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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 lithium hexamethyldisilazide (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. The aggregation number, the rate constants and the thermodynamic properties of these structural changes were determined by analyzing in detail the concentration-dependent relaxation parameters. The low-frequency relaxation mechanism dominates the acoustic spectra in the high LiHMDS mole fractions, while the high-frequency relaxation influences the spectra in the low LiHMDS mole fractions. In the intermediate mole fraction region (0.25 to 0.46), both relaxations prevail in the spectra. The adiabatic compressibility, the excess adiabatic compressibility and the theoretically estimated mean free length revealed a crossover in the 0.25 to 0.46 LiHMDS mole fractions that signified the transition from one structural mechanism related with the hetero-association of LiHMDS dimers with toluene molecules to the other structural mechanism assigned to the formation of LiHMDS trimers. The combined use of acoustic spectroscopy with theoretical calculations permitted us to disentangle the underlying structural mechanisms and evaluate the volume changes associated with each reaction. The results were compared with the corresponding theoretically predicted volume changes and discussed in the context of the concentration effect on intermolecular bonding. [ABSTRACT FROM AUTHOR]

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. The protonation of HMTA is ruled out due to the large differences between the experimental and the theoretically calculated spectra of the protonated molecules of HTMA in the fingerprint region. In the low-concentration solutions, the hetero-aggregation reaction of HMTA with water is the dominant mechanism, while at higher concentrations, a self-aggregation mechanism occurs. Ultrasonic absorption and velocity measurements were carried out for hexamethylenetetramine aqueous solutions. The acoustic spectra reveal the presence of only one single Debye-type relaxation process that is assigned to the aggregation mechanism of HMTA. The sound absorption data follow two different dependencies on the HMTA mole fraction. The crossover 0.018 mole fraction signifies two separate regions with distinct structural characteristics. The relaxation mechanism observed in dilute solutions was attributed to hetero-association of HMTA with water molecules, while at higher concentrations, the observed relaxation process was assigned to the self-association reaction of HMTA molecules. This structural transformation is also reflected in several physicochemical properties of the system, including the kinematic viscosity, the mass density, the sound speed and the adiabatic compressibility of the HMTA aqueous solutions. The combination of vibrational and acoustic spectroscopies with molecular orbital calculations allowed us to disentangle the underlying processes and to elucidate the observed relaxation mechanism in the HMTA aqueous solutions. [ABSTRACT FROM AUTHOR]

Based on the strong binding properties of hydroxylamino-1,3,5-triazine (BHT) for hard metal ions, a novel spectroscopically labelled triazine-hydroxylaminato ligand, N,N′-(6-(9H-carbazol-9-yl)-1,3,5-triazine-2,4-diyl)bis(N-methylhydroxylamine) (H2cbht), was synthesized. Reaction of H2cbht with FeIII, VV and UVI resulted in the synthesis of [UVIO2(cbht)(DMF)(MeOH)], 1, (PPh4)2([UVIO2(Hcbht)2]·2[UVIO2(Hcbht)(cbht)]), 2, (PPh4)2[(UVIO2)3(μ-cbht)2(cbht)2], 3, Na[VVO2(cbht)], 4, and (PPh4)[FeIII(cbht)2], 5. The complexes were characterized by X-ray crystallography showing strong chelation of the metal ions with the BHT chelating moiety H2cbht. The DMSO/DMF solutions of the complexes were characterized by NMR, UV-vis and electrochemistry, confirming the high affinity of H2cbht for FeIII, VV or UVI. The luminescence properties of the carbazole group were retained in the BHT adduct of the H2cbht ligand. Interaction of the metal ions with H2cbht resulted in quenching of the luminescence of H2cbht. Stern–Volmer plots of luminescence vs. concentration of the metal ions are linear and suitable for the determination of the concentration of metal ions in nM range concentrations. Benesi–Hildebrand plots show that the metal-to-ligand ratio is 1 : 1 while the formation of the metal complexes exhibits high association constants. [ABSTRACT FROM AUTHOR]

Utilizing new experimental approaches and gradual understanding of the underlying chemical processes has led to advances in the self-assembly of inorganic and metal–organic compounds at a very fast pace over the last decades. Exploitation of unveiled information originating from initial experimental observations has sparked the development of new families of compounds with unique structural characteristics and functionalities. The main source of inspiration for numerous research groups originated from the implementation of the design element along with the discovery of new chemical components which can self-assemble into complex structures with wide range of sizes, topologies and functionalities. Not only do self-assembled inorganic and metal–organic chemical systems belong to families of compounds with configurable structures, but also have a vast array of physical properties which reflect the chemical information stored in the various "modular" molecular subunits. The purpose of this short review article is not the exhaustive discussion of the broad field of inorganic and metal–organic chemical systems, but the discussion of some representative examples from each category which demonstrate the implementation of new synthetic approaches and design principles. [ABSTRACT FROM AUTHOR]

Focuses on the synthesis and characterization of vanadium (V) and vanadium (IV) complexes [VOCl3(Hypcan)] and [VOCl2(CH3CN)(Hypcan)]. Vanadium-protein interactions; X-ray structures.

A simple donor atom additivity relationship has been used to calculate the donor atom electrochemical contribution ( DEC ) of the O ac (acetylacetonate-enolic oxygen), O Ph (phenolic oxygen), S Ph (mercaptophenol sulfur), N am (deprotonate amide nitrogen), N im (imine nitrogen) and N py (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, O Ph ~ O ac(enolic) < S Ph ~ N am < N im < N py . These values predict the electrochemical potentials of square pyramidal vanadyl complexes with high accuracy. Octahedral complexes with the same equatorial environment show significant shift of the oxidation potentials to lower values. The DEC influence to the square pyramidal vanadyls' electrochemical potentials has been evaluated. [ABSTRACT FROM AUTHOR]

The hydrolytically stable dioxime ligand (2Z-6Z)-piperidine-2,6-dione (H3pidiox) 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 ZrCl4 with H3pidiox in methanol gives the mononuclear compound [ZrIV(η1,η1,η2-H2pidiox-O,N,O′)2(OH2)2]Cl2·H2O·CH3OH (1), while the same reaction mixture in the presence of KOH gave the pentanuclear ZrOC [Zr IV5 (μ2-OH)4(OH2)4(μ2–η1,η1,η2-Hpidiox-O,N,O′)4(η1,η1,η1-HpidioxO,N,O′)4]·5KCl·3CH3OH·8H2O (2). Compound 1 is formed at very acidic pH = 0, and the pentanuclear ZrOC 2 at higher pH values (pH = 2). Compounds 1 and 2 were characterized by single crystal X-ray structure analysis, multi-nuclear NMR spectroscopy and ESI-MS spectrometry. The single crystal X-ray structure analysis of 1 revealed a mononuclear zirconium(IV) compound containing an eight-coordinate zirconium atom bound to two singly deprotonated H2pidiox− ligands and two water molecules in a severely distorted bicapped octahedral geometry. The pentanuclear ZrOC 2 constitutes the second example of a Zr5 cluster to be reported and the first one in which the four zirconium atoms are arranged in a tetrahedral arrangement with the fifth occupying the center of the tetrahedron. 1D and 2D NMR spectroscopies of the acidic CD3OD solutions of complex 1 reveal a fast equilibrium between 1 and 2. Addition of KOH into a CH3OH solution of 2 results in the controlled fast transformation of 2 to an asymmetric hexanuclear ZrOC 3 as evidenced by the NMR and real-time ESI-MS solution studies. Further addition of KOH to the solution of 3 leads to the ZrOC 4, and on the basis of NMR and ESI-MS data and in comparison with the known hexanuclear titanium(IV)/H3pidiox cluster, it is concluded that the cluster 4 should have a hexanuclear structure. Electrospray ionization mass spectrometry (ESI-MS) demonstrated not only the structural stability 1 and 2 in solution, but also revealed the reversible pH driven dis-assembly/re-assembly process between the monomeric 1 and the pentanuclear ZrOC 2. [ABSTRACT FROM AUTHOR]

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. The complexes are stable in solution while their catalytic turnover frequency is estimated at 10 and 34.6 h−1 molcat−1 for 1 and 2, respectively. Calculations reveal one-electron reduction of 1 is ligand-based, preserving the dicobalt(II) core and activating the ligand toward protonation at the quinoline group. This creates a vacant coordination site that is subsequently protonated to generate the catalytically ubiquitous Co(III) hydride. The dinuclear structure persists throughout where the distal Co(II) ion modulates the reactivity of the adjacent metal site by promoting ligand redox activity through spin state switching. [ABSTRACT FROM AUTHOR]

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. w. EPR and UV-vis spectroscopies. Density Functional Theory (DFT) calculations reveal that the cyclo-Ti3 metallic cores exhibit metallaromaticity which is expected to contribute to the stabilization of this system. [ABSTRACT FROM AUTHOR]

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. The secondary amine group ligated to copper(ii) of the complex 1·2H2O in methyl alcohol is oxidized (2e−) by air dioxygen in a stepwise fashion to an imine group, affording complex 2. The copper(ii) complex 2 in methyl alcohol induces the 4e− oxidation by air dioxygen of the imine functionality ligated to copper(ii) to an azinate group, resulting in the isolation of a dinuclear azinate copper(ii) compound (4). Experimental and computational studies, including X-band c. w. EPR, UV-vis and ESI-MS spectroscopy and density functional theory computations, indicate a direct attack of the dioxygen on the –HC=N– group ligated to copper(ii), and a possible mechanism of the oxidation of the –HC=N– functionality ligated to copper(ii) to an azinate group is provided. This unprecedented activation of dioxygen by a copper substrate paves the way for further exploration of the O2 activation mechanisms in enzymes and the development of effective catalysts in O2-involved green organic synthesis. [ABSTRACT FROM AUTHOR]

Although directly relevant to metal mediated biological nitrification and the coordination chemistry of peroxide, the transition metal complexes of hydroxylamines and their functionalized variants remain mainly unexplored except vanadium(V) and molybdenum(VI). Reaction of the chelating hydroxylamine ligand 3,3′-(hydroxyazanediyl)dipropanamide (Hhydia) with [M II (CH 3 COO) 2 ]· x H 2 O (M = Co II , Zn II ) in methyl alcohol solution yields the complexes [Co II ( η 1 : η 1 -CH 3 COO)( η 1 -CH 3 COO)(Hhydia)], ( 1 ) and [Zn II ( η 1 -CH 3 COO) 2 (Hhydia)], (4 ), while reaction of Hhydia with trans -[Ni II Cl 2 (H 2 O) 4 ]·2H 2 O yields [Ni II (Hhydia) 2 ]Cl 2 ( 3 ). The X-ray structure analysis of 1 and 4 revealed that the Co II and Zn II atoms are bonded to a neutral tridentate O , N , O -Hhydia ligand and a chelate and a monodentate acetate groups in a severely distorted octahedral geometry for 1 and two monodentate acetate groups for 4 in a highly distorted trigonal bipyramidal geometry ( τ  = 0.63). The X-ray structure analysis of 3 revealed that the nickel atom in [Ni II (Hhydia) 2 ] 2+ is bonded to two neutral tridentate O , N , O -Hhydia ligands. The twist angle, θ , in [Ni II (Hhydia) 2 ] 2+ is 55.1(2)°, that is, very close to an ideal octahedron. The metal/Hhydia complexes were studied by UV–Vis (cobalt and nickel compounds), NMR (zinc compounds), HR-MS spectroscopy. The 1 H and 13 C NMR spectra of the methyl alcohol or acetonitrile solutions of Zn II -Hhydia complexes show the existence of both the 1:1 and 1:2 metal:ligand species being in dynamic equilibrium. The exchange processes between the Zn II -Hhydia is through complete dissociation-association of the ligand from the complexes as it is evident from the 2D { 1 H} EXSY NMR spectroscopy. UV–Vis spectroscopy of the Co II -Hhydia in methyl alcohol also shows the existence of both the 1:1 and 1:2 metal:ligand species in contrast to 1:2 complex [Ni II (Hhydia) 2 ] 2+ which is the only species found in solution. The NMR and UV–Vis observations are additionally supported by the HR-MS studies. [ABSTRACT FROM AUTHOR]

Abstract: 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, [VV12VIV2O16(μ‐O)10(μ3‐O)10(μ3‐F)2(L)2]6−, 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. The composition and connectivity of 1–3 were characterised by single‐crystal X‐ray diffraction and electrospray ionisation mass spectrometry. Electron paramagnetic resonance spectroscopy revealed that the two well‐separated VIV ions in each cluster are fully uncoupled with J=0, giving a degenerate singlet–triplet ground state. This attenuation of the exchange interaction is probed with density functional theoretical calculations that reveal that the inclusion of the fluoride ion in the cluster produces a bond pathway biased toward destructive interference between competing ferromagnetic and antiferromagnetic interactions. These robust molecular materials are the ideal combination of desirable electronic properties, with an organic handle with which they can be integrated into spintronic circuitry for molecular devices. [ABSTRACT FROM AUTHOR]

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. The oxidovanadium(IV) complex (Ph4P)2[VIVO(hybeb)] was combined with its oxidized analogue (Ph4P)[VVO(hybeb)] {where hybeb4- is the tetradentate diamidodiphenolate ligand [1-(2-hydroxybenzamido)-2-(2-pyridinecarboxamido)benzenato}and applied as a redox couple in the electrolyte of DSSCs. The complexes exhibit large electron exchange and transfer rates, which are evident from electron paramagnetic resonance spectroscopy and electrochemistry, rendering the oxidovanadium(IV/V) compounds suitable for redox mediators in DSSCs. The very large self-exchange rate constant offered an insight into the mechanism of the exchange reaction most likely mediated through an outer-sphere exchange mechanism. The [VIVO(hybeb)]2-/[VVO(hybeb)]- redox potential and the energy of highest occupied molecular orbital (HOMO) of the sensitizing dye N719 and the HOMO of [VIVO(hybeb)]2- were calculated by means of density functional theory electronic structure calculation methods. The complexes were applied as a new redox mediator in DSSCs, while the cell performance was studied in terms of the concentration of the reduced and oxidized form of the complexes. These studies were performed with the commercial Ru-based sensitizer N719 absorbed on a TiO2 semiconducting film in the DSSC. Maximum energy conversion efficiencies of 2% at simulated solar light (AM 1.5; 1000 W m-2) with an open circuit voltage of 660 mV, a short-circuit current of 5.2 mA cm-2, and a fill factor of 0.58 were recorded without the presence of any additives in the electrolyte. [ABSTRACT FROM AUTHOR]

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-[CrIIICl2(H2O)4]Cl·2H2O in ethanol yields the ionization isomers [CrIII(Hhydia)2]Cl3·2H2O(1·2H2O) and cis/trans-[CrIIICl2(Hhydia)2]Cl·2H2O (2·2H2O). The X-ray structure analysis of 1 revealed that the chromium atom in [CrIII(Hhydia)2](3+) is bonded to two neutral tridentate O,N,O-Hhydia ligands. The twist angle, ?, in [CrIII(Hhydia)2](3+) is 54.5(6)(0), that is, very close to an ideal octahedron. The intramolecular hydrogen bonds developed between the N-OH group of the first ligand and the amidic oxygen atom of the second ligand and vice versa contribute to the overall stability of the cation [CrIII(Hhydia)2]3+. The reaction rate constant of the formation of CrIII complexes 1·2H2O and 2·2H2O was found to be 8.7(±0.8) × 10(-5) M(-1) s(-1) at 25 °C in methyl alcohol and follows a first-order law kinetics based on the biologically relevant ligand Hhydia. The reaction rate constant is considerably faster in comparison with the corresponding water exchange rate constant for the hydrated chromium(III). The modification of the kinetics is of fundamental importance for the chromium(III) chemistry in biological systems. Ultraviolet-visible and electron paramagnetic resonance studies, both in solution and in the solid state, ESI-MS, and conductivity measurements support the fact that, irrespective of the solvent used in the interaction of Hhydia with trans-[CrIIICl2(H2O)4]Cl·2H2O, the ionization isomers[CrIII(Hhydia)2]Cl3·2H2O (1·2H2O) and cis/trans-[CrIIICl2(Hhydia)2]Cl·2H2O (2·2H2O) are produced. The reaction medium affects only the relevant percentage of the isomers in the solid state. The thermodynamic stability of the ionization isomers 1·2H2O and cis/trans-2·2H2O, their molecular structures as well as the vibrational spectra and the energetics of the CrIII- Hhydia/hydia(-) were studied by means of density functional theory calculations and found to be in excellent agreement with our experimental observations. [ABSTRACT FROM AUTHOR]

Polyoxometalates (POMs) are anionic metal oxides and encompass a diverse family of nanosized compounds with an unmatched range of architectures and physical properties. The use of the pyramidal sulfite anion, with its numerous coordination modes, has introduced structural diversity into the POM-based chemical systems, giving rise to the formation of novel synthons for the construction of unprecedented architectures ranging from low-nuclearity, isolable secondary building units to POM-based molecular nanoparticles, open-framework and 3D coordination materials, and the emergence of novel properties. [ABSTRACT FROM AUTHOR]

Reaction of the N,N-disubstituted bis(hydroxylamino) ligand 2,6-bis[hydroxy(methyl)amino]-4-morpholino-l,3,5-triazine (H2bihyat) with eis-[MoVI 02(acac)2] in tetrahydrofuran resulted in isolation of the mononuclear compound cis-[MoVI02(bihyat)] (l). The treatment of Na2Mo2VI04-2H20 with the ligand H2bihyat in aqueous solution gave the dinuclear compounds cis-[Mo2VI04(bihyat)2(H20)2] (2) and trans-[Mo2VI04(bihyat)2(H20)2] (3) at'pH values of 3.5 and 5.5, respectively. The structures for the three molybdenum (VI) compounds were determined by X-ray crystallography. Compound 1 has a square-pyramidal arrangement around molybdenum, while in the two dinuclear compounds, each molybdenum atom is in a distorted pentagonal-bipyramidal environment of two bridging and one terminal oxido groups, a tridentate (0,N,0) bihyat2- ligand that forms two five-membered chelate rings, and a water molecule trans to the terminal oxido group. The dinuclear compounds constitute rare examples containing the {Mo2VI02(μ2-02)}4+ moiety. The potentiometry revealed that the MoVIbihyat2- species exhibit high hydrolytic stability in aqueous solution at a narrow range of pH values, 3--5. A subtle change in the coordination environment of the five-coordinate compound 1 with ligation of a weakly bound water molecule trans to the oxido ligand ( lw) renders the equatorial oxido group in 1 w more nucleophilic than that in 1, and this oxido group attacks a molybdenum atom and thus the dinuclear compounds 2 and 3 are formed. This process might be considered as the first step of the oxido group nucleophilic attack on organic substrates, resulting in oxidation of the substrate, in the active site of molybdenum enzymes such as xanthine oxidase. Theoretical calculations in the gas phase were performed to examine the influence of water on the dimerization process (l→2/3). In addition, the molecular structures, cis/trans geometrical isomerism for the dinuclear molybdenum(VI) species, vibrational spectra, and energetics of the metal--ligand interaction for the three molybdenum(Vl) compounds 1--3 have been studied by means of density functional theory calculations. [ABSTRACT FROM AUTHOR]

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)CH3yielding the symmetrical tris-(hydroxyamino)triazine ligand H3trihyat. Reaction of the ligand H3trihyat with NaVVO3in aqueous solution followed by addition of Ph4PCl gave the mononuclear vanadium(v) compound Ph4P[VVO2(Htrihyat)] (1). The structure of compound 1was determined by X-ray crystallography and indicates that this compound has a distorted square-pyramidal arrangement around vanadium. The ligand Htrihyat2−is bonded to vanadium atom in a tridentate fashion at the triazine ring nitrogen atom and the two deprotonated hydroxylamido oxygen atoms. The high electron density of the triazine ring nitrogen atoms, which results from the resonative contribution of electrons of exocyclic nitrogen atoms, leads to a very strong V–N bond. The cis-[VVO2(Htrihyat)]−species exhibits high hydrolytic stability in aqueous solution over a wide pH range, 2.5–11.5, as was evidenced by potentiometry. [ABSTRACT FROM AUTHOR]

The hydrothermal reaction of [CoIII(NH3)6]Cl3with Na2SO3yields, depending on the concentration of Na2SO3, compounds {Na[CoII2(SO3)2(μ3-OH)(H2O)]}∞(1) and {Na4[CoII2(SO3)4]}∞(2). When (NH4)2SO3·H2O was substituted for Na2SO3, the trinuclear mixed valence cobalt(ii/iii) complex (NH4)4{CoII[CoIII(SO3)3(NH3)3]2}·2H2O (3·2H2O) was isolated. The cobalt-sulfites 1–3·2H2O were structurally characterized. In 1, the 1-D chains along the a-axis of the subunit [CoII(2)CoII(3)(OH)2(SO3)2] are cross-linked with CoII(1) atoms viaCo–Osulfiteand Co–Ohydroxidebonds in 2-D sheets, that are further stacked through interlayer hydrogen bonds. In 2, the [CoII2(SO3)2]∞chains along the b-axis are cross-linked with tetrahedral cobalts viaCoII–Osulfitebonds in 2-D sheets parallel to the ab-plane and the sheets are further bound to sodium atoms viaNa–Osulfitebonds to form a 3-D structure. The 3-D inorganic coordination polymer, 2, crystallizes in the non-centrosymmetric space group P212121. In addition, in compound 2octahedral and tetrahedral cobalt atoms coexist, which is rather unusual for cobalt clusters. Compound 3·2H2O is a 0-D mixed-valence {[(NH3)3CoIII(μ-SO3)3]CoII[(μ-SO3)3CoIII(NH3)3]}4−trinuclear cluster and can be considered as an octahedral {CoIIO6} complex ligated to two tridentate [(NH3)3CoIII(SO3)3]3−ligands. The trinuclear clusters are stacked through an extended network of hydrogen bonding into a 3-D structure. Variable temperature magnetic susceptibility studies for 1–3·2H2O revealed that 1and 2are 2-D magnetic systems with strong antiferromagnetic interaction between the CoIIatoms leading to an S= 0 ground state for 1, while in compound 2there is an almost zero interaction between the cobalt(ii) atoms leading to a non-zero ground state. The trinuclear compound 3·2H2O has two diamagnetic CoIIIatoms and a high-spin CoIIatom with D= 84(1) cm−1, E= 6(1) cm−1and g= 2.56(1). The IR, the solid-state UV-vis spectra and the thermogravimetric analyses of compounds 1–3·2H2O are also reported. [ABSTRACT FROM AUTHOR]

The hydrothermal reaction of [CoIII(NH3)6]Cl3with Na2SO3yields, depending on the concentration of Na2SO3, compounds {Na[CoII2(SO3)2(μ3-OH)(H2O)]}∞(1) and {Na4[CoII2(SO3)4]}∞(2). When (NH4)2SO3·H2O was substituted for Na2SO3, the trinuclear mixed valence cobalt(ii/iii) complex (NH4)4{CoII[CoIII(SO3)3(NH3)3]2}·2H2O (3·2H2O) was isolated. The cobalt-sulfites 1–3·2H2O were structurally characterized. In 1, the 1-D chains along the a-axis of the subunit [CoII(2)CoII(3)(OH)2(SO3)2] are cross-linked with CoII(1) atoms viaCo–Osulfiteand Co–Ohydroxidebonds in 2-D sheets, that are further stacked through interlayer hydrogen bonds. In 2, the [CoII2(SO3)2]∞chains along the b-axis are cross-linked with tetrahedral cobalts viaCoII–Osulfitebonds in 2-D sheets parallel to the ab-plane and the sheets are further bound to sodium atoms viaNa+–Osulfitebonds to form a 3-D structure. The 3-D inorganic coordination polymer, 2, crystallizes in the non-centrosymmetric space group P212121. In addition, in compound 2octahedral and tetrahedral cobalt atoms coexist, which is rather unusual for cobalt clusters. Compound 3·2H2O is a 0-D mixed-valence {[(NH3)3CoIII(μ-SO3)3]CoII[(μ-SO3)3CoIII(NH3)3]}4−trinuclear cluster and can be considered as an octahedral {CoIIO6} complex ligated to two tridentate [(NH3)3CoIII(SO3)3]3−ligands. The trinuclear clusters are stacked through an extended network of hydrogen bonding into a 3-D structure. Variable temperature magnetic susceptibility studies for 1–3·2H2O revealed that 1and 2are 2-D magnetic systems with strong antiferromagnetic interaction between the CoIIatoms leading to an S= 0 ground state for 1, while in compound 2there is an almost zero interaction between the cobalt(ii) atoms leading to a non-zero ground state. The trinuclear compound 3·2H2O has two diamagnetic CoIIIatoms and a high-spin CoIIatom with D= 84(1) cm−1, E= 6(1) cm−1and g= 2.56(1). The IR, the solid-state UV-vis spectra and the thermogravimetric analyses of compounds 1–3·2H2O are also reported. [ABSTRACT FROM AUTHOR]

Reaction of the N,N-disubstituted bis-(hydroritamino) ligand 2,6-bis[hydroxy(methyt)aminoj-4-motpholino-1,3,5-triazine, H2bihyat, with VIVOSO4 ∙ 5H2O in water for 6 h followed by the addition of methyl alcohol resulted in the isolation of the unsymmetrical μ-oxido divanadium(V) compound [VV2O2(μ2-O)(bihyal)(hyta)(hyto)]∙3H2O (1 ∙ 3H2O) and of the methythydroxylamido derivative [VVO(bihyat)(CH3NHO)] ∙ H2O (2 ∙ H2O). The N,N-disubstituted mono(hydrosyiamino) ligands Hhyta, Hhyto, and CH3NHOH were formed by the decomposition of the ligand H2bihyat in the presence of vanadium. The structures of compounds 1 ∙ 3H2O and 2 ∙ H2O were determined by X-ray crystallography. The structure of 1 ∙ 3H2O consists of one five-coordinate vanadium(V) atom and one six-coordinate vanadium(V) atom bridged by an otddo group and ligated to a tridentate bihyat and two bidentate hyta and hyto ligands, respectively. The two terminal oxido groups in 1 ∙ 3H2O are syn-directed, lying on the same side of the V-O-V plane. The coordination environment of the vanadium atom in 2 ∙ H2O approximates to a highly distorted pentagonal pyramid with the oxido ligand occupying the apical position. Compounds 1 ∙ 3H2O and 2 ∙ H2O were studied by multinuclear NMR (1H, 13C, and 51V) to elucidate their solution structures. The 51V NMR of 1 ∙ 3H2O in anhydrous CD2CI2 gave two signals at -199 and -508 ppm, which were assigned to the five- and six-coordinate vanadium(V) atoms, respectively. The resonance of the five-coordinate vanadium nucleus, in a field much lower than that expected from Rehders [lnorg. Chem., 1988, 27, 584-587] referencing scale, was attributed to the low-energy ligand-to-metal charge transfer transition at 605 nm [ϵM=5050 M-1 cm-1] of 1 ∙ 3H2O according to Pecoraro et al. [J. Am. Chem. Soc., 1992, 114, 9925-9933]. Electrospray ionization-mass spectrometry studies were used to follow the decomposition products of H2bihyat in the presence of vanadium. [ABSTRACT FROM AUTHOR]

Reaction of the oxidovanadium(IV)-LN-N species (LN-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-[VIV(═O)(F)(LN-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 VIV-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. [ABSTRACT FROM AUTHOR]

Reaction of Na2MoVIO4·2H2O with (NH4)2SO3 in the mixed-solvent system H2O/CH3CN (pH = 5) resulted in the formation of the tetranuclear cluster (NH4)4[Mo4VISO16]·H2O (1), while the same reaction in acidic aqueous solution (pH = 5) yielded (NH4)4[Mo5VIS2O21]·3H2O (2). Compound {(H2bipy)2[Mo5VIS2O21]·H2O}x (3) was obtained from the reaction of aqueous acidic solution of Na2MoVIO4·2H2O with (NH4)2SO3 (pH = 2.5) and 4,4′-bipyridine (4,4′-bipy). The mixed metal/sulfite species (NH4)7[CoIII(Mo2VO4)(NH3)(SO3)6]·4H2O (4) was synthesized by reacting Na2MoVIO4·2H2O with CoCl2·6H2O and (NH4)2SO3 with precise control of pH (5.3) through a redox reaction. The X-ray crystal structures of compounds 1, 2, and 4 were determined. The structure of compound 1 consists of a ring of four alternately face- and edge-sharing MoVIO6 octahedra capped by the trigonal pyramidal sulfite anion, while at the base of the Mo4 ring is an oxo group which is asymmetrically shared by all four molybdenum atoms. Compound 3 is based on the Strandberg-type heteropolyion [Mo5VIS2O21]4-, and these coordinatively saturated clusters are joined by diprotonated 4,4′-H2bipy2+ through strong hydrogen bonds. Compound 3 crystallizes in the chiral space group C2. The structure of compound 4 consists of a novel trinuclear [CoIIIMo2VSO32- cluster. The chiral compound 3 exhibits nonlinear optical (NLO) and photoluminescence properties. The assignment of the sulfite bands in the IR spectrum of 4 has been carried out by density functional calculations. The cobalt in 4 is a d6 octahedral low-spin metal atom as it was evidenced by magnetic susceptibility measurements, cw EPR, BVS, and DFT calculations. The IR and solid-state UV-vis spectra as well as the thermogravimetric analyses of compounds 1-4 are also reported. [ABSTRACT FROM AUTHOR]

Abstract: The organically templated compound (NH4)3(4,4′-Hbpy)[(VIVO)6(μ 4-O)2(μ 3-OH)2(μ 3-SO3)4(μ-SO3)]·15/2 H2O 1 is the first example of an extended structure in which a polyoxometalate anion, [H2V6 IVS4 IVO22]2–, is linked by the pyramidal μ 2-bridging sulfite group forming a linear polymeric {V6}η chain. Two such chains are linked into a ‘double-rung ladder’ assembly via two different hydrogen bonds provided by 4,4′-Hbpy+ cations. To cite this article: H.N. Miras et al., C. R. Chimie 8 (2005). [Copyright &y& Elsevier]

Reaction of one equivalent of vanadium(III) chloride with three equivalents of l-cysteine(H2Cys) in methyl alcohol affords a VIII-Cys compound that is formulated as [VIII(Hcys)3] · 2HCl · 2.5H2O 1. The solid state characterization of 1 was performed by microanalysis, circular dichroism (CD) and infrared studies as well as room temperature magnetic susceptibility. These studies have shown coordination of each HCys- ligand to the VIII atom through an amine nitrogen and a carboxylate oxygen atoms. Solution studies of 1 were carried out in water and methanol by UV–visible, CD and electron paramagnetic resonance (EPR) spectroscopies. According to these studies, it was evident that despite the progressive oxidation of 1 to oxovanadium(IV) species, some V(III) species were also present in solution after several hours. Compound 1, VIVOSO4 · 5H2O and l-cysteine were examined for their total antioxidant capacity (TAC) and lag time. Compound 1 exhibited significantly greater total antioxidant capacity and lag time values than l-cysteine. VIVOSO4 · 5H2O did not show any total antioxidant capacity or lag time. The inhibition of neutral endopeptidase (NEP) activity caused by 1, VIVOSO4 · 5H2O and thiorphan was also measured. Compound 1, at a concentration of 10-3 M, showed inhibition of NEP activity as potent as thiorphan at 10-6 M, while VIVOSO4 · 5H2O in the same concentration exhibited less than 50% inhibitory activity than that of thiorphan at 10-6 M. Moreover, the antimetastatic effects of compound 1, l-cysteine and VIVOSO4 · 5H2O were examined on Wistar rats, treated with 3,4-benzopyrene. The results revealed that 1 prevents significantly lung metastases (only 9.5% of animals treated with 1 showed metastases), whereas 47–52% of the rats of the control group and those treated with l-cysteine and VIVOSO4 · 5H2O exhibited metastases. [Copyright &y& Elsevier]

Studies the monomeric oxovanadium(IV) compounds. Formulation of the general formula from the reaction of [V[supIV]OCL[sub2](THF)[sub2]] in aqueous solution with AgBF[sub4]; Yield of the addition of Bs(CIO[sub4]) and bipy to an aqueous solution; Demonstration of crystal structures by x-ray diffraction analysis; Crystallization of compound 2.1 in the orthorhombic space group and compound 6 in the monoclinic space group.

Reaction of the non-oxo V[sup IV] species [V[sup IV]Cl[sub 2](L[sub OO])[sub 2][L[sub OO] = acetylacetonate (acac[sup -]) or benzoylacetonate (bzac[sup -])] with a chelate nitrogen-donor ligand L[sub NN] in acetonitrile leads to the reduction of V[sup IV] to V[sup III] and the formation of the mononuclear V[sup III] compounds of the general formula [V[sup III]Cl[sub 2](L[sub OO])(L[sub NN])](L[sup OO] and L[sub NN] are acac[sup -] and bipy for 1; acacand 5,5'-me[sub 2]bipy for 2; acac[sup -] and 4,4'-tb[sub 2]bipy for 3; acac[sup -] and phen for 4; bzac[sup -] and bipy for 5; bzac[sup -] and phen for 6). The reduction of the V[sup IV] complexes was monitored by GC-MS and ¹H NMR spectroscopy. Both one- and two-dimensional (2D COSY and 2D EXSY) ¹H NMR techniques were used to assign the observed ¹H NMR resonances of 1-6 in CD[sub 2]Cl[sub 2] or CDCl[sub 3] solution. It appeared that in solution these V[sup III] complexes form two isomers which are in equilibrium: cis-[V[sup III]Cl[sub 2](L[sub OO])(L[sub NN])] &lrarr; trans-[V[sup III]Cl[sub 2](L[sub OO])(L[sub NN])]. 2D EXSY cross-peaks were clearly observed between bipy- and acac-hydrogen atoms of the two geometrical isomers of 1-3 as well as between bipy and acac[sup -] protons of the cis isomer, indicating a dynamic process that corresponds to cis-trans isomerization and a cis-cis racemization. The thermodynamic and kinetic parameters of the equilibrium between these two isomers were calculated for compounds 1 and 2 by using variable temperature (VT) NMR data. Both cis-trans isomerization and cis-cis racemization processes probably proceed with an intramolecular twist mechanism involving a trigonal prismatic transition state. Density functional calculations (DFT) also indicated such a rearrangement mechanism. [ABSTRACT FROM AUTHOR]

The siderophore organic ligand N,2-dihydroxybenzamide (H2dihybe) 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 H2dihybe with TiCl4 in methyl alcohol and KOH yielded the tetranuclear titanium oxo-cluster (TOC) [TiIV4(μ-O)2(HOCH3)4(μ-Hdihybe)4(Hdihybe)4]Cl4∙10H2O∙12CH3OH (1). The titanium compound was characterized by single-crystal X-ray structure analysis, ESI-MS, 13C, and 1H NMR spectroscopy, solid-state and solution UV–Vis, IR vibrational, and luminescence spectroscopies and molecular orbital calculations. The inorganic core Ti4(μ-O)2 of 1 constitutes a rare structural motif for discrete TiIV4 oxo-clusters. High-resolution ESI-MS studies of 1 in methyl alcohol revealed the presence of isotopic distribution patterns which can be attributed to the tetranuclear clusters containing the inorganic core {Ti4(μ-O)2}. Solid-state IR spectroscopy of 1 showed the presence of an intense band at ~800 cm−1 which is absent in the spectrum of the H2dihybe and was attributed to the high-energy ν(Ti2–μ-O) stretching mode. The ν(C=O) in 1 is red-shifted by ~10 cm−1, while the ν(N-O) is blue-shifted by ~20 cm−1 in comparison to H2dihybe. Density Functional Theory (DFT) calculations reveal that in the experimental and theoretically predicted IR absorbance spectra of the ligand and Ti-complex, the main bands observed in the experimental spectra are also present in the calculated spectra supporting the proposed structural model. 1H and 13C NMR solution (CD3OD) studies of 1 reveal that it retains its integrity in CD3OD. The observed NMR changes upon addition of base to a CD3OD solution of 1, are due to an acid–base equilibrium and not a change in the TiIV coordination environment while the decrease in the complex's lability is due to the improved electron-donating properties which arise from the ligand deprotonation. Luminescence spectroscopic studies of 1 in solution reveal a dual narrow luminescence at different excitation wavelengths. The TOC 1 exhibits a band-gap of 1.98 eV which renders it a promising candidate for photocatalytic investigations. [ABSTRACT FROM AUTHOR]

The first mononuclear MnII complexes with a new N5 tripodal-amidate ligand of the general formula [MnIIN5 trip X] are reported. CV examination of them showed an unexpected two electron oxidation of MnII to MnIV and their OER revealed that the oxidized ligand is responsible for the electrocatalytic oxidation of H 2 O to O 2. [Display omitted] Water oxidation plays a crucial role in both natural and artificial photosynthesis, which is an attractive solution to the depletion of fossil fuels as energy sources due to the increasing consumption. Thus, the search for oxygen evolution reaction catalysts is a hot topic of research. Reaction of the N5-tripodal amidate ligand, N -{2-[(bis(pyridine-2-ylmethyl)amino)methyl]phenyl}picolinamide (Htrip) with MIIX 2 (X = Cl-, Br-, I-), in anhydrous ethyl alcohol, and C 2 H 5 ONa yields the complexes [MnII(trip)Cl] (1), [MnII(trip)Br] (2), and [MnII(trip)I] (3). Single crystal X-ray structure analysis of 1 – 3 revealed that the manganese(II) atom in the three manganese compounds occupies the center of a distorted octahedral coordination sphere consisting of two pyridine, one picoline and one amino nitrogen atoms on the equatorial plane, while the axial positions are occupied by one amido nitrogen atom and the halogen anion. The three manganese(II) complexes 1 – 3 constitute the first examples of mononuclear {MnII(N5 trip)X} species to be reported. Magnetic susceptibility measurements showed that these complexes are high-spin d 5 systems. Cyclic voltametric study of 1 – 3 revealed an unexpected two electron, electrochemically reversible redox process, assigned to the oxidation of MnII to MnIV. The electrochemical properties for oxygen evolution reaction of complexes 1 – 3 showed that the oxidized trip- ligand is responsible for the electrocatalytic oxidation of water to dioxygen. [ABSTRACT FROM AUTHOR]

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. Accumulating evidence suggests that multifunctional compounds, targeting multiple pathophysiological mechanisms, may have a great potential for the treatment of AD. In this study, we report on the synthesis and physicochemical characterization of four quinoline-based metal chelators and their respective copper(II) complexes. Most compounds were non-toxic at concentrations ≤5 μM. In neuroprotection studies employing undifferentiated and differentiated SH-SY5Y cells, the metal chelator N 2, N 6-di(quinolin-8-yl)pyridine-2,6-dicarboxamide (H 2 dqpyca) appeared to exert significant neuroprotection against both, Aβ peptide- and H 2 O 2 -induced toxicities. The copper(II) complex [CuII(H 2 bqch)Cl 2 .3H 2 O (H 2 bqch = N , N ′-Bis(8-quinolyl)cyclohexane-1,2-diamine) also protected against H 2 O 2 -induced toxicity, with a half-maximal effective concentration of 80 nM. Molecular docking simulations, using the crystal structure of the acetylcholinesterase (AChE)-rivastigmine complex as a template, indicated a strong interaction of the metal chelator H 2 dqpyca, followed by H 2 bqch, with both the peripheral anionic site and the catalytic active site of AChE. In conclusion, the sufficient neuroprotection provided by the metal chelator H 2 dqpyca and the copper(II) complex [CuII(H 2 bqch)Cl 2 .3H 2 O along with the evidence for interaction between H 2 dqpyca and AChE, indicate that these compounds have the potential and should be further investigated in the framework of preclinical studies employing animal models of AD as candidate multifunctional lead compounds for the treatment of the disease. Four quinoline derivatives and their copper(II) complexes were synthesized, characterized and evaluated as multifunctional anti-Alzheimer's disease compounds. N 2, N 6-di(quinolin-8-yl)pyridine-2,6-dicarboxamide (H 2 dqpyca) and N , N '-Bis(8-quinolyl)cyclohexane-1,2-diamine](dichlorido)copper(II) ([CuII(H 2 bqch)Cl 2 .3H 2 O) showed neuroprotection against amyloid-β (Aβ) peptide- and/or H 2 O 2 -induced toxicities. Also, H 2 dqpyca strongly interacts with acetylcholinesterase indicating a great potential for multifunctionality. [Display omitted] • Multifunctional compounds are promising agents for treatment of Alzheimer's disease (AD). • Four quinoline derivatives and their copper(II) complexes were characterized. • A diquinoline/pyridine-based agent protects from amyloid-β and H 2 O 2 cellular toxicity. • A bisquinoline/cyclohexane-based copper(II) complex protects from H 2 O 2 cellular toxicity. • We identified two novel compounds as promising multifunctional agents for AD. [ABSTRACT FROM AUTHOR]

Partial oxidation of an aqueous solution of CoIICl2 · 6H2O with (NH4)6[Mo7VIO24] · 4H2O in the presence of (NH4)2SO3 · H2O and LiCI, at pH ≈ 5.3, leads to isolation of the octanuclear cluster (NH4)11(Li⊂[Co4IICo4III(SO3)16(NH3)8] · 10H2O), 1. The structure of the anion of 1 consists of a central [Co4II], almost ideal square planar unit, and a pair of symmetry-related CoIII dimers above and below the Co4II plane grafting onto the tetramer by 16 bridging sulfite groups. The [Co8(SO3)16(NH3)8]12- cluster encapsulates a lithium cation which lies at the center of the Co4II square. [ABSTRACT FROM AUTHOR]

Review: ≈50 refs. [ABSTRACT FROM AUTHOR]