Revitalisation of group IV metal-oxo clusters: synthetic approaches, structural motifs and applications.

Group (IV) metal oxo clusters represent a unique family of molecular species that are increasingly being utilized in applications ranging from catalysis and materials chemistry to electronics, and sensors. These clusters exhibit distinctive structural features, chemical reactivity, and electronic structure. Nevertheless, their full potential has yet to be fully realized due to the lack of deeper understanding regarding their structure and formation mechanisms, inherent traits, and intricacies in their design, which could ultimately enable significant customization of their properties and overall behaviour.

The Identification of Structural Changes in the Lithium Hexamethyldisilazide-Toluene System via Ultrasonic Relaxation Spectroscopy and Theoretical Calculations.

Ultrasonic absorption measurements were carried out over a wide concentration and temperature range by means of a pulse technique to examine the structural mechanisms and the dynamical properties in thium exaethyliilazide (LiHMDS)-toluene solutions. Acoustic spectra revealed two distinct Debye-type relaxational absorptions attributed to the formation of trimers from dimeric and monomer units and to the formation of aggregates between a LiHMDS dimer and one toluene molecule in low and high frequencies, respectively. The formation of aggregates was clarified by means of molecular docking and DFT methodologies.

Experimental and Theoretical Investigation of the Mechanism of the Reduction of O from Air to O by VO-,,-Amidate Compounds and Their Potential Use in Fuel Cells.

The two-electron reductive activation of O to O is of particular interest to the scientific community mainly due to the use of peroxides as green oxidants and in powerful fuel cells. Despite of the great importance of vanadium(IV) species to activate the two-electron reductive activation of O, the mechanism is still unclear. Reaction of VO species with the tridentate-planar carboxamide (ΗL) ligands in solution (CHOH:HO) under atmospheric O, at room temperature, resulted in the quick formation of [V(═O)(η-O)(κ-L)(HO)] and -[V(═O)(κ-L)] compounds.

Identification of Aggregation Processes in Hexamethylenetetramine Aqueous Solutions: A Comprehensive Raman and Acoustic Spectroscopic Study Combined with Density Functional Theory Calculations.

Raman scattering has been employed to study in detail the concentration dependence of the vibrational modes for hexamethylenetetramine (HMTA) aqueous solutions. The formation of protonated and/or aggregated species has been clarified by comparing the experimental with the theoretically predicted vibrational spectra by means of quantum mechanical calculations. The analysis has shown that the vibrational modes of the solutions arise from a contribution of the vibrational modes of the HMTA self-aggregates and hetero-aggregates of HMTA with water molecules that are formed in the low- and intermediate-concentration regions, respectively.

Design and Modulation of Selectivity toward Vanadium(V) and Uranium(VI) Ions: Coordination Properties and Affinity of Hydroxylamino-Triazine Siderophores.

Based on the strong binding and high selectivity properties of 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine (Hbihyat) for [UO], novel binucleating ligands (BLs) ,',″,-((1,4-phenylenebis(oxy))bis(1,3,5-triazine-6,2,4-triyl))tetrakis(-methylhydroxylamine) (Hqtn), ,-bis(4,6-bis(hydroxy(methyl)amino)-1,3,5-triazin-2-yl)benzene-1,4-diamine (Hpdl), and ,-bis(4,6-bis(hydroxy(methyl)amino)-1,3,5-triazin-2-yl)ethane-1,2-diamine (Henl) were synthesized. Binuclear complexes formed by coordination of hard metal ions with Hqtn are thermodynamically more stable than their mononuclear analogues with Hbihyat due to the increase in entropy accompanying the formation of more chelate rings. Reaction of either Hqtn or Hpdl or Henl with [UO] and [VO] resulted in the isolation of the binuclear complexes [(UO)(μ-qtn)(HO)] (), [(VO)(μ-qtn)][PPh][PPh4] (), [(UO)(μ-pdl)(HO)(MeOH)] (), [(VO)(μ-pdl)][PPh] (), [(UO)(μ-enl)(HO)] (), and [(VO)(μ-enl)][PPh] ().

Hafnium(IV) Chemistry with Imide-Dioxime and Catecholate-Oxime Ligands: Unique {Hf} and Metalloaromatic {Hf}-Oxo Clusters Exhibiting Fluorescence.

Hafnium(IV) molecular species have gained increasing attention due to their numerous applications ranging from high-resolution nanolithography, heterogeneous catalysis, and electronics to the design of molecule-based building blocks in metal-organic frameworks (MOFs), with applications in gas separation, sorption, luminescence sensing, and interim storage of radioactive waste. Despite great potential, their chemistry is relatively underdeveloped. Here, we use strong chelators (2-6)-piperidine-2,6-dione (Hpidiox) and 2,3-dihydroxybenzaldehyde oxime (Hdihybo) to synthesize the first ever reported pentanuclear {Hf/Hpidiox} and hexanuclear {Hf/Hdihybo} clusters (HfOCs).

A Combined Experimental and Theoretical Investigation of Oxidation Catalysis by -[V(O)(Cl/F)(N)] Species Mimicking the Active Center of Metal-Enzymes.

Reaction of VOCl with the nonplanar tetradentate N bis-quinoline ligands yielded four oxidovanadium(IV) compounds of the general formula -[V(O)(Cl)(N)]Cl. Sequential treatment of the two nonmethylated N oxidovanadium(IV) compounds with KF and NaClO resulted in the isolation of the species with the general formula -[V(O)(F)(N)]ClO. In marked contrast, the methylated N oxidovanadium(IV) derivatives are inert toward KF reaction due to steric hindrance, as evidenced by EPR and theoretical calculations.

Acid/base responsive assembly/dis-assembly of a family of zirconium(IV) clusters with a cyclic imide-dioxime ligand.

The hydrolytically stable dioxime ligand (2-6)-piperidine-2,6-dione (Hpidiox) acts as a strong chelator mainly with hard metals in high oxidation states, a pre-requisite for potential applications in metal sequestering processes from aqueous solutions. Reaction of ZrCl with Hpidiox in methanol gives the mononuclear compound [Zr(η,η,η-Hpidiox-,,')(OH)]Cl·HO·CHOH (1), while the same reaction mixture in the presence of KOH gave the pentanuclear ZrOC [ZrIV5(μ-OH)(OH)(μ-η,η,η-Hpidiox-,,')(η,η,η-Hpidiox,,')]·5KCl·3CHOH·8HO (2). Compound 1 is formed at very acidic pH = 0, and the pentanuclear ZrOC 2 at higher pH values (pH = 2).

Synthesis, Structural and Physicochemical Characterization of a Titanium(IV) Compound with the Hydroxamate Ligand ,2-Dihydroxybenzamide.

The siderophore organic ligand ,2-dihydroxybenzamide (Hdihybe) incorporates the hydroxamate group, in addition to the phenoxy group in the ortho-position and reveals a very rich coordination chemistry with potential applications in medicine, materials, and physical sciences. The reaction of Hdihybe with TiCl in methyl alcohol and KOH yielded the tetranuclear titanium oxo-cluster (TOC) [Ti(μ-O)(HOCH)(-Hdihybe)(Hdihybe)]Cl∙10HO∙12CHOH (). The titanium compound was characterized by single-crystal X-ray structure analysis, ESI-MS, C, and H NMR spectroscopy, solid-state and solution UV-Vis, IR vibrational, and luminescence spectroscopies and molecular orbital calculations.

Synthesis, characterization and pharmacological evaluation of quinoline derivatives and their complexes with copper(ΙΙ) in in vitro cell models of Alzheimer's disease.

Alzheimer's disease (AD) is a neurodegenerative disorder of the central nervous system. The main pathophysiological mechanisms involve cholinergic neurotransmission, beta-amyloid (Αβ) and Tau proteins, several metal ions and oxidative stress, among others. Current drugs offer only relief of symptoms and not a cure of AD.

Synthesis, Structural, and Physicochemical Characterization of a Ti and a Unique Type of Zr Oxo Clusters Bearing an Electron-Rich Unsymmetrical {OON} Catecholate/Oxime Ligand and Exhibiting Metalloaromaticity.

The chelating catechol/oxime ligand 2,3-dihydroxybenzaldehyde oxime (Hdihybo) has been used to synthesize one titanium(IV) and two zirconium(IV) compounds that have been characterized by single-crystal X-ray diffraction and H and C NMR, solid-state UV-vis, and ESI-MS spectroscopy. The reaction of TiCl with Hdihybo and KOH in methanol, at ambient temperature, yielded the hexanuclear titanium(IV) compound K[Ti(μ-O)(μ-O)(OCH)(CHOH)(μ-Hdihybo)]·CHOH (), while the reaction of ZrCl with Hdihybo and either BuNOH or KOH also gave the hexanuclear zirconium(IV) compounds and , respectively. Compounds - have the same structural motif [M(μ-Ο)(μ-Ο)] (M = Ti, Zr), which constitutes a unique example with a trigonal-prismatic arrangement of the six zirconium atoms, in marked contrast to the octahedral arrangement of the six zirconium atoms in all the Zr clusters reported thus far, and a unique Zr core structure.

Electrocatalytic hydrogen production by dinuclear cobalt(II) compounds containing redox-active diamidate ligands: a combined experimental and theoretical study.

The chiral dicobalt(ii) complex [CoII2(μ2-L)2] (1) (H2L = N2,N6-di(quinolin-8-yl)pyridine-2,6-dicarboxamide) and its tert-butyl analogue [CoII2(μ2-LBu)2] (2) were synthesized and structurally characterized. Addition of one equivalent of AgSbF6 to the dichloromethane solution of 1 and 2 resulted in the isolation of the mixed-valent dicobalt(iii,ii) species [CoIIICoII(μ2-L)2]SbF6 (3) and [CoIIICoII(μ2-LBu)2]SbF6 (4). Homovalent 1 and 2 exhibited catalytic activity towards proton reduction in the presence of acetic acid (AcOH) as the substrate.

Synthesis, structural and physicochemical characterization of a new type Ti-oxo cluster protected by a cyclic imide dioxime ligand.

Reaction of the cyclic ligand (2Z,6Z)-piperidine-2,6-dione dioxime with TiCl4 and KOH yielded the hexanuclear cluster K6[TiIV6(μ3-O)2(μ2-O)3(CH3O)6(μ2-η1,η1,η2-Hpidiox-O,N,O')4(μ2-η1,η1,η2-pidiox-O,N,O')2]·7.5CH3OH possessing a new {Ti6O5} structural motif. The cluster core {Ti6O5} is wrapped by external tripodal imide dioxime ligands, showing good solubility and stability and thus, allowing its solution to be studied by means of electrospray ionization mass spectrometry, electrochemistry and 2D NMR, c.

Investigation of dioxygen activation by copper(ii)-iminate/aminate complexes.

The activation of dioxygen by metal ions is critical in chemical and bio-chemical processes. A scientific challenge is the elucidation of the activation site of dioxygen in some copper metalloproteins, which is either the metal center or the substrate. In an effort to address this challenge, we prepared a series of new copper(ii) complexes (1·2H2O, 2·CH3OH, 3) with bio-inspired amidate ligands and investigated their activity towards dioxygen activation.

Bis(hydroxylamino)triazines: High Selectivity and Hydrolytic Stability of Hydroxylamine-Based Ligands for Uranyl Compared to Vanadium(V) and Iron(III).

The development of ligands with high selectivity and affinity for uranium is critical in the extraction of uranium from human body, radioactive waste, and seawater. A scientific challenge is the improvement of the selectivity of chelators for uranium over other heavy metals, including iron and vanadium. Flat ligands with hard donor atoms that satisfy the geometric and electronic requirements of the UO exhibit high selectivity for the uranyl moiety.

Design and Assembly of Covalently Functionalised Polyoxofluorovanadate Molecular Hybrids.

Mixed-valent polyoxometalate (POM) clusters are one of the most interesting host species, showing a wide range of structural features and properties. The facile preparation and functionalisation of a mixed-valent polyoxofluorovanadates is reported, where two electrons are trapped to antipodal sites of the clusters. The first members of this family of clusters with the general formula, [V V O (μ-O) (μ -O) (μ -F) (L) ] , where L: py=pyridine (1); pyr=pyrazine (2); im=imidazole (3), are unique organic-inorganic hybrids with the addition of a N-donor ligand at either end of the polyoxofluorovanadate.

Synthesis, Bonding, and Reactivity of Vanadium(IV) Oxido-Fluorido Compounds with Neutral Chelate Ligands of the General Formula cis-[V(IV)(═O)(F)(L(N-N))2](+).

Reaction of the oxidovanadium(IV)-L(N-N) species (L(N-N) is bipy = 2,2'-bipyridine or bipy-like molecules) with either BF4(-) or HF and/or KF results in the formation of compounds of the general formula cis-[V(IV)(═O)(F)(L(N-N))2](+). Structural and spectroscopic (electron paramagnetic resonance) characterization shows that these compounds are in the tetravalent oxidation state containing a terminal fluorido ligand. Density functional theory calculations reveal that the V(IV)-F bond is mainly electrostatic, which is reinforced by reactivity studies that demonstrate the nucleophilicity of the fluoride ligand in a halogen exchange reaction and in fluorination of various organic substrates.

Oxidovanadium(IV/V) complexes as new redox mediators in dye-sensitized solar cells: a combined experimental and theoretical study.

Corrosiveness is one of the main drawbacks of using the iodide/triiodide redox couple in dye-sensitized solar cells (DSSCs). Alternative redox couples including transition metal complexes have been investigated where surprisingly high efficiencies for the conversion of solar to electrical energy have been achieved. In this paper, we examined the development of a DSSC using an electrolyte based on square pyramidal oxidovanadium(IV/V) complexes.

Donor atom electrochemical contribution to redox potentials of square pyramidal vanadyl complexes.

A simple donor atom additivity relationship has been used to calculate the donor atom electrochemical contribution (DEC) of the Oac (acetylacetonate-enolic oxygen), OPh (phenolic oxygen), SPh (mercaptophenol sulfur), Nam (deprotonate amide nitrogen), Nim (imine nitrogen) and Npy (pyridine nitrogen) to the redox processes of the square pyramidal vanadyl complexes. The study focuses on the amidate vanadyl complexes because of (a) their biological interest and (b) the existence of data from plethora complexes studied in great details. The electrochemical contributions for the vanadyl oxidation and reduction processes increase following the same order, OPh~Oac(enolic) View Article and Find Full Text PDF

Interaction of chromium(III) with a N,N'-disubstituted hydroxylamine-(diamido) ligand: a combined experimental and theoretical study.

Reaction of hydroxylamine hydrochloride with prop-2-enamide in dichloromethane in the presence of triethylamine resulted in the isolation of the N,N'-disubstituted hydroxylamine-(diamido) ligand, 3,3'-(hydroxyazanediyl)dipropanamide (Hhydia). The ligand Hhydia was characterized by multinuclear NMR, high-resolution electrospray ionization mass spectrometry (ESI-MS), and X-ray structure analysis. Interaction of Hhydia with trans-[Cr(III)Cl2(H2O)4]Cl·2H2O in ethanol yields the ionization isomers [Cr(III)(Hhydia)2]Cl3·2H2O(1·2H2O) and cis/trans-[Cr(III)Cl2(Hhydia)2]Cl·2H2O (2·2H2O).

Molybdenum(VI) coordination chemistry of the N,N-disubstituted bis(hydroxylamido)-1,3,5-triazine ligand, H2bihyat. Water-assisted activation of the Mo(VI)═O bond and reversible dimerization of cis-[Mo(VI)O2(bihyat)] to [Mo(VI)2O4(bihyat)2(H2O)2].

Reaction of the N,N-disubstituted bis(hydroxylamino) ligand 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine (H(2)bihyat) with cis-[Mo(VI)O(2)(acac)(2)] in tetrahydrofuran resulted in isolation of the mononuclear compound cis-[Mo(VI)O(2)(bihyat)] (1). The treatment of Na(2)Mo(VI)O(4)·2H(2)O with the ligand H(2)bihyat in aqueous solution gave the dinuclear compounds cis-[Mo(VI)(2)O(4)(bihyat)(2)(H(2)O)(2)] (2) and trans-[Mo(VI)(2)O(4)(bihyat)(2)(H(2)O)(2)] (3) at pH values of 3.5 and 5.

Tris-(hydroxyamino)triazines: high-affinity chelating tridentate O,N,O-hydroxylamine ligand for the cis-V(V)O2(+) cation.

The treatment of the trichloro-1,3,5-triazine with N-methylhydroxylamine hydrochloride results in the replacement of the three chlorine atoms of the triazine ring with the function -N(OH)CH(3) yielding the symmetrical tris-(hydroxyamino)triazine ligand H(3)trihyat. Reaction of the ligand H(3)trihyat with NaV(V)O(3) in aqueous solution followed by addition of Ph(4)PCl gave the mononuclear vanadium(V) compound Ph(4)P[V(V)O(2)(Htrihyat)] (1). The structure of compound 1 was determined by X-ray crystallography and indicates that this compound has a distorted square-pyramidal arrangement around vanadium.

Hydrothermal syntheses, crystal structures and physicochemical properties of 2-D and 3-D inorganic coordination cobalt(II)-sulfite polymers.

The hydrothermal reaction of [Co(III)(NH(3))(6)]Cl(3) with Na(2)SO(3) yields, depending on the concentration of Na(2)SO(3), compounds {Na[Co(II)(2)(SO(3))(2)(mu(3)-OH)(H(2)O)]}(infinity) (1) and {Na(4)[Co(II)(2)(SO(3))(4)]}(infinity) (2). When (NH(4))(2)SO(3) x H(2)O was substituted for Na(2)SO(3), the trinuclear mixed valence cobalt(II/III) complex (NH(4))(4){Co(II)[Co(III)(SO(3))(3)(NH(3))(3)](2)} x 2H(2)O (3 x 2H(2)O) was isolated. The cobalt-sulfites 1-3 x 2H(2)O were structurally characterized.

Unexpected synthesis of an unsymmetrical mu-oxido divanadium(V) compound through a reductive cleavage of a N-O bond and cleavage-hydrolysis of a C-N bond of an N,N-disubstituted bis-(hydroxylamino) ligand.

Reaction of the N,N-disubstituted bis-(hydroxylamino) ligand 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine, H(2)bihyat, with V(IV)OSO(4).5H(2)O in water for 6 h followed by the addition of methyl alcohol resulted in the isolation of the unsymmetrical mu-oxido divanadium(V) compound [V(V)(2)O(2)(mu(2)-O)(bihyat)(hyta)(hyto)].3H(2)O (1.

Vanadium(V) compounds with the bis-(hydroxylamino)-1,3,5-triazine ligand, H2bihyat: synthetic, structural, and physical studies of [V2(V)O3(bihyat)2] and of the enhanced hydrolytic stability species cis-[V(V)O2(bihyat)]-.

Reaction of the ligand 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine (H(2)bihyat) with NaV(V)O(3) in aqueous solution followed by addition of either Ph(4)PCl or C(NH(2))(3)Cl, respectively, gave the mononuclear vanadium(V) compounds Ph(4)P[V(V)O(2)(bihyat)].1.5H(2)O (1) and C(NH(2))(3)[V(V)O(2)(bihyat)] (2).