Interactions of trivalent lanthanide cations with tetradentate Schiff bases. Synthesis and characterization of lanthanide(III) complexes with N,N′-bis(pyridin-2-ylmethylene)benzene-1,2-diamine

The novel lanthanide(III) complexes [La(NO₃)₃(H₂O)L] 1, and [Ln(NO₃)₃L] (Ln=Pr 2, Sm 3, Gd 4) where L=N,N^′-bis(pyridin-2-ylmethylene)benzene-1,2-diamine, have been obtained by direct reaction of the Schiff base ligand and the corresponding hydrated lanthanide(III) nitrates in methanol. All complexes were characterized spectroscopically and thermogravimetrically. Complex 3 was also characterized with crystallographic studies. In the molecular structure of 3, Sm(III) is surrounded by all four nitrogen atoms of the Schiff base and six oxygen atoms belonging to three bidentate chelating nitrato ligands.     

A Facile Access to New Polymethylmethacrylate-Anchored Ferrocene Substituted Nickel(II) Unsymmetrical Schiff Base Complexes: Synthesis and Characterization

This paper discloses two new side-chain metallopolymers containing an unsymmetrical organometallic Schiff base complex of Ni(II) linked to a polymethylmethacrylate (PMMA) matrix. The neutral ferrocene substituted Schiff base complex 1, Ni{CpFe(η⁵-C₅H₄)-C(O)CH=C(CH₃)N–o-C₆H₄N=CH-(2-O,5-OH-C₆H₃)} where (Cp = η⁵-C₅H₅), was synthesized via template reaction by condensation of the tridentate half-unit metalloligand Fc-C(O)CH=C(CH₃)-N(H)-o-C₆H₄NH₂ (Fc = ferrocenyl = CpFe(η⁵-C₅H₄)) with 2,5-dihydroxybenzaldehyde in the presence of nickel(II) acetate tetrahydrate. The binuclear Schiff base complex of Ni(II) containing an aromatic free hydroxyl group was reacted under basic conditions with PMMA to afford, upon trans-esterification reaction, metallopolymers 2 (complex 1 monomeric unit/PMMA = 1/5) and 3 (complex 1 monomeric unit/PMMA = 1/3). Elemental analysis, FT-IR, ¹H and ¹³C NMR spectroscopies, and cyclic voltammetry were utilized to characterize the newly synthetized compounds. Surface morphology of the metallopolymer film of 2 was studied using atomic force microscopy.     

Synthesis,crystal structures and NIR luminescence properties of binuclear lanthanide Schiff Base complexes

Three binuclear lanthanide complexes [Nd₂(L¹)₃(MeOH)]·MeOH·H₂O (1) and [Ln₂(H₂L²)₂(OAc)₄]·2(CF₃SO₃)·MeOH·EtOH (Ln = Nd (2) and Ho (3)) were prepared using two Schiff base ligands. Interestingly, 1 has a triple-decker structure with two lanthanide ions enclosed by three rigid conjugated Schiff base ligands (H₂L¹), while 2 and 3 show nanoscale ring structures (8 × 12 × 12 Å) formed by flexible long-chain Schiff base ligands (H₂L², ~ 23 Å) with the lanthanide ions located in the center. Upon excitation of the ligand-centered absorption bands, 1–2 and 3 show typical NIR emission spectra for Nd^3 + and Ho^3 + ions, respectively. In 1, the Nd(III) centers are shielded within the decker-like structure and surrounded by chromogenic Schiff base ligands (energy transfer donors). Luminescence studies show that the NIR emission lifetime of 1 is longer than that of 2 in solution.     

Fluorescence Properties Change of Lanthanide Coordination Polymers Dispersed in Mesoporous SBA-15 by Energy Transition Process

Four lanthanide coordination polymers, {[Ln(HPDA)(PDA)(H₂O)₂]·4H₂O} _n (Ln?=?Sm (1), Eu (2), Tb (3)) and {[Sm₃(H₂PDA)₂(HPDA)₂(PDA) (OH)₅(H₂O)₃]·2dta·4H₂O} _n (4) (H₂PDA?=?pyridine-2,6-dicarboxylic acid, dta?=?diethyl amine), have been synthesized under hydrothermal conditions and were characterized by elemental analysis, IR spectrometer, and single-crystal X-ray crystallography. In the complexes 1–3, the 1D chains are assembled into 2D layer by hydrogen bonds formed between the carboxyl groups, and were further assembled into 3D framework by hydrogen bonds and π–π stacking interactions. In complex 4, each Sm³⁺ ion connected to the neighboring Sm³⁺ ion through bridging carboxyl oxygen atoms, and then give rise to a new 2D layered open-framework structure. The 3D supramolecular structure of 4 is constructed through hydrogen-bonding and π–π stacking interactions between adjacent metal–organic polymeric coordination chains. Complexes 1–3 were dispersed in mesoporous materials SBA-15 in DMF solution (denoted as ML-SBA-15, ML?=?1, 2, 3), which were characterized by XRD, IR, and fluorescence spectra. Compared to the complexes 1–3, the photoluminescence efficiency of hybrid material was improved by the energy transition between mesoporous materials and the complexes. The complexes encapsulated in mesoporous materials SBA-15 exhibited stronger luminescence intensity and longer fluorescence lifetime.     

Four novel lanthanide(III) coordination polymers with 3D network structures containing 2-fold interpenetration

Four novel lanthanide(III) coordination polymers [Ln(L)_1.5(H₂O)₂]·5H₂O [Ln = Sm (1), Eu (2), Tb (3), Dy (4)] have been hydrothermally synthesized by the reaction of 1,2-bis[4-amino-5-carboxylmethylthio-(1,2,4-triazol-3-yl)]ethane (H₂L) with lanthanide(III) salts, and structurally characterized by single crystal X-ray diffraction. Polymers 1–4 are isostructural, in which all the Ln^III atoms are nine-coordinated and the carboxylate groups adopt three different coordination modes (bidentate chelate, bidentate bridging, bidentate chelate bridging) to connect Ln^III atoms. These polymers exhibit 3D network structures with 2-fold interpenetration, in which intriguing 1D channels are observed. Besides, the spectra properties of the title polymers are investigated, the strong luminescence characteristics of 2–3 are found.     

Six-coordinate oxo-vanadium(V) dimer complex with methoxy bridging: Synthesis,crystal structure,biological activity and molecular docking

A diketone-based tridentate Schiff base, 3-[(2-hydroxyphenyl)amino]-1,3-diphenylprop-2-en-1-one (H₂L), and its oxo-vanadium(V) dimer complex, [VO(L)(OMe)]₂, were synthesized and characterized using spectroscopic and physicochemical techniques. Single crystal X-ray diffraction indicated that the Schiff base ligand in its deprotonated form was found to bind to the V(V) ion through the azomethine nitrogen, amine and phenolic oxygens in a distorted octahedral geometry. The other positions around the V(V) center were occupied by an oxido group and two oxygens from methoxido ligands. Antimicrobial studies showed that the synthesized complex indicated significant antimicrobial activities against Escherichia coli (ATCC 25922) and Staphylococcus aureus (ATCC 33591 and 29213) bacteria while no antibacterial activity was observed for the ligand alone. The potential of [VO(L)(OMe)]₂ as an antimicrobial agent, was additionally investigated using molecular docking of the complex with GlcN-6-P synthase.     

A series of lanthanide (III) coordination polymers derived via in situ hydrothermal decarboxylation of quinoline-2,3-dicarboxylic acid

A series of one-dimensional coordination polymers assembled from LnNO₃ · 6H₂O (Ln = Sm(1), Eu(2), Tb(3), La(4), Ce(5), Pr(6), Nd(7), Dy(8)), quinoline-2,3-dicarboxylic acid (2,3-H₂qldc) and 1,10-phenanthroline (phen) formulated as [Ln(2,3-qldc)(3-qlc)(phen)]_n (3-Hqlc = quinoline-3-carboxylic acid) were obtained under hydrothermal conditions. It is remarkable that in situ hydrothermal decarboxylation was observed during preparing these polymers. Complexes 1–8 were characterized by elemental analyses, IR spectroscopy and single crystal X-ray diffraction analyses. The thermal stabilities and photoluminescence properties of these complexes have been investigated.     

Novel luminescent heterobimetallic Ln–Cu(I) 3D coordination polymers based on 5-(4-pyridyl) isophthalic acid as heteroleptic ligand. Synthesis and structural characterization

Six novel photoluminescent Ln–Cu(I) heterobimetallic 3D coordination polymers, [LnCu (pyip^2 −)₂(H₂O)]_n (1–6) (where Ln is Pr, Nd, Sm, Eu, Gd, Ho, respectively, and H₂pyip = 5-(4-pyridyl) isophthalic acid) have been synthesized in a concise and reproducible manner under hydrothermal conditions. All of these substances were fully characterized by appropriate spectroscopic methods and elemental analysis. Structural determinations revealed that 1–6 are isomorphic and display 3D frameworks. Luminescent properties of the obtained compounds have been studied in detail revealing light emissions of warm white, cool white and light blue for 3, 4 and 5, respectively. The effectiveness of association of a rare earth with a transition metal in producing valuable luminescent materials for practical applications is demonstrated.     

Bis(cyclopentadienyl) lanthanide benzylthiolate: synthesis,molecular structure and catalytic property for ε-caprolactone –polymerization

Reaction of LnCl₃ first with three equivalent of C₅H₅Na in THF, then with one equivalent of benzyl mercaptan, led to complexes of [(C₅H₅)₂Ln(SCH₂Ph)]₂ (Ln?=?Sm(1), Yb(2)), being characterized by infrared spectra, elemental analyses and X-ray crystallography for 2. Complex 2 is a dimer with two thiolate ligands as bridging groups in eight coordinate. The Yb-S(benzyl) bonds in 2 (2.703(19) and 2.719(2) Å, respectively) were longer than the Yb-S(aryl) bonds (about 2.640 Å) in analogous complexes. The catalytic property for the polymerization of ε-caprolactone by 1 and 2 was studied. Similar experiment was also made with [(C₅H₅)₂Ln(SPh-p-CH₃)(THF)]₂ (Ln?=?Sm(3), Yb(4)) for comparison. It was found that complex 2 showed the activity best, and the activity decreased in the order of 2?>?3?>?1?>?4. When [ε-CL]₀/[Ln] was 500 and the polymerization temperature was 35°C, complex 2 catalyzed the polymerization in living character, which could not be achieved by lanthanide arylthiolates such as 3 and 4.     

Salen-Type Lanthanide Complexes with Luminescence and Near-Infrared (NIR) Properties

Two type lanthanide complexes obtained by salen-type ligand N,N’-ethylenebis(salicylideneimine) (H₂L^a) and N,N’-ethylene-bis(3-methoxysalicylideneimine) (H₂L^b) have been isolated. They are 2D coordination polymer [Yb(H₂L^a)_1.5(NO₃)₃] _n (1), mononuclear Ln(H₂L^b)(NO₃)₃ [Ln = Sm (2), Ho (3)]. The structures of 1–3 were determined by single crystal X-ray crystallographic studies and their photophysical properties were investigated.     

Hexanuclear 4d–4f complexes [Ln2Ag4(ina)8(H2O)10][NO3]2 · 4H2O (Ln = Sm, Eu, Dy): Syntheses, structures and photoluminescent properties

Hexanuclear 4d–4f heterometallic complexes, [Ln₂Ag₄(ina)₈(H₂O)₁₀][NO₃] ₂ · 4H₂O [Ln = Sm (1), Eu (2), Dy (3) and Hina = isonicotinic acid], have been synthesized by the hydrothermal reaction of lanthanide oxides, Ag^I, and isonicotinic acid at a suitable temperature. Single-crystal X-ray diffraction studies indicate that these 4d–4f complexes consist of extended 1D zigzag chains structure built upon [Sm₂Ag₄(ina)₈(H₂O)₁₀] subunits connected by Ag–Ag interactions. Furthermore, the photoluminescent properties of the complex 2 were studied.     

Electrochemical anion recognition by redox-responsive unnatural amino acid derivatives; the X-ray crystal structure of N-ferrocenoyl glycine methyl ester, (η5-C5H5)Fe(η5-C5H4)CONHCH2COOMe

N-Ferrocenoyl glycine ester derivatives FcCONHCH₂COOR (Fc=(η⁵-C₅H₅)Fe(η⁵-C₅H₄); R=methyl (1), ethyl (2) and benzyl (3)) have been prepared by coupling ferrocene carboxylic acid to a series of glycine esters using 1,3-dicyclohexylcarbodiimide (DCC), 1-hydroxybenzotriazole (HOBT) and Et₃N in CH₂Cl₂. The electrochemical anion sensing using a platinum microdisk working electrode of these N-ferrocenoyl glycine ester derivatives is reported. The crystal structure of 1 has been determined; principal dimensions are amide N(H)CO 1.229(3) Å, ester CO 1.183(3) Å with N–H⋯OC(amide) as the primary intermolecular hydrogen bond, N⋯O 2.804(3) Å.     

Synthesis, crystal structures and photoluminescence of Zn–Ln heterometallic polymers based on pyridine-2,3-dicarboxylic acid

Three new two-dimensional 3d–4f isostructural heterometallic coordination polymers, namely [Ln₂Zn(2,3-pydc)₄(H₂O)₄·4H₂O]_n (Ln = Sm (1), Eu (2), Gd (3), 2,3-pydcH₂ = pyridine-2,3-dicarboxylic acid) have been successfully synthesized by the hydrothermal reactions of Ln₂O₃, Zn(NO₃)₂·6H₂O, H₂pydc and H₂O. X-ray diffraction analyses reveal that they possess a 2D heterometallic framework containing 1D lanthanide chains based on dimeric [Ln(2,3-pydc)₂(H₂O)₂]₂ unit. The Zn(II) ion, which is six-coordinated by four oxygen and two nitrogen atoms from four 2,3-pydc²⁻ ligands, as a bridge, links the lanthanide chains to make the 1D chains further extend into 2D layer framework. Furthermore, the neighboring layers are assembled into three-dimensional supramolecular network through inter-layer O–HO and C–HO hydrogen-bond interactions. In addition, the solid-state luminescent property of complex 2 was investigated.     

Coordination polymers from 1-D to 3-D assembled from disulfonate ligands: Structures and luminescent properties

Four rare earth organodisulfonate coordination polymers, {[Tb₂(phen)₄(nds)₃(H₂O)₂]·4H₂O}_n (1), {[Ln(phen)(nds)(OH)]}_n[Ln = Sm (2), Nd (3)], {[Tb(phen)₂(nds)_0.5(OH)·H₂O]·(nds)_0.5}_n (4), were synthesized under the solvothermal conditions by using ligands 2,6-naphthalenedisulfonate (L = nds) and 1,10-phenanthroline (L′ = phen). Single-crystal X-ray diffraction reveals that compounds 1 and 4 exhibit different 1-D and 2-D crystal structures just owing to the single difference of stoichiometric ratio of the reactants in the synthesis process. Compounds 2 and 3 show 3-D structures with similar Ln coordination mode. Besides, the photoluminescent property in solid state of 1 was investigated in detail.     

X-ray structure and spectroscopic properties of some lanthanides(III) complexes derived from 2,6-diacetylpyridine-bis(benzoylhydrazone)

A series of trivalent lanthanide complexes of type [Ln(L) NO₃)(S)_n](NO₃)_m(S^′)_n, have been synthesized by the reaction of 2,6-diacetylpyridine-bis-(benzoylhydrazone) (H₂L) with lanthanide(III) nitrates in ethanol. These complexes have been characterized by analysis, molar conductance, magnetic measurements, infrared spectral studies and X-ray diffraction. The analytical data revealed the formation of 1:1 (metal:ligand) stoichiometry. Molar conductance in dmf gives 2:1 electrolytes in all the complexes. Magnetic moment values are close proximity of the Van Vleck values. IR study suggests the coordination of the ligand through the azomethine and the oxygen of the hydrazonic moiety. The nitrate ion is also found to be bidentate in all the complexes. The crystal structures were determined. 6, C₂₇H₃₁N₆O₇S₂Gd: a=b=8.6821(4) Å, c=84.363(5) Å, tetragonal P4₁2₁2 and Z=8. bf 7, C₂₅H₂₅N₆O₆SDy: a=11.750(3) Å, b=13.250(3) Å, c=36.000(6) Å, β=98.50(2), monoclinic, C2/c, Z=8. 9, C₂₄H₂₅N₆O₇Yb: a=10.750(2) Å, b=17.750(3) Å, c=14.250(4) Å, β=99.00(2), monoclinic, P2₁/n, Z=4. In these complexes the lanthanide ion assumes a nine coordinated geometry for Gd and an eight coordinated geometry for Dy and Yb.     

In situ synthesis and dielectric properties of copper(II) and nickel(II) chiral Schiff base complexes

Two chiral Schiff base-containing complexes, [Cu(L¹)](ClO₄)₂·H₂O (1, L¹ = (S,S)-N1,N2-bis((1H-imidazol-4-yl)methylene)cyclohexane-1,2-diamine) and [Ni(L²)₂](ClO₄)₂ (2, L² = (S,S)-N1-((1H-imidazol-4-yl)methylene)cyclohexane-1,2-diamine) were synthesized from the reaction mixture of 1H-imidazole-4-carbaldehyde, (S,S)-1,2-diaminocyclohexane and Cu(ClO₄)₂·6H₂O or Ni(ClO₄)₂·6H₂O in methanol. Single-crystal X-ray diffraction analyses reveal that the in situ generated chiral Schiff base ligands L¹ and L² are bisubstituted and monosubstituted, respectively, corresponding to the different metal ions Cu^II and Ni^II. Variable-frequency and -temperature dielectric properties of 1 and 2 have been studied.     

The synthesis and crystal structure of [M{H2B(tz*)2}2(H2O)] (M=Cu,Zn and tz*=3,5-dimethyl-1,2,4-triazole)

New ligand [KH₂B(tz^*)₂] (tz*=3,5-dimethyl-1,2,4-triazolyl) has been synthesized and the reactions of two different metal salts (copper and zinc) with the new ligand in agar gave two similar crystalline polymorphic forms: [Cu{H₂B(tz^*)₂}₂(H₂O)] (1) and [Zn{H₂B(tz^*)₂}₂(H₂O)] (2). A single crystal X-ray study revealed that the compound 1 was the monoclinic system with space group C2/c and a=8.462(3) Å, b=14.039(6) Å, c=19.991(8) Å, β=94.622(7)°, Z=4, R₁=0.0451, wR₂=0.1110. And the compound 2 was the monoclinic system with space group C2/c and a=8.4214(4) Å, b=13.8765(7) Å, c=20.2969(6) Å, β=95.615(2)°, Z=4, R₁=0.0667, wR₂=0.1375. The metal(II) ion in the complex is five-coordinated with four nitrogen atoms which come from triazolyl and one oxygen atom which come from water molecular. In both compounds, the hydrogen atoms of water molecule are connected by hydrogen bonding with N atoms of two adjacent complex molecules to form 2-D planes. The spectroscopic results are consistent with the crystallographic study.     

Synthesis,X-ray structure and catalytic properties of a copper(II) Schiff base complex modeling the activity of the CuB site of dopamine β-hydroxylase

The copper(II) complex [Cu(salgly)(bpy)]·4H₂O (1), where salgly is a tridentate glycinatosalicylaldimine Schiff base ligand, is prepared and structurally characterized. The complex is found to be catalytically active in the oxidation of ascorbic acid by dioxygen and the process is also effective in the presence of benzylamine giving benzaldehyde as a product, thus modeling the activity of the Cu_B site of dopamine β-hydroxylase.     

A Series of Luminescent Lanthanide–Organic Complexes Constructed from In Situ Generated Dithiobenzoic Acid

Two types of lanthanide thiolato-carboxylate complexes, [Type I: [Yb(dtba) (Hdtba)] _n (1), Type II: [Ln(dtba)_1.5(biim)] _n (Ln = Pr (2a), Nd (2b), Sm (2c), Eu (2d), Gd (2e), Tb (2f), Dy (2g), H₂dtba = 2,2′-dithiodibenzoic acid, bimm = diimidazole)] have been obtained by hydrothermal method and characterized by the single-crystal X-ray diffraction, IR, 2D-COS IR, TG and the luminescence analysis. The H₂dtba ligand came from the in situ S–S function reaction of 2-mercaptobenzoic acid (H₂mba) under the hydrothermal condition. Complex 1 is a 2D bamboo-like sqr-topology layered structure, and the 3D (4, 4, 6)-connected supramolecular frameworks is produced by the hydrogen bonds of O–H···O. Complexes of type II (from 2a to 2g) are isostructural and they are assigned to 1D rope-like chains by introducing the chelating ligand of diimidazole. These 1D rope-like chains are further linked by N–H···O hydrogen bonds into a 3D supramolecular framework with CdSO₄-type topology. Photoluminescence studies reveal that complexes 2b, 2c, 2d, 2f, 2g exhibit strong lanthanide characteristic emission bands in the solid state at room temperature.     

A new cyclic binuclear Ni(II) complex as a catalyst towards nitroaldol (Henry) reaction

A new cyclic binuclear Ni(II) complex, [Ni₂(H₂L)₂] · 4MeOH (1), has been synthesized using the Schiff base N′¹,N′³-bis(2-hydroxybenzylidene)malonohydrazide (H₄L). The X-ray crystal structure of 1 shows that the ligand coordinates in the dianionic keto form (H₂L^2 −) via mutual sharing of two Ni(II) ions. Complex 1 acts as a heterogeneous catalyst for the Henry reaction in water. A maximum conversion of ca. 93% was obtained under optimized conditions.