Resolution of Seven-Coordinate Complexes

Two pairs of chiral YbIII enantiomers presenting distinct NIR luminescence and circularly polarized luminescence performances with giant differences in second-harmonic generation responses

By introducing enantiomerically pure mono-bidentate N-donor ligands (LR/LS) into Yb(btfa)3(H2O)2 and Yb(dbm)3(H2O), respectively, two pairs of chiral YbIII enantiomers, namely Yb(btfa)3LR/Yb(btfa)3LS (D-1/L-1) and [Yb(dbm)3LR]·[Yb(dbm)3(C2H5OH)]/[Yb(dbm)3LS]·[Yb(dbm)3(C2H5OH)] (D-2/L-2) were isolated, where btfa- = 3-benzoyl-1,1,1-trifluoroacetonate, dbm- = dibenzoylmethanate, and LR/LS = (-)/(+)-4,5-pinenepyridyl-2-pyrazine. D-1/L-1 possess mononuclear structures in which the YbIII ions are eight-coordinated, while D-2/L-2 show cocrystal structures containing Yb(dbm)3(LR/LS) and Yb(dbm)3(C2H5OH) moieties in which the two YbIII ions are eight and seven-coordinated, respectively. They not only feature different molecular structures but also present distinct linear and nonlinear optical performances. Chiral mononuclear D-1 has better near infrared photo-luminescence (NIR-PL) and circularly polarized luminescence (CPL) performances than chiral cocrystal D-2. More remarkably, D-1/L-1 show large second-harmonic generation (SHG) responses (up to 1.25/1.28 × KDP) 18/16 times those of D-2/L-2 (0.07/0.08 × KDP). In addition, D-2/L-2 represent the first examples of lanthanide cocrystal complexes with NIR-PL, NIR-CPL and SHG properties.

Molecular Dynamics Studies of the Ho(III) Aqua-tris(dibenzoylmethane) Complex: Role of Water Dynamics

The seven-coordinate Ho(III) aqua-tris(dibenzoylmethane)(DBM) complex, referred to as Ho-(DBM)₃·H₂O, was first reported in the late 1960s. It has a threefold symmetric structure, with Ho at the center of three dibenzoylmethane ligands and hydrogen-bonded water to ligands. It is considered that the hydrogen bonds between the water molecule and the ligands surrounding Ho play an important role in the formation of its symmetrical structure. In this work, we developed new force-field parameters for classical molecular dynamics (CMD) simulations to theoretically elucidate the structure and dynamics of Ho-(DBM)₃·H₂O. To develop the force field, structural optimization and molecular dynamics were performed on the basis of ab initio calculations using the plane-wave pseudopotential method. The force-field parameters for CMD were then optimized to reproduce the data obtained from ab initio calculations. Validation of the developed force field showed good agreement with the experimental crystalline structure and ab initio data. The vibrational properties of water in Ho-(DBM)₃·H₂O were investigated by comparison with bulk liquid water. The vibrational motion of water was found to have a characteristic mode originating from stationary rotational motion along the c-axis of Ho(III) aqua-tris(dibenzoylmethane). Contrary to expectations, the hydrogen-bond dynamics of water in Ho-(DBM)₃·H₂O were found to be almost equivalent to those of bulk liquid water except for librational motion. This development route for force-field parameters for CMD and the establishment of water dynamics can advance the understanding of water-coordinated metal complexes with high coordination numbers such as Ho-(DBM)₃·H₂O.

Two Chiral YbIII Enantiomeric Pairs with Distinct Enantiomerically Pure N-Donor Ligands Presenting Significant Differences in Photoluminescence, Circularly Polarized Luminescence, and Second-Harmonic Generation

Using enantiomerically pure bidentate and tridentate N-donor ligands (¹L_R/¹L_S and ²L_R/²L_S) to replace two coordinated H₂O molecules of Yb(tta)₃(H₂O)₂, respectively, two eight- and nine-coordinated Yb^III enantiomeric pairs, namely, Yb(tta)₃¹L_R/Yb(tta)₃¹L_S (Yb-R-1/Yb-S-1) and [Yb(tta)₃²L_R]·CH₃CN/[Yb(tta)₃²L_S]·CH₃CN (Yb-R-2/Yb-S-2), were isolated, in which Htta = 2-thenoyltrifluoroacetone, ¹L_R/¹L_S = (-)/(+)-4,5-pinene-2,2'-bipyridine, and ²L_R/²L_S = (-)/(+)-2,6-bis(4',5'-pinene-2'-pyridyl)pyridine. Interestingly, they not only present distinct degrees of chirality but also show large differences in near-infrared (NIR) photoluminescence (PL), circularly polarized luminescence (CPL), and second-harmonic generation (SHG). Eight-coordinated Yb-R-1 with an asymmetric bidentate ¹L_R ligand has a high NIR-PL quantum yield (1.26%) and a long decay lifetime (20 μs) at room temperature, being more than two times those (0.48%, 8 μs) of nine-coordinated Yb-R-2 with a C₂-symmetric tridentate ²L_R ligand. In addition, Yb-R-1 displays an efficient CPL with a luminescence dissymmetry factor g_lum = 0.077, being 4 × Yb-R-2 (0.018). In particular, Yb-R-1 presents a strong SHG response (0.8 × KDP), which is 8 × Yb-R-2 (0.1 × KDP). More remarkably, the precursor Yb(tta)₃(H₂O)₂ exhibits a strong third-harmonic generation (THG) response (41 × α-SiO₂), while the introduction of chiral N-donors results in the switching of THG to SHG. Our interesting findings provide new insights into both the functional regulation and switching in multifunctional lanthanide molecular materials.

Piano-stool ruthenium(II) complexes with maleimide and phosphine or phosphite ligands: synthesis and activity against normal and cancer cells

In these studies, we designed and investigated cyto- and genotoxic potential of five ruthenium cyclopentadienyl complexes bearing different phosphine and phosphite ligands. All of the complexes were characterized with spectroscopic analysis (NMR, FT-IR, ESI-MS, UV-vis, fluorescence and XRD (for two compounds)). For biological studies, we used three types of cells - normal peripheral blood mononuclear (PBM) cells, leukemic HL-60 cells and doxorubicin-resistance HL-60 cells (HL-60/DR). We compared the results obtained with those obtained for the complex with maleimide ligand CpRu(CO)₂(η¹-N-maleimidato) 1, which we had previously reported. We observed that the complexes CpRu(CO)(PPh₃)(η¹-N-maleimidato) 2a and CpRu(CO)(P(OEt)₃)(η¹-N-maleimidato) 3a were the most cytotoxic for HL-60 cells and non-cytotoxic for normal PBM cells. However, complex 1 was more cytotoxic for HL-60 cells than complexes 2a and 3a (IC₅₀ = 6.39 μM vs. IC₅₀ = 21.48 μM and IC₅₀ = 12.25 μM, respectively). The complex CpRu(CO)(P(OPh)₃)(η¹-N-maleimidato) 3b is the most cytotoxic for HL-60/DR cells (IC₅₀ = 104.35 μM). We found the genotoxic potential of complexes 2a and 3a only in HL-60 cells. These complexes also induced apoptosis in HL-60 cells. Docking studies showed that complexes 2a and CpRu(CO)(P(Fu)₃)(η¹-N-maleimidato) 2b have a small ability to degrade DNA, but they may cause a defect in DNA damage repair mechanisms leading to cell death. This hypothesis is corroborated with the results obtained in the plasmid relaxation assay in which ruthenium complexes bearing phosphine and phosphite ligands induce DNA breaks.

Conglomerate, Racemate, and Achiral Crystals of Polymetallic Europium(III) Compounds of Bis- or Tris-β-diketonate Ligands and Circularly Polarized Luminescence Study

This work reports (a) conglomerate and racemic crystal structures of [(Δ,Δ,Δ,Δ,Δ,Δ)- or/and (Λ,Λ,Λ,Λ,Λ,Λ)-Eu^III ₆(TTP)₈(OH₂)₆Na₄] _n coordination polymers, (b) racemic crystal structures of (Δ,Δ,Δ,Δ)-/(Λ,Λ,Λ,Λ)-Eu^III ₄(TTP)₄(bipy)₄(MEK)₂(OH₂)₂ tetrahedral clusters, and (c) the achiral crystal structure of the [Eu^III ₂(BTP)₄(OH₂)₂Na₂] _n coordination polymer (where BTP = dianionic bis-β-diketonate, TTP = trianionic tris-β-diketonate, and bipy = 2,2'-bipyridine). The screw coordination arrangement of the TTP ligand has led to the formation of homoconfigurational racemic Eu^III products. The conglomerate crystallization of [Eu^III ₆(TTP)₈(OH₂)₆Na₄] _n appears to be caused by the presence of the sodium, Na⁺ counterions, and interactions between oxygen atoms and the trifluoromethyl unit of the TTP ligand and Na⁺ ions. All the Eu^III compounds exhibit characteristic red luminescence (⁵D₀ → ⁷F_J, J = 0-4) in solution or in the solid crystalline state. Circularly polarized luminescence (CPL) was observed in the chiral Eu^III ₆(TTP)₈(OH₂)₆Na₄] _n species, displaying a |g _lum| value in the range of 0.15 to 0.68 at the ⁵D₀ → ⁷F₁ emission band. Subtle changes of the [Eu^III ₆(TTP)₈(OH₂)₆Na₄] _n structure which may be due to selection of twinned crystals or crystals that do not correspond to a perfect spontaneous resolution, are considered to be responsible for the variation in the observed CPL values.

Modulating Two Pairs of Chiral DyIII Enantiomers by Distinct β-Diketone Ligands to Show Giant Differences in Single-Ion Magnet Performance and Nonlinear Optical Response

Using Dy(dbm)₃(H₂O) and Dy(btfa)₃(H₂O)₂ to react with enantiopure N-donors, (-)/(+)-4,5-pinenepyridyl-2-pyrazine (L_R/L_S), respectively, two pairs of chiral Dy^III enantiomers, Dy(dbm)₃L_R/Dy(dbm)₃L_S (R-1-Dy/S-1-Dy) and Dy(btfa)₃L_R/Dy(btfa)₃L_S (R-2-Dy/S-2-Dy) were obtained, wherein one of the benzene rings of dbm^- (dibenzoylmethanate) in R-1-Dy/S-1-Dy is displaced by the -CF₃ group of btfa^- (4,4,4-trifluoro-1-phenyl-1,3-butanedionate) in R-2-Dy/S-2-Dy. Interestingly, this substitution results not only in giant differences in their single-ion magnetic (SIM) performances but also in their completely different nonlinear optical (NLO) responses. R-1-Dy presents a large effective energy barrier (U_eff = 265.47 K) under zero applied field, being more than 4 × R-2-Dy (61.40 K). The discrepancy on their magnetic performances has been further elucidated by ab initio calculations. Meanwhile, R-1-Dy/S-1-Dy display the strongest third-harmonic generation responses (35/33 × α-SiO₂) among the known lanthanide NLO-active coordination compounds (CCs). On the contrary, R-2-Dy/S-2-Dy exhibit moderate second-harmonic generation responses (0.65/0.70 × KDP). These results not only give the first example of the CCs with both SMM/SIM behavior and a THG response but also provide an efficient strategy for achieving the function regulation and switch in multifunctional CCs.

Magnetic Properties and Second Harmonic Generation of Noncentrosymmetric Cyanido-Bridged Ln(III)-W(V) Assemblies

One-dimensional zigzag cyanido-bridged coordination polymers have been prepared as a result of self-assembly of lanthanide(III) ions with octacyanidotungstate(V) anions in the presence of N,N-dimethylacetamide (dma). All compounds crystallized in noncentrosymmetric space group P2₁ with a molecular formula of [Ln^III(dma)₅][W^V(CN)₈] [Ln = Gd (1), Tb (2), Dy (3), Ho (4), Er (5), Tm (6), Yb (7), Lu (8), or Y (9)]. Magnetic studies revealed weak antiferromagnetic interactions through Ln^III-NC-W^V bridges and the formation of ferrimagnetically coupled chains at very low temperatures. Moreover, temperature dependencies of magnetic susceptibilities were fitted using the crystal field parameters for Ln(III) ions, determined by the ab initio calculations, yielding magnetic coupling constants in the range of -1 to -5 cm^-1. The wide optical transparency of 1-9 has been determined using solid state absorption spectroscopy. Samples exhibited second harmonic (SH) generation properties with SH susceptibilities ranging from 4.7 × 10^-12 to 9.4 × 10^-11 esu due to the presence of nonlinear optical susceptibility tensor elements (χ_ijk) χ_zxx, χ_zyy, χ_zzz, χ_zxy, χ_yyz, χ_yzx, χ_xyz, and χ_xzx, corresponding to space group P2₁. The determined values were also compared with the results of theoretical calculations and previous reports, indicating a potential relationship between the type of lanthanide ion and the SH intensity.

The crystal structure of aqua-tris (1,3-diphenylpropane-1,3-dionato-κ2 O,O′)-lanthanum(III), C45H35LaO7

C45H35LaO7, trigonal, R3 (no. 146), a = 22.3832(11) Å, c = 6.4522(3) Å, V = 2799.5(3) Å3, Z = 3, R gt (F) = 0.0192, wRref (F 2) = 0.0462, T = 200 K.

Dinuclear Lanthanide(III) Complexes Showing Single-Molecule Magnet Behaviour and Optical Properties

Three dinuclear lanthanide(iii) complexes with an acetate bridge, which are synthesised by a Salen-type Schiff base and β-diketonate ligands, i.e. [Ln2L2(TTA)4(OAc)2]·CH2Cl2 (Ln=Eu (1), Gd (2), Dy (3); TTA=thenoyltrifluoroacetonate, H2L=N,N′-ethylenebis(salicylideneimine), are investigated. We obtained the structures of complexes 1–3 by X-ray crystallography. Notably, in terms of the structure of these complexes, what is intriguing is that the acetate groups link two Lniii ions, whereas the cadmium ions do not coordinate. Lanthanide-based luminescence is exhibited by complex 1, which exists in both the solid state and a methanol solution. Through magnetic analysis, it is found that a field-induced single-molecule magnet behaviour is exhibited by complex 3, and the energy barrier is shown to be Ueff=45.97K.

Structure and Stereochemistry of Adducts of Tris(dipivaloylmethanato)europium(III), Eu(dpm)3, with Some Dipolar Aprotic Unidentate O-Donors

Single crystal X-ray structural characterisations are reported for adducts of the form [(L-O)Eu(O,O′-dpm)3] obtained by the crystallisation of tris(dipivaloylmethanato)europium(iii) (dpm=[HC(C(tBu).CO)2]−) from an array of dipolar aprotic oxygen-donor solvents L (L=N-methylpyrrolidinone (nmp), trimethylphosphate, (MeO)3PO, (tmp), hexamethylphosphoramide (hmpa), dimethylacetamide (dma), dimethyl sulfoxide (dmso), and the bidentate octamethylpyrophosphoramide (ompa). In all adducts, the resulting arrays contain seven-coordinate metal atoms, which adopt two different isomeric forms of the mono-capped trigonal prismatic stereochemistry, the L=dma and dmso adducts corresponding to one type, nmp and tmp the other. The adduct formed with ompa behaves as a pair of discrete metal environments bridged by the O-ompa-O′ ligand, thus; [(dpm-O,O′)3Eu(O-ompa-O′)Eu(O,O′-dpm)3], and is found in two forms, one in which both Eu environments is of the tmp type, the other of the dmso/dma type. In the hmpa adduct, the asymmetric unit of the structure is a disordered composite of both types. In none of the adducts is there any further solvation beyond coordination of a single L.

Strong intramolecular DyIII–DyIII magnetic couplings up to 15.00 cm−1 in phenoxyl-bridged dinuclear 4f complexes

Unexpectedly, intramoleular Dy^III–Dy^III magnetic couplings are up to 15.00 cm⁻¹ in the phenolate-bridged Dy₂ complexes. And single-molecule magnet behavior is exhibited with effective energy of 76.18 K under zero dc field.

A fresh look at the structural diversity of dibenzoylmethanide complexes of lanthanides

Synthetic methods for dibenzoylmethanide lanthanide complexes as well as heterolanthanide ones were systematized revealing several species.

White-light emission based on a single component Sm(iii) complex and enhanced optical properties by doping methods

Six lanthanide complexes with enhanced tunable photoluminescence were designed and synthesized using codoping methods and single component white-light emission was achieved.

N Donor substituted acetylacetones – versatile ditopic ligands

Acetylacetone (2,4-pentanedione) derivatives with N donor substituents represent ditopic ligands with coordination sites of distinctly different Pearson hardness. Deprotonation of the acetylacetone (Hacac) moiety leads to O,O′ chelating monoanionic (acac) ligands suitable for coordination to hard cations. The softer N donor site(s) preferably act as nucleophiles towards softer partners. When the organic molecules are employed as linkers and coordinate via either site, they are often selective and allow to synthesize well-ordered heterometallic solids. This review addresses the derivatives of 17 pentanediones with nitrile, pyridyl and pyrazolyl moieties as N donor substituents, with an emphasis on structurally characterized compounds. Depending on the N donor substituents and the cations, O,O′ or N coordination will dominate. The nitrile-substituted compounds essentially behave as acetylacetones; they may easily O,O′ coordinate to a wide range of cations whereas N coordination is limited to AgI, CuI or, in the case of less soft cations, to longer and presumably weaker contacts, e.g. to the more distant sites in Jahn–Teller distorted CuII. In contrast, pyridyl-substituted pentanediones act as N donor ligands, regardless whether their (H)acac site is chelating a cation or not. The still scarcely explored pyrazolyl derivative shows the most complex coordination pattern: it may be deprotonated both at the acetylacetone and the pyrazol site, the latter affording N,N′ bridging ligands. In addition to N donor nucleophilicity, the distance between the alternative coordination sites and their mutual orientation are relevant for crystal engineering applications.

Magnetic and Optical Properties of Novel Lanthanide(III) Complexes Based on Schiff Base and β-Diketonate Ligands

A series of lanthanide-based self-assembling complexes constructed from Schiff base and β-diketonate ligands have been synthesised by the same method. They are one dimensional complexes ({[Ln(H2L)(tta)2(OAc)]·0.5H2O}n (Ln = Eu (1), Gd (2), Dy (3), Yb (4)); H2L = N,N′-bis(salicylidene)butane-1,4-diamine, tta = 2-thenoyltrifluoroacetone). Complexes 1 and 4 exhibit characteristic metal-centred emission in the solid state. The lifetimes and quantum yields of luminescence were also determined. Magnetic analysis reveals that complex 3 exhibits field-induced single-molecule magnet (SMM) behaviour with an energy barrier of 24.07 K.

Chiral six-coordinate Dy(iii) and Tb(iii) complexes of an achiral ligand: structure, fluorescence, and magnetism

Two new chiral six-coordinate lanthanide complexes are obtained using an achiral ligand. Complex [Zn₃Dy] displays field-induced slow magnetization relaxation, while complex [Zn₃Tb] exhibits intense green photofluorescence and triboluminescence.

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

Four Ni^II–Cu^II–Ln^III 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.

Absolute Asymmetric Synthesis: Viedma Ripening of [Co(bpy)3](2+) and Solvent-Free Oxidation to [Co(bpy)3](3.)

Syntheses of [Co(bpy)3](2+) yield racemic solutions because the Δ- and Λ-enantiomers are stereochemically labile. However, crystallization and attrition-enhanced deracemization can give homochiral crystal batches of either handedness in quantitative yield. Subsequently, solvent-free oxidation with bromine vapour fixes the chirality because [Co(bipy)3](3+) does not enantiomerize in solution at ambient temperature. This combination of Viedma ripening and the labile/inert Co(II)/Co(III) couple constitutes a convenient method of absolute asymmetric synthesis.

Absolute asymmetric synthesis: protected substrate oxidation

Three new conglomerates incorporating bidentate sulfide ligands coordinated by Ru(II) centers have been prepared. Total spontaneous resolution by slow crystallization gives highly enantioenriched crystal batches, which are used in enantioselective oxidation of the sulfide ligands to give chiral sulfoxide complexes with >98 % ee. All relevant stereoisomers have been characterized by single-crystal X-ray diffraction, CD spectroscopy, and chiral HPLC. If the ligand range can be extended to monodentate sulfides, a large-scale and recyclable process for enantioselective oxidation of sulfides can be designed.

Absolute asymmetric synthesis of five-coordinate complexes

Three examples of optical resolution of five-coordinate complexes displaying only achiral mono- or bidentate ligands are reported.

New NIR-emissive tetranuclear Er(iii) complexes with 4-hydroxo-2,1,3-benzothiadiazolate and dibenzoylmethanide ligands: synthesis and characterization

Two new Er complexes were prepared and studied.

A missing link between chiral four- and five-coordinate complexes

A stereochemically labile complex, intermediate between square planar and distorted five-coordinate, was obtained in enantiomerically pure form through total spontaneous resolution.

Spontaneous resolution of chiral bis-sulfoxides with asymmetric atropisomerism

The atropisomeric ortho-disubstituted bis-sulfoxide (P/M,R,S)-3 with an asymmetric conformation adopts a homochiral right/left-handed supramolecular helix and exhibits an unprecedented spontaneous resolution.