Chelation of ThIV, EuIII and NdIII by dianionic N,N′-bis(pyridoxylideneiminato)ethylene, (Pyr2en)2−. On the search of feasible modelings for heavy metals damage inhibition in living beings

A highly selective pyridoxal-based chemosensor for the detection of Zn(ii) and application in live-cell imaging; X-ray crystallography of pyridoxal-TRIS Schiff-base Zn(ii) and Cu(ii) complexes

In a simple, one-step reaction, we have synthesized a pyridoxal-based chemosensor by reacting tris(hydroxymethyl)aminomethane (TRIS) together with pyridoxal hydrochloride to yield a Schiff-base ligand that is highly selective for the detection of Zn(ii) ion. Both the ligand and the Zn(ii) complex have been characterized by ¹H & ¹³C NMR, ESI-MS, CHN analyses, and X-ray crystallography. The optical properties of the synthesized ligand were investigated in an aqueous buffer solution and found to be highly selective and sensitive toward Zn(ii) ion through a fluorescence turn-on response. The competition studies reveal the response for zinc ion is unaffected by all alkali and alkaline earth metals; and suppressed by Cu(ii) ion. The ligand itself shows a weak fluorescence intensity (quantum yield, Φ = 0.04), and the addition of zinc ion enhanced the fluorescence intensity 12-fold (quantum yield, Φ = 0.48). The detection limit for zinc ion was 2.77 × 10⁻⁸ M, which is significantly lower than the WHO's guideline (76.5 μM). Addition of EDTA to a solution containing the ligand–Zn(ii) complex quenched the fluorescence, indicating the reversibility of Zn(ii) binding. Stoichiometric studies indicated the formation of a 2 : 1 L₂Zn complex with a binding constant of 1.2 × 10⁹ M⁻² (±25%). The crystal structure of the zinc complex shows the same hydrated L₂Zn complex, with Zn(ii) ion binding with an octahedral coordination geometry. We also synthesized the copper(ii) complex of the ligand, and the crystal structure showed the formation of a 1 : 1 adduct, revealing 1-dimensional polymeric networks with octahedral coordinated Cu(ii). The ligand was employed as a sensor to detect zinc ion in HEK293 cell lines derived from human embryonic kidney cells grown in tissue culture which showed strong luminescence in the presence of Zn(ii). We believe that the outstanding turn-on response, sensitivity, selectivity, lower detection limit, and reversibility toward zinc ion will find further application in chemical and biological science.

The synthesis, characterization, X-ray crystallography, and live-cell imaging of pyridoxal-TRIS Schiff-base ligand which is selective as a luminescence sensor to detect Zn(ii) ion, and the corresponding Zn(ii) and Cu(ii) complexes are described.

Oligonuclear Actinoid Complexes with Schiff Bases as Ligands-Older Achievements and Recent Progress

Even 155 years after their first synthesis, Schiff bases continue to surprise inorganic chemists. Schiff-base ligands have played a major role in the development of modern coordination chemistry because of their relevance to a number of interdisciplinary research fields. The chemistry, properties and applications of transition metal and lanthanoid complexes with Schiff-base ligands are now quite mature. On the contrary, the coordination chemistry of Schiff bases with actinoid (5f-metal) ions is an emerging area, and impressive research discoveries have appeared in the last 10 years or so. The chemistry of actinoid ions continues to attract the intense interest of many inorganic groups around the world. Important scientific challenges are the understanding the basic chemistry associated with handling and recycling of nuclear materials; investigating the redox properties of these elements and the formation of complexes with unusual metal oxidation states; discovering materials for the recovery of trans-{U^VIO₂}²⁺ from the oceans; elucidating and manipulating actinoid-element multiple bonds; discovering methods to carry out multi-electron reactions; and improving the 5f-metal ions’ potential for activation of small molecules. The study of 5f-metal complexes with Schiff-base ligands is a currently “hot” topic for a variety of reasons, including issues of synthetic inorganic chemistry, metalosupramolecular chemistry, homogeneous catalysis, separation strategies for nuclear fuel processing and nuclear waste management, bioinorganic and environmental chemistry, materials chemistry and theoretical chemistry. This almost-comprehensive review, covers aspects of synthetic chemistry, reactivity and the properties of dinuclear and oligonuclear actinoid complexes based on Schiff-base ligands. Our work focuses on the significant advances that have occurred since 2000, with special attention on recent developments. The review is divided into eight sections (chapters). After an introductory section describing the organization of the scientific information, Sections 2 and 3 deal with general information about Schiff bases and their coordination chemistry, and the chemistry of actinoids, respectively. Section 4 highlights the relevance of Schiff bases to actinoid chemistry. Sections 5–7 are the “main menu” of the scientific meal of this review. The discussion is arranged according the actinoid (only for Np, Th and U are Schiff-base complexes known). Sections 5 and 7 are further arranged into parts according to the oxidation states of Np and U, respectively, because the coordination chemistry of these metals is very much dependent on their oxidation state. In Section 8, some concluding comments are presented and a brief prognosis for the future is attempted.

Tetranuclear oxido-bridged thorium(iv) clusters obtained using tridentate Schiff bases

Thorium(iv) complexes are currently attracting intense attention from inorganic chemists due to the development of liquid-fluoride thorium reactors and the fact that thorium(iv) is often used as a model system for the study of the more radioactive Np(iv) and Pu(iv). Schiff-base complexes of tetravalent actinides are useful for the development of new separation strategies in nuclear fuel processing and nuclear waste management. Thorium(iv)-Schiff base complexes find applications in the colorimetric detection of this toxic metal ion and the construction of fluorescent on/off sensors for Th(iv) exploiting the ligand-based light emission of its complexes. Clusters of Th(iv) with hydroxide, oxide or peroxide bridges are also relevant to the environmental and geological chemistry of this metal ion. The reactions between Th(NO₃)₄·5H₂O and N-salicylidene-o-aminophenol (LH₂) and N-salicylidene-o-amino-4-methylphenol (L'H₂) in MeCN have provided access to complexes [Th₄O(NO₃)₂(LH)₂(L)₅] (1) and [Th₄O(NO₃)₂(L'H)₂(L')₅] (2) in moderate yields. The structures of 1·4MeCN and 2·2.4 MeCN have been determined by single-crystal X-ray crystallography. The complexes have similar molecular structures possessing the {Th₄(μ₄-O)(μ-OR')₈} core that contains the extremely rare {Th₄(μ₄-O)} unit. The four Th^IV atoms are arranged at the vertexes of a distorted tetrahedron with a central μ₄-O^2- ion bonded to each metal ion. The H atom of one of the acidic -OH groups of each 3.21 LH^- or L'H^- ligand is located on the imine nitrogen atom, thus blocking its coordination. The Th^IV centres are also held together by one 3.221 L^2- or (L')^2- group and four 2.211 L^2- or (L')^2- ligands. The metal ions adopt three different coordination numbers (8, 9, and 10) with a total of four coordination geometries (triangular dodecahedral, muffin, biaugmented trigonal prismatic, and sphenocorona). A variety of H-bonding interactions create 1D chains and 2D layers in the crystal structures of 1·4 MeCN and 2·2.4 MeCN, respectively. The structures of the complexes are compared with those of the uranyl complexes with the same or similar ligands. Solid-state and IR data are discussed in terms of the coordination mode of the organic ligands and the nitrato groups. ¹H NMR data suggest that solid-state structures are not retained in DMSO. The solid complexes emit green light at room temperature upon excitation at 400 nm, the emission being ligand-centered.

Synthesis, X-ray structural features, DFT calculations and fluorescence studies of a new pyridoxal-benzimidazole ligand and its respective molybdenum complex

Studies based on FPDFT helped us to elucidate the reaction mechanism involving the BIMIPY–H⁺ + (MoO₂⁺²) species in the first complexation of molybdenum by a vitamin B6 constituent.

Photoluminescent nano-sized ternary and quaternary complexes of thorium(IV)

Some ternary and quaternary complexes of thorium(IV) with the general formula [Th(OOCCH3)2−n (SB) n (OOCC15H31)2] (HSB=Schiff bases and n=1 or 2) have been synthesized by the stepwise substitutions of acetate ions from thorium(IV) acetate, first with straight chain carboxylic acid and then with Schiff bases. The complexes are characterized by elemental analyses, spectral (electronic, infrared, 1H NMR, FAB mass, photoluminescence and powder XRD) and TEM studies. Conductance measurements indicated non-conducting behaviour of the complexes. Structural parameters from powder XRD data for complexes 5 and 6 which indicate poorly crystalline nano-sized triclinic particles. Electronic absorption spectra of the complexes showed π→π * and n→π * charge transfer transitions. All complexes displayed fluorescence and a correlation was sought between luminescence spectra of complexes in solution at room temperature. On the basis of physico-chemical studies, coordination number 8 was assigned for thorium(IV) in the complexes. The morphology and microstructure of the complexes were examined with transmission electron microscopy (TEM) and the selected area electron diffraction (SAED).

The influence of linker geometry in bis(3-hydroxy-N-methyl-pyridin-2-one) ligands on solution phase uranyl affinity

Seven water-soluble, tetradentate bis(3-hydroxy-N-methyl-pyridin-2-one) (bis-Me-3,2-HOPO) ligands were synthesized that vary only in linker geometry and rigidity. Solution-phase thermodynamic measurements were conducted between pH 1.6 and pH 9.0 to determine the effects of these variations on proton and uranyl cation affinity. Proton affinity decreases by introduction of the solubilizing triethylene glycol group as compared to unsubstituted reference ligands. Uranyl affinity was found to follow no discernable trends with incremental geometric modification. The butyl-linked 4 li-Me-3,2-HOPO ligand exhibited the highest uranyl affinity, consistent with prior in vivo decorporation results. Of the rigidly-linked ligands, the o-phenylene linker imparted the best uranyl affinity to the bis-Me-3,2-HOPO ligand platform.

Synthesis and characterization of new ion-imprinted polymer for separation and preconcentration of uranyl (UO2(2+)) ions

UO(2)(2+) ion-imprinted polymer materials used for solid-phase extraction were prepared by copolymerization of a ternary complex of uranyl ions with styrene and divinyl benzene in the presence of 2,2'-azobisisobutyronitrile. The imprinted particles were leached by HCl 6M. Various parameters in polymerization steps such as DVB/STY ratio, time of polymerization and temperature of polymerization were varied to achieve the most efficient uranyl-imprinted polymer. X-ray diffraction (XRD), infra-red spectroscopy (IR), thermo gravimetric analysis (TGA), UV-vis and nitrogen sorption were used to characterize the polymer particles. The XRD results showed that uranyl ions were completely removed from the polymer after leaching process. IR Analysis indicated that the N,N'-ethylenebis(pyridoxylideneiminato) remained intact in the polymer even after leaching. Some parameters such as pH, weight of the polymer, elution time, eluent volume and aqueous phase volume which affects the efficiency of the polymer were studied.