately dimerize to the unprecedented dicationic E₂E′₂ ligand complexes [{CpMo(CO)₂}₄(μ₄,η²:η²:η²:η²-E′EEE′)]²⁺via E–E bond formation. Single crystal X-ray diffraction revealed that, in the case of Mo₂PAs and Mo₂PSb, P–P bond formation occurs yielding zigzag E₂P₂ (E = As (1), Sb (2)) chains, whereas Mo₂SbBi forms a Sb₂Bi₂ (5) cage, Mo₂AsSb an unprecedented As₂Sb₂ unit representing an intermediate stage between a chain- and a cage-type structure, and Mo₂AsBi a novel planar As₂Bi₂ (4a) cycle. Therefore, 1–5 bear the first substituent-free, dicationic hetero-E₄ ligands, stabilized by transition metal fragments. Furthermore, in the case of Mo₂AsSb, the exchange of the counterion causes changes in the molecular structure yielding an unusual, cyclic As₂Sb₂ ligand. The experimental results are corroborated by DFT calculations.

Unique dicationic hetero-tetrapnictogen E₂E′₂ (E ≠ E′ = P, As, Sb, Bi) chains and cages are obtained via oxidation of the tetrahedranes [{CpMo(CO)₂}₂(μ,η²:η²-EE′)]. Exchange of the counterion causes an unusual cyclization of the As₂Sb₂ ligand.     

Complexes of Bifunctional DO3A-N-(α-amino)propinate Ligands with Mg(II), Ca(II), Cu(II), Zn(II), and Lanthanide(III) Ions: Thermodynamic Stability,Formation and Dissociation Kinetics,and Solution Dynamic NMR Studies

The thermodynamic, kinetic, and structural properties of Ln³⁺ complexes with the bifunctional DO3A-ACE⁴⁻ ligand and its amide derivative DO3A-BACE⁴⁻ (modelling the case where DO3A-ACE⁴⁻ ligand binds to vector molecules) have been studied in order to confirm the usefulness of the corresponding Gd³⁺ complexes as relaxation labels of targeted MRI contrast agents. The stability constants of the Mg²⁺ and Ca²⁺ complexes of DO3A-ACE⁴⁻ and DO3A-BACE⁴⁻ complexes are lower than for DOTA⁴⁻ and DO3A³⁻, while the Zn²⁺ and Cu²⁺ complexes have similar and higher stability than for DOTA⁴⁻ and DO3A³⁻ complexes. The stability constants of the Ln(DO3A-BACE)⁻ complexes increase from Ce³⁺ to Gd³⁺ but remain practically constant for the late Ln³⁺ ions (represented by Yb³⁺). The stability constants of the Ln(DO3A-ACE)⁴⁻ and Ln(DO3A-BACE)⁴⁻ complexes are several orders of magnitude lower than those of the corresponding DOTA⁴⁻ and DO3A³⁻ complexes. The formation rate of Eu(DO3A-ACE)⁻ is one order of magnitude slower than for Eu(DOTA)⁻, due to the presence of the protonated amine group, which destabilizes the protonated intermediate complex. This protonated group causes the Ln(DO3A-ACE)⁻ complexes to dissociate several orders of magnitude faster than Ln(DOTA)⁻ and its absence in the Ln(DO3A-BACE)⁻ complexes results in inertness similar to Ln(DOTA)⁻ (as judged by the rate constants of acid assisted dissociation). The ¹H NMR spectra of the diamagnetic Y(DO3A-ACE)⁻ and Y(DO3A-BACE)⁻ reflect the slow dynamics at low temperatures of the intramolecular isomerization process between the SA pair of enantiomers, R-Λ(λλλλ) and S-Δ(δδδδ). The conformation of the C_α-substituted pendant arm is different in the two complexes, where the bulky substituent is further away from the macrocyclic ring in Y(DO3A-BACE)⁻ than the amino group in Y(DO3A-ACE)⁻ to minimize steric hindrance. The temperature dependence of the spectra reflects slower ring motions than pendant arms rearrangements in both complexes. Although losing some thermodynamic stability relative to Gd(DOTA)⁻, Gd(DO3A-BACE)⁻ is still quite inert, indicating the usefulness of the bifunctional DO3A-ACE⁴⁻ in the design of GBCAs and Ln³⁺-based tags for protein structural NMR analysis.     

Optimization of crystal packing in semiconducting spin-crossover materials with fractionally charged TCNQδ− anions (0 < δ < 1)

Co-crystallization of the prominent Fe(ii) spin-crossover (SCO) cation, [Fe(3-bpp)₂]²⁺ (3-bpp = 2,6-bis(pyrazol-3-yl)pyridine), with a fractionally charged TCNQ^δ− radical anion has afforded a hybrid complex [Fe(3-bpp)₂](TCNQ)₃·5MeCN (1·5MeCN, where δ = −0.67). The partially desolvated material shows semiconducting behavior, with the room temperature conductivity σ_RT = 3.1 × 10⁻³ S cm⁻¹, and weak modulation of conducting properties in the region of the spin transition. The complete desolvation, however, results in the loss of hysteretic behavior and a very gradual SCO that spans the temperature range of 200 K. A related complex with integer-charged TCNQ⁻ anions, [Fe(3-bpp)₂](TCNQ)₂·3MeCN (2·3MeCN), readily loses the interstitial solvent to afford desolvated complex 2 that undergoes an abrupt and hysteretic spin transition centered at 106 K, with an 11 K thermal hysteresis. Complex 2 also exhibits a temperature-induced excited spin-state trapping (TIESST) effect, upon which a metastable high-spin state is trapped by flash-cooling from room temperature to 10 K. Heating above 85 K restores the ground-state low-spin configuration. An approach to improve the structural stability of such complexes is demonstrated by using a related ligand 2,6-bis(benzimidazol-2′-yl)pyridine (bzimpy) to obtain [Fe(bzimpy)₂](TCNQ)₆·2Me₂CO (4) and [Fe(bzimpy)₂](TCNQ)₅·5MeCN (5), both of which exist as LS complexes up to 400 K and exhibit semiconducting behavior, with σ_RT = 9.1 × 10⁻² S cm⁻¹ and 1.8 × 10⁻³ S cm⁻¹, respectively.

Co-crystallization of the cationic complex [Fe(3-bpp)2]²⁺ with fractionally charged TCNQ^δ− anions (0 < δ < 1) affords semiconducting spin-crossover (SCO) materials. The abruptness of SCO is strongly dependent on the interstitial solvent content.     

Lanthanide-nitrate interaction in anhydrous acetonitrile and coordination numbers of the lanthanide ions: FT‒IR study

The interaction between lanthanide ions Ln^III (Ln = La, Nd, Sm–Dy, Er, Yb) and nitrate ions is investigated by FT-IR spectroscopy in dilute anhydrous MeCN solution. The work is performed for ratios R = [NO]_t/[Ln^III]_t ranging from 0 to 8 and for solutions generally 0.05M in Ln^III, prepared from anhydrous lanthanide perchlorates Ln(ClO₄)₃. When nitrate is progressively added to the Ln(ClO₄)₃ solutions, the formation of [Ln(NO₃)_n]^(3?n)+ species is clearly evidenced by the FT-IR spectra. All the NO₃^? ions are coordinated and bidentate. A quantitative study was performed using the v₁ and v₆ vibrational modes for coordinated NO ions. The average coordination numbers estimated for Nd, Eu, Tb, and Er in solutions of trinitrates are 9.0, 9.1, 8.3 and 8.2, respectively (±0.3 unit). In presence of an excess NO, these numbers become 9.8, 10.2, 10.0, 9.8, 9.9, and 9.9 (±0.3 unit) for La, Nd, Eu, Tb, Er, and Yb, respectively. No hexanitrato species forms under the experimental conditions used (R up to 8). The structural aspect of the various nitrato species is also investigated. In the pentanitrato species, all the ligands appear to be equivalent, while large inequivalences are observed for Ln(NO₃)₃ solutions. Since for the latter most of the absorption bands assigned to nitrate vibrations contain several components, a curve-fitting procedure has been used for decomposing the v₂, v₄ and v₆ vibrations. There is a considerable difference between Ln^III ions, the nitrate inequivalences being larger in the middle of the series.     

Lanthanide-mediated tuning of electronic and magnetic properties in heterotrimetallic cyclooctatetraenyl multidecker self-assemblies

The synthesis of a novel family of homoleptic COT-based heterotrimetallic self-assemblies bearing the formula [LnKCa(COT)₃(THF)₃] (Ln(iii) = Gd, Tb, Dy, Ho, Er, Tm, and Yb) is reported followed by their X-ray crystallographic and magnetic characterization. All crystals conform to the monoclinic P2₁/c space group with a slight compression of the unit cell from 3396.4(2) ų to 3373.2(4) ų along the series. All complexes exhibit a triple-decker structure having the Ln(iii) and K(i) ions sandwiched by three COT²⁻ ligands with an end-bound {Ca²⁺(THF)₃} moiety to form a non-linear (153.5°) arrangement of three different metals. The COT²⁻ ligands act in a η⁸-mode with respect to all metal centers. A detailed structural comparison of this unique set of heterotrimetallic complexes has revealed consistent trends along the series. From Gd to Yb, the Ln to ring-centroid distance decreases from 1.961(3) Å to 1.827(2) Å. In contrast, the separation of K(i) and Ca(ii) ions from the COT-centroid (2.443(3) and 1.914(3) Å, respectively) is not affected by the change of Ln(iii) ions. The magnetic property investigation of the [LnKCa(COT)₃(THF)₃] series (Ln(iii) = Gd, Tb, Dy, Ho, Er, and Tm) reveals that the Dy, Er, and Tm complexes display slow relaxation of their magnetization, in other words, single-molecule magnet (SMM) properties. This behaviour is dominated by thermally activated (Orbach-like) and quantum tunneling processes for [DyKCa(COT)₃(THF)₃] in contrast to [ErKCa(COT)₃(THF)₃], in which the thermally activated and Raman processes appear to be relevant. Details of the electronic structures and magnetic properties of these complexes are further clarified with the help of DFT and ab initio theoretical calculations.

A new class of heterotrimetallic COT-based self-assemblies accommodates metals from groups I–III in three different oxidation states and enables tuning of electronic and magnetic properties.     

Substituted aromatic pentaphosphole ligands – a journey across the p-block

The functionalization of pentaphosphaferrocene [Cp*Fe(η⁵-P₅)] (1) with cationic group 13–17 electrophiles is shown to be a general synthetic strategy towards P–E bond formation of unprecedented diversity. The products of these reactions are dinuclear [{Cp*Fe}₂{μ,η^5:5-(P₅)₂EX₂}][TEF] (EX₂ = BBr₂ (2), GaI₂ (3), [TEF]⁻ = [Al{OC(CF₃)₃}₄]⁻) or mononuclear [Cp*Fe(η⁵-P₅E)][X] (E = CH₂Ph (4), CHPh₂ (5), SiHPh₂ (6), AsCy₂ (7), SePh (9), TeMes (10), Cl (11), Br (12), I (13)) complexes of hetero-bis-pentaphosphole ((cyclo-P₅)₂R) or hetero-pentaphosphole ligands (cyclo-P₅R), the aromatic all-phosphorus analogs of prototypical cyclopentadienes. Further, modifying the steric and electronic properties of the electrophile has a drastic impact on its reactivity and leads to the formation of [Cp*Fe(μ,η^5:2-P₅)SbICp′′′][TEF] (8) which possesses a triple-decker-like structure. X-ray crystallographic characterization reveals the slightly twisted conformation of the cyclo-P₅R ligands in these compounds and multinuclear NMR spectroscopy confirms their integrity in solution. DFT calculations shed light on the bonding situation of these compounds and confirm the aromatic character of the pentaphosphole ligands on a journey across the p-block.

The reactivity of cationic electrophiles towards pentaphosphaferrocene [Cp*Fe(ƞ⁵-P₅)] is explored. We report P–E bond formation for electrophiles across the p-block, producing coordination complexes with unprecedented hetero-bispentaphosphole and hetero-pentaphosphole ligands.     

In silico design to enhance the barrier height for magnetization reversal in Dy(iii) sandwich complexes by stitching them under the umbrella of corannulene

Lanthanide based single molecular magnets (SMMs), particularly dysprocenium based SIMs, are well known for their high energy barrier for spin reversal (U_eff) and blocking temperatures (T_B). Enhancing these two parameters and at the same time obtaining ambient stability is key to realising end-user applications such as compact storage or as qubits in quantum computing. In this work, by employing an array of theoretical tools (DFT, ab initio CASSCF and molecular dynamics), we have modelled six complexes [(η⁵-corannulene)Dy(Cp)] (1), [(η⁵-corannulene)Dy(C₆H₆)] (2), [(η⁶-corannulene)Dy(Cp)] (3), [(η⁶-corannulene)Dy(C₆H₆)] (4), [(exo-η⁵-corannulene)Dy(endo-η⁵-corannulene)] (5), and [(endo-η⁵-corannulene)Dy(endo-η⁵-corannulene)] (6) containing corannulene as a capping ligand to stabilise Dy(iii) half-sandwich complexes. Our calculations predict a strong axiality exerted by the Dy–C interactions in all complexes. Ab initio calculations predict a very large barrier height for all six molecules in the order 1 (919 cm⁻¹) ≈ 3 (913 cm⁻¹) > 2 (847 cm⁻¹) > 4 (608 cm⁻¹) ≈ 5 (603 cm⁻¹) ≈ 6 (599 cm⁻¹), suggesting larger barrier heights for Cp ring systems, followed by six-membered arene systems and then corannulene. DFT based molecular dynamics calculations were performed on complexes 3, 5 and 6. For complexes 3 and 5, the geometries that are dynamically accessible are far fewer. The range of U_eff computed for molecular dynamics snapshots is high, indicating a possibility of translating the large U_eff obtained into attractive blocking temperatures in these complexes, but the converse is found for 6. Furthermore, an in-depth C–H bond vibrational analysis performed on complex 3 suggests that the vibration responsible for reducing the blocking temperature in dysprocenium SIMs is absent here as the C–H bonds are stronger and corannulene steric strain prevents the C(Cp)–Dy–C(Cor) bending. As [(η⁶-corannulene)TM(X)]⁺ (TM = Ru, Zr, Os, Rh, Ir and X = C₅Me₅, C₆Me₆) are known, the predictions made here have a higher prospect of yielding stability under ambient conditions, a very large U_eff value and a high blocking temperature – a life-giving combination to new generation SMMs.

Bringing half-sandwich Dy(iii) SIMs under the umbrella of corannulene was found to offer stability, greater barrier height and may offer higher blocking temperatures.     

Paramagnetic properties and molecular structure of coordination saturated inclusive lanthanide complexes with 18-crown-6 using NMR

Earlier NMR spectra of lanthanide complexes [Ln(18-crown-6)(NO₃)₃] have been analyzed by us (Babailov in Inorg Chem 51(3):1427–1433, 2012), where Ln³⁺ = La³⁺ (I), Ce³⁺ (II), Pr³⁺ (III) and Nd³⁺ (IV). The NMR signal assignment and conformational molecular dynamic have been found by 1D NOE and relaxation spectroscopy as well as on 2D NOESY and EXSY experiments at 170 K. In the present paper the ¹H NMR method is used to study the features of paramagnetic properties of complexes I–IV and [Eu(18-crown-6)(NO₃)₃] (V) at ambient temperature. The investigation was carried out by special method based on analysis of Δδ/z> on k(Ln)/z> (where k(Ln) is Bleaney’s constant, Δδ is paramagnetic contribution to the lanthanide-induced shifts). The obtained results indicate that the structure of the complexes (in CDCl₃ and CD₂Cl₂) are very similar.     

Solvent- and metal-directed lanthanide-organic frameworks based on pamoic acid: observation of slow magnetization relaxation,magnetocaloric effect and luminescent sensing

Two types of lanthanide coordination polymers, namely, [Ln(PA)(NO_3)(DMA)_3]_n(Ln=Gd(1), Dy(2), Eu(3), Tb(4))(type I), and {[Ln_2(PA)_3(DMF)_4]·2DMF}(Ln=Eu(5), Tb(6))(type II)(PA=Pamoic acid, DMA=dimethylacetamide,DMF=N,N-dimethylformamide), have been synthesized by the reaction of Ln(NO_3)_3·6H_2O with pamoic acid through layer diffusion method. These complexes were characterized by single crystal X-ray diffraction, infrared spectroscopy(IR),thermogravimetric analysis(TGA), fluorescence and magnetic measurements. Solvents and lanthanide atoms in the reaction play an important role in controlling different structures. Type I demonstrated 1-D linear chain structure connected by Ln atoms and PA ligands. Type II exhibited non-interpenetrating 3-D 6-connected 4_36~(12) nets based on binuclear [Ln_2(CO_2)_6(DMF)_4] cores.Magnetic properties of complexes 1–4 were investigated in details. Complex 1 shows significant magnetocaloric effect with–ΔS_m=20.37 J kg~(–1) K~(–1) at 3.0 K and 7 T. Complex 2 exhibits slow relaxation of the magnetization. Complexes 3–6 exhibit both ligand- and metal-centered fluorescent properties. Complex 6 demonstrates fluorescent sensing of DMF and Cu~(2+) ion.     

Hydrothermal Syntheses,Crystal Structures,and Luminescent Properties of Three Organic‐Lanthanide Complexes with 3‐Hydroxycinnamic Acid

Three new homodinuclear lanthanide(III) complexes [Ln₂(L)₆(2,2′‐bipy)₂] [Ln = Tb^III ( 1 ), Sm^III ( 2 ), Eu^III ( 3 ); HL = 3‐hydroxycinnamic acid (3‐HCA); 2,2′‐bipy = 2,2′‐bipyridine] were synthesized and characterized by IR spectroscopy, elemental analyses, and X‐ray diffraction techniques. Complexes 1 – 3 crystallize in triclinic system, space group P$\bar{1}$ . In all complexes the lanthanide ions are nine‐coordinate by two nitrogen atoms from the 2,2′‐bipy ligand and seven oxygen atoms from one chelating L ligands and four bridging L ligands, forming distorted tricapped trigonal prismatic arrangements. The lanthanide(III) ions are intramolecularly bridged by eight carboxylate oxygen atoms forming dimeric complexes with Ln ··· Ln distances of 3.92747(15), 3.9664(6), and 3.9415(4) Å for complexes 1 – 3 , respectively. The luminescent properties in the solid state of HL ligand and Eu^III complex are also discussed.     

Tough Photoluminescent Hydrogels Doped with Lanthanide

Photoluminescent hydrogels have emerged as novel soft materials with potential applications in many fields. Although many photoluminescent hydrogels have been fabricated, their scope of usage has been severely limited by their poor mechanical performance. Here, a facile strategy is reported for preparing lanthanide (Ln)‐alginate/polyacrylamide (PAAm) hydrogels with both high toughness and photoluminescence, which has been achieved by doping Ln³⁺ ions (Ln = Eu, Tb, Eu/Tb) into alginate/PAAm hydrogel networks, where Ln³⁺ ions serve as both photoluminescent emitters and physical cross‐linkers. The resulting hydrogels exhibit versatile advantages including excellent mechanical properties (∼MPa strength, ≈20 tensile strains, ≈10⁴ kJ m⁻³ energy dissipation), good photoluminescent performance, tunable emission color, excellent processability, and cytocompatibility. The developed tough photoluminescent hydrogels hold great promises for expanding the usage scope of hydrogels.

     

Thermodynamic properties of dimeric molecules of lanthanum and lanthanide trichlorides Ln2Cl6(gas)

The partial pressures of dimeric molecules Ln₂Cl₆ in the saturated vapor over lanthanum and lanthanide trichlorides LnCl₃ (Ln = La, ..., Nd, Sm, Gd, ..., Lu) have been determined by high-temperature mass spectrometry. From these data, the enthalpies of the gas-phase reaction Ln₂Cl₆ = 2LnCl₃ and the enthalpies of sublimation of the compounds under consideration in the form of Ln₂Cl₆ dimers have been calculated by the third law. Analogous characteristics have also been calculated by the second and third laws from the available literature data on the partial pressures of Ln₂Cl₆ in the course of sublimation (evaporation) of LnCl₃. Taking into account typical tendencies in the standard thermodynamic characteristics of lanthanum and lanthanide compounds, a set of recommended D ₂₉₈ ⁰ (LnCl₃-LnCl₃) values has been determined. This set has been used for calculating the enthalpies of atomization Δ_at H ₂₉₈ ⁰ (Ln₂Cl₆), where Ln = La, ..., Lu.     

Study of the fluorite–pyrochlore–fluorite phase transitions in Ln<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript> (Ln=Lu,Yb, Tm)

The ordering processes in Ln₂Ti₂O₇ (Ln=Lu, Yb, Tm) are studied by X-ray diffraction, thermal analysis, infrared absorption (IR) spectroscopy, and electrical conductivity measurements. The coprecipitation method followed by freeze-drying was used for Ln₂Ti₂O₇ synthesis. The region of low-temperature fluorite phase existence is 600 °C<T<740 °C. The low-temperature fluorite–pyrochlore phase transition in Ln₂Ti₂O₇ takes place at ~740–800 °C. Ln₂Ti₂O₇ (Ln=Lu, Yb, Tm) have the structure of disordered pyrochlore with antisite Ln–Ti defects at 800 °C<T<1,100 °C.The high-temperature pyrochlore–fluorite transformation takes place in Tm₂Ti₂O₇, Yb₂Ti₂O₇, and Lu₂Ti₂O₇ in air at T>1,600 °C. The conductivity values are 5·10^–3 S/cm for Tm₂Ti₂O₇, 6·10^–3 S/cm for Yb₂Ti₂O₇, and 10^–2 S/cm for Lu₂Ti₂O₇ at 740 °C. This order–disorder transition leads to a 2 orders of magnitude conductivity growth and a 10–30 times permittivity increase in Ln₂Ti₂O₇ samples obtained at 1,700 °C.Presented at the OSSEP Workshop Ionic and Mixed Conductors: Methods and Processes, Aveiro, Portugal, 10–12 April 2003     

Organometallic motifs in the structures of solid state ternary carbides of the late transition metals

Solid state ternary transition metal carbides containing carbon, a middle to late transition metal (Re to Ni), and a highly electropositive multivalent metal such as lanthanide, yttrium, or thorium exhibit a number of structural motifs resembling those in metal carbonyls and other transition metal derivatives of strong -acceptor ligands. This paper presents models for the chemical bonding in the transition metal—carbon subnetworks of the ternary late transition metal carbides LnCoC (Ln=lanthanide), Ln₂ReC₂, Th₂NiC₂, Ln₂FeC₄, Ln₃MC₄ (M=Fe, Co, Ni, Ru, Rh, Os, Ir), Ln₄NiC₅, Ca₄Ni₃C₅, and Er₈Rh₅C₁₂. Carbide ligands present in such materials include terminal C^4– in Th₂NiC₂ and Y₂ReC₂, ₂-C^4– in YCoC or Y₂ReC₂ similar to the central allene carbon atom, 1,2-bridging C ₂ ^4– in Sc₃CoC₄ formally derived from ethylene, ₃-bridging C ₂ ^4– in LnMC₂ (M=Fe, Co, Ni, Ru) formally derived from ethylene, and 1,1-bridging C ₂ ^2– in Ln₂FeC₄ isoelectronic with ₂-CO group in metal carbonyls.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1358–1366, August, 1994.