Two Lanthanide(III) Complexes based on the Schiff Base N,N′‐Bis(salicylidene)‐1,5‐diamino‐3‐oxapentane: Synthesis,Characterization, DNA‐binding Properties,and Antioxidation

The Schiff base N,N′‐bis(salicylidene)‐1,5‐diamino‐3‐oxapentane (H₂L) and its lanthanide(III) complexes, PrL(NO₃)(DMF)(H₂O) ( 1 ) and Ho₂L₂(NO₃)₂ · 2H₂O ( 2 ), were synthesized and characterized by physicochemical and spectroscopic methods. Single crystal X‐ray structure analysis revealed that complex 1 is a discrete mononuclear species. The Pr^III ion is nine‐coordinate, forming a distorted capped square antiprismatic arrangement. Complex 2 is a centrosymmetric dinuclear neutral entity in which the Ho^III ion is eight‐coordinate with distorted square antiprismatic arrangement. The DNA‐binding properties of H₂L and its Ln^III complexes were investigated by spectrophotometric methods and viscosity measurements. The results suggest that the ligand H₂L and its Ln^III complexes both connect to DNA in a groove binding mode; the complexes bind more strongly to DNA than the ligand. Moreover, the antioxidant activities of the Ln^III complexes were in vitro determined by superoxide and hydroxyl radical scavenging methods, which indicate that complexes 1 and 2 have OH ^· and O₂^{– ·} radical scavenging activity.     

Coordinate Structures of PrIII, GdIII, TmIII, and YbIII Complexes with Nitrilotriacetic Acids

The crystal and molecular structures of the [Pr^III(nta)(H₂O)₂]·H₂O (nta = nitrilotriacetic acids), K₃[Gd^III(nta)₂(H₂O)]·6H₂O, and K₃[Yb^III(nta)₂]·5H₂O complexes have been determined by single-crystal X-ray structure analyses. In [Pr^III(nta)(H₂O)₂]·H₂O, the Pr^IIINO₈ part forms a nine-coordinate pseudo-monocapped square antiprismatic structure in which one N and three O atoms are from one nta ligand in the same molecule, three O atoms from another nta ligand in the neighboring molecule and two O atoms from two coordinate water molecules. In K₃[Gd^III(nta)₂(H₂O)]·6H₂O, the [Gd^III(nta)₂(H₂O)^3- complex anion has a nine-coordinate pseudo-monocapped square antiprismatic structure in which each nta acts as a tetradentate ligand with one N atom of the amino group and three O atoms of the carboxylic groups. In K₃[Yb^III(nta)₂]·5H₂O, each nta also acts as a tetradentate ligand with one N atom of amino group and three O atoms of the carboxylic groups, but the [Yb^III(nta)₂ ^3- complex anion has an eight-coordinate structure with a distorted square antiprismatic prism. All the results including those for [Tm^III(nta)(H₂O)₂]·2H₂O confirm the inferences on the coordinate structures and coordination numbers of rare earth metal complexes with the nta ligand.     

Syntheses,Structures, Magnetic Properties,and NIR Emission Properties of a Series of Novel 1, 2, 4, 5‐Cyclohexanetetracarboxylate‐bridged Lanthanide Complexes with 3D Framework Structures

Solvothermal combination of trivalent lanthanide metal precursors with 1, 2, 4, 5‐cyclohexanetetracarboxylic acid (L) ligand has afforded the preparation of a family of eight new coordination polymers [Ln₄(L)₃(H₂O)₁₀] · 7H₂O (Ln = Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) ( 1 – 8 ). Structural analyses reveal that the 1, 2, 4, 5‐cyclohexanetetracarboxylic acid ligand with e,a,a,e (L^I) conformation displays a μ₄‐(κ³O, O, O⁵)(κ²O²,O²)(κ²O⁴,O⁴)‐bridging mode to generate 3D frameworks of complexes 1 – 8 and the α‐Po topology with the short Schläfli symbol {4¹².6³} could be observed in complexes 1 – 8 . The near‐infrared luminescence properties were studied, and the results have shown that the Ho^III, Er^III, and Yb^III complexes emit typical near‐infrared luminescence in the solid‐state. Variable‐temperature magnetic susceptibility measurements of complexes 2 – 7 have shown that complex 2 (Gd) shows the ferromagnetic coupling between magnetic centers, whereas the complexes 3 – 7 show the antiferromagnetic coupling between magnetic centers. Additionally, the thermogravimetric analyses were discussed.     

Wavelength-Dependent Singlet Oxygen Generation in Luminescent Lanthanide Complexes with a Pyridine-Bis(Carboxamide)-Terthiophene Sensitizer

Lanthanide ion (Ln^III) complexes, [Ln(3Tcbx)₂]³⁺ (Ln^III=Yb^III, Nd^III, Er^III) are isolated with a new pyridine-bis(carboxamide)-based ligand with a 2,2′:5′,2′′-terthiophene pendant (3TCbx), and their resulting photophysical properties are explored. Upon excitation of the complexes at 490 nm, only Ln^III emission is observed with efficiencies of 0.29 % at 976 nm for Ln^III=Yb^III and 0.16 % at 1053 nm for Ln^III=Nd^III. Er^III emission is observed but weak. Upon excitation at 400 nm, concurrent ¹O₂ formation is seen, with efficiencies of 11 % for the Yb^III and Nd^III complexes and 13 % for the Er^III complex. Owing to the concurrent generation of ¹O₂, as expected, the efficiency of metal-centered emission decreases to 0.02 % for Yb^III and 0.05 % for Nd^III. The ability to control ¹O₂ generation through the excitation wavelength indicates that the incorporation of 2,2′:5′,2′′-terthiophene results in access to multiple sensitization pathways. These energy pathways are unraveled through transient absorption spectroscopy.     

Synthesis,crystal structures,and infrared spectroscopy of a series of lanthanide phosphonoacetate coordination polymers

Hydrothermal reactions of lanthanide chloride, phosphonoacetic acid (H₂O₃PCH₂COOH), and water in the presence of HCl provide a series of lanthanide coordination polymers. FT-IR spectra confirm that there are three kinds of structures among seven complexes, {[Ln₂(O₃PCH₂CO₂)₂(H₂O)₃]?·?H₂O}_∞ (type I) (Ln?=?La^III for 1; Pr^III for 2; Nd^III for 3 and Eu^III for 4), [Ln(O₃PCH₂CO₂)(H₂O)₂]_∞ (type II) (Ln?=?Tb^III for 5), and [Ln(O₃PCH₂CO₂)(H₂O)₂]_∞ (type III) (Ln?=?Ho^III for 6 and Yb^III for 7). Complexes 1–5 show 2-D 4,4,5,5-connected (4⁴?·?6²)(4⁵?·?6)(4⁶?·?6⁴)(4⁸?·?6²) topology networks and 2-D 4-connected (4⁴?·?6²) topology networks and then are further linked into 3-D supramolecular networks by hydrogen-bonding interactions; 6 and 7 both exhibit a 3-D 4-connected (4²?·?6³?·?8) topology with 1-D dumbbell-shaped channels. The results indicate infrared spectroscopy is in accord with the result of single-crystal X-ray analysis.     

Coordinated lanthanide metal complexes ofN-benzoylglycine hydrazide

Summary N-benzoylglycine hydrazide (BzGH) reacts with trivalent lanthanide metal ions forming complexes of the type [Ln(BzGH)₂Cl(H₂O)₂]Cl₂·nH₂O, where Ln=La^III, Pr^III, Nd^III, Sm^III, Eu^III, Gd^III, Tb^III, Dy^III, or Y^III;n=1 or 2. The structures of the complexes have been studied by conductance, magnetic, electronic, i.r.,¹H n.m.r. and¹³C n.m.r. spectral techniques. The nephelauxetic ratio, the bonding parameter, Sinha's parameter and the covalency angular overlap parameter have been calculated from the electronic spectra of Pr^III, Nd^III and Sm^III complexes. Seven-coordination is proposed in the Nd^III complex. The i.r. and¹H n.m.r. spectral data suggest bidentate BzGH in all the complexes.     

Synthesis and photophysical properties of Ir<Superscript>III</Superscript>-Ln<Superscript>III</Superscript> (Ln = Nd,Yb, Er) bimetallic complexes containing bipyrimidines as bridging ligands

Bipyrimidines have been chosen as (N∧N)(N∧N) bridging ligands for connecting metal centers. Ir^III-Ln^III (Ln = Nd, Yb, Er) bimetallic complexes [Ir(dfppy)₂(μ-bpm)Ln(TTA)₃]Cl were synthesized by using Ir(dfppy)₂(bpm)Cl as the ligand coordinating to lanthanide complexes Ln(TTA)₃·2H₂O. The stability constants between Ir(dfppy)₂(bpm)Cl and lanthanide ions were measured by fluorescence titration. The obvious quenching of visible emission from Ir^III complex in the Ir^III-Ln^III (Ln = Nd, Yb, Er) bimetallic complexes indicates that energy transfer occurred from Ir^III center to lanthanides. NIR emissions from Nd^III, Yb^III, and Er^III were obtained under the excitation of visible light by selective excitation of the Ir^III-based chromophore. It was proven that Ir(dfppy)₂(bpm)Cl as the ligand could effectively sensitize NIR emission from Nd^III, Yb^III, and Er^III.     

Aqua­tris­(1,10‐phenan­throline)­(trans‐2,3‐di­methyl­acrylato)­ytterbium(III)

The title mononuclear complex, [Yb(C₅H₇O₂)₃(C₁₂H₈N₂)(H₂O)], is a most uncommon carboxylate complex of a rare earth metal. Each Yb^III ion is eightfold coordinated, being bonded to five O atoms of three dimethylacrylate groups, both N atoms of a phenanthroline and one O atom of a water molecule, giving a distorted square antiprismatic coordination polyhedron.     

trans‐Chloro­bis­(ethyl­enedi­amine‐N,N′)­nitro­cobalt(III) perchlorate

In the title compound, trans‐[CoCl(NO₂)(C₂H₈N₂)₂]ClO₄, there are two independent Co^III complexes with a distorted octahedral coordination, and they show an orientational disorder such that the positions of the nitro and chloro ligands are exchanged. As a result, the averaged structure has inversion centres at the Co atoms. The perchlorate‐O atoms are disordered over two sites.     

Lanthanide and Transition Metal Complexes of Dialkyl α-Hydroxyiminophosphonates

Abstract

α-Hydroxyiminophosphonic acid derivatives are widely known not only as intermediates in the synthesis of the important aminophosphonic acids,^1,2 but also as phosphorylating agents,³ potential metalloenzyme inhibitors,⁴ and as compounds having fungicidal activity.⁵ In this work the scope of these compounds has been extended considerably by the synthesis of a number of novel dialkyl derivatives. Novel lanthanide (La^III, Pr^III, Nd^III, Gd^III and Dy^III) and transition metal (Co^II and Ni^III) complexes of dialkyl α-hydroxyiminophosphonates (RO)₂P(O)C(R')N(OH) where R = Et. Prⁱ and R′ = Me, Et have been prepared and the NMR shift properties of the Pr^III complex (R = Et; R′ = Et) indicate the potential of these compounds as NMR shift reagents for the analysis of geometric isomers.^6,7 X-ray crystal structure analysis of [Ni(L¹)₂C1₂] (L¹: R = Et; R′ = Et) shows a distorted cis octahedral coordination at the nickel atom giving two symmetry related diethyl-(E)-α-hydroxyiminopropanephosphonate ligands and two chlorine donors, and those of [Pr(L²)₃Cl₃] and [Nd(L²)₂(NO₃)₃(H₂O)] (L²: R = Prⁱ; R′ = Et) show nine-coordination geometries with asymmetric bidentate and monodentate L² bonding respectively. Thus the metal complexes show unusual coordination ambivalence, changing from symmetrically bidentate to asymmetrically bidentate and then to monodentate bonding modes, to accommodate the different steric requirements of the coordinating anions in facilitating neutral complex formation.     

Coordination chemistry of f-block elements with imine acids. Part IV. Synthetic and chiroptical studies on lanthanide(III) complexes of imine acids derived from L-alanine,L-valine,L-tyrosine and L-glutamic acid

Summary N-(orthovanillidene)L-alanine (OVAlaH₂), N-(salicylidene)L-valine (SValH₂), N-(orthovanillidene)L-valine (OVValH₂), N-(orthovanillidene)L-tyrosine (OVTyrH₃) and N-(salicylidene)L-glutamic acid (SGluH₃) react with La^III, Pr^III, Nd^III and Sm^III to yield new chiral complexes. Their dominant conformers were determined from c.d. spectra supported by¹H n.m.r. data, except for the L-glutamic acid derived complexes which were insoluble.     

Complexes of some 4f metal ions of the mesogenic Schiff-base,N,N′-di-(4-decyloxysalicylidene)-1′,3′-diaminobenzene: synthesis and spectral studies

A mesogenic Schiff-base, N,N′-di-(4-decyloxysalicylidene)-1′,3′-diaminobenzene, H₂ddsdbz (abbreviated as H₂L), that exhibits a nematic mesophase was synthesized and its structure was studied by elemental analysis, mass spectrometry, NMR, and IR spectral techniques. The Schiff-base, H₂L, upon condensation with hydrated lanthanide(III) nitrates yields Ln^III complexes, [Ln₂(LH₂)₃(NO₃)₄](NO₃)₂, where Ln?=?La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Ho. Analyses of the IR and NMR spectral data imply bidentate Schiff-base through two phenolate oxygen atoms in its zwitterionic form to Ln^III, rendering the overall geometry of the complexes as a seven-coordinate polyhedron – possibly distorted mono-capped octahedron. Polarizing optical microscope and differential scanning calorimetry studies reveal that despite H₂L being mesogenic, none of the Ln^III complexes synthesized under this study exhibits mesomorphism.     

Dye sensitization of a large band gap semiconductor by an iron(III) complex

The Fe(III) complex, [Fe^III(HQS)₃] (HQS = 8-hydroxyquinoline-5-sulfonic acid), is found to effect sensitization of the large band gap semiconductor, TiO₂. The role of interfacial electron transfer in sensitization of TiO₂ nanoparticles by surface adsorbed [Fe^III(HQS)₃] was studied using femtosecond time scale transient absorption spectroscopy. Electron injection has been confirmed by direct detection of the electron in the conduction band. A TiO₂-based dye-sensitized solar cell (DSSC) was fabricated using [Fe^III(HQS)₃] as a sensitizer, and the resulting DSSC exhibited an open-circuit voltage value of 425 mV. The value of the short-circuit photocurrent was found to be 2.5 mA/cm². The solar to electric power conversion efficiency of the [Fe^III(HQS)₃] sensitized TiO₂-based DSSC device was 0.75 %. The results are discussed in the context of sensitization of TiO₂ by other Fe(II)-dye complexes.     

Rare earth–porphyrin complex catalysts for transforming CO2 into cyclic carbonate under mild conditions

A series of rare earth metal complexes RE(TPP)(acac) (RE = Nd^III, Yb^III, Eu^III, Er^III, Pr^III, and Lu^III; TPP = 5,10,15,20-tetraphenylporphyrin) were synthesized and characterized via UV–vis, IR, and elemental analyses. Their catalytic activities on the synthesis of cyclic carbonates from carbon dioxide and epoxides under different reaction conditions (temperature, pressure, and reaction time) were investigated. Catalytic reaction tests showed that the complex Lu(TPP)(acac) could significantly enhance the catalytic reactivity under mild conditions without any co-solvent.     

One-dimensional chloro-bridged Cd(II) chains separated by dimethyl hexadecyl sulfonium cation layers: synthesis and structure

A low-dimensional material with the composition {(n-C₁₆H₃₃)(CH₃)₂S}_∞ ⁺¹[CdCl₃]^? has been prepared. As expected, the sulfonium cations form an insulating organic layer; the closest Cd–Cd distance between layers is about 19 Å, as compared to 3.9 Å within the same layer. The inorganic layer is formed by a 5-coordinated cadmium(II) moiety CdCl₅, connected to a one-dimensional chain of slightly distorted, edge-sharing square pyramids. The compound was synthesized from the parent sulfonium chloride and CdCl₂ in ethanol, exploiting the Lewis acidity of Cd(II).     

Binuclear ruthenium complexes containing mPTA and alkyl-bis(8-thiotheophylline) derivatives (mPTA = N-methyl-1,3,5-triaza-7-phosphaadamantane)

The water-soluble complex [RuClCp(PPh₃)(mPTA)](CF₃SO₃) reacts with the thiopurines, bis(S-8-thiotheophylline)methane (MBTTH₂), 1,2-bis(S-8-thiotheophylline)ethane (EBTTH₂), and 1,3-bis(S-8-thiotheophylline)propane (PBTTH₂), to lead to the binuclear ruthenium(II) complexes [{RuCp(PPh₃)(mPTA)}₂-μ-(L-κS7,S′7)](CF₃SO₃)₂ where (L = MBTT^2? (1), EBTT^2? (2), and PBTT^2? (3)). All the complexes have been fully characterized by elemental analysis, IR, and multinuclear ¹H, ¹³C{¹H}, and ³¹P{¹H} NMR spectroscopy. The cyclic voltammetry of the complexes is characterized by two one-electron oxidative responses (Ru^II–Ru^II/Ru^III–Ru^II; Ru^III–Ru^II/Ru^III–Ru^III) that increase their redox potential when the bis(8-thiotheophylline)-alkyl-bridge growths. The reactivity against DNA and partition coefficient of the complexes were also determined.     

Synthesis,Crystal Structure,and Electrochemistry of Iron and Cobalt Complexes Supported by a Pentadentate Amine‐bis(phenolate) Ligand

The pentadentate amine‐bis(phenolate) ligand 6,6′‐(dipyridin‐2‐ylmethylazanediyl)bis(methylene)bis(2,4‐dimethylphenol) (H₂L) was prepared and characterized. This ligand readily coordinates with Fe^III or Co^III ions, and the resulting complexes [Fe^IIILCl] ( 1 ) and [Co^IIIL(H₂O)]Cl ( 2 ) were characterized by elemental analysis. X‐ray structural studies show that the ligand in complexes 1 and 2 acts as a pentadentate ligand, leaving one coordination side of the transition metal available for exogenous ligands such as chloride ion ( 1 ) or water ( 2 ) ligand, and the central metal atoms are hexacoordinate in a similar distorted octahedral arrangement. Electrochemical studies reveal that each of the complexes exhibits multiple redox processes in the potential window investigated. Complex 1 shows one reversible oxidative event at 0.32 V and one quasi‐reversible reduction event at –1.03 V, while the complex 2 displays one reversible oxidative event at 0.18 V and one quasi‐reversible reduction at –0.64 V.     

The Building Block [FeIII(pzphen)(CN)4]– and its Lanthanide Complexes: Synthesis,Crystal Structure,and Magnetic Properties

The cyanide building block [Fe^III(pzphen)(CN)₄]^– and its four lanthanide complexes [{Fe^III(pzphen)(CN)₄}₂Ln^III(H₂O)₅(DMF)₃] · (NO₃) · 2(H₂O) · (CH₃CN) [Ln = Nd ( 1 ), Sm ( 2 ), DMF = dimethyl formamide] and [{Fe^III(pzphen)(CN)₄}₂Ln^III(NO₃)(H₂O)₂(DMF)₂](CH₃CN) [Ln = Gd ( 3 ), Dy ( 4 )] were synthesized and structurally characterized by single‐crystal X‐ray diffraction. Compounds 1 and 2 are ionic salts with two [Fe^III(pzphen)(CN)₄]^– cations and one Ln^III ion, but compounds 3 and 4 are cyano‐bridged Fe^III‐Ln^III heterometallic 3d‐4f complexes exhibiting a trinuclear structure in the same conditions. Magnetic studies show that compound 3 is antiferromagnetic between the central Fe^III and Gd^III atoms. Furthermore, the trinuclear cyano‐bridged Fe^III₂Dy^III compound 4 displays no single‐molecular magnets (SMMs) behavior by the alternating current magnetic susceptibility measurements.     

Synthesis,crystal structure,spectroscopy, and magnetism of a mixed valence Co(III)–Co(II)–Co(III) complex stabilized by N-(2-hydroxybenzyl)salicylaldimine

Reaction of Co(OAc)₂ · 4H₂O with N-(2-hydroxybenzyl)salicylaldimine (H₂L_a) in dimethylformamide (DMF)–H₂O yields a linear trinuclear mixed valence complex [Co^III(μ-L_a)(μ-L_b)(μ-OAc)]₂Co^II · 2DMF (1). Here, HL_b is salicylaldimine, which is afforded by an in situ transformation of H₂L_a via cleavage of the C–N bond. Complex 1 has been characterized by X-ray crystallography as well as elemental analysis, UV-Vis, and IR spectroscopy. The cathodic and anodic responses of 1 in DMF appeared at ?1.46 V (Co^III → Co^II, quasi-irreversible) and +0.99 V (Co^II → Co^III, irreversible) versus saturated calomel electrode, respectively. The magnetic behavior of 1 has been analyzed by the one-ion approximation with spin–orbit coupling in O_h symmetry giving λ = ?121 cm^?1.