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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]

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]

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]

Novel vanadium(III) and oxovanadium(IV) compounds with the diamidate ligand 1,2-bis(s-pyridinecarboxamide)benzene (H2bpb) were synthesized and structurally and physicochemically characterized. H2bpb is a structurally a very versatile ligand, capable of supporting a wide variety of complex stoichiometries and geometries.

The mixed-valence MnIIIMnII complexes and a homo-valence MnII trinuclear manganese complex of the general composition MnIIIMnIIMnIII(5-Cl-Hsaladhp)2(AcO)4(MeOH)2.4CH3OH, MnIIIMnIIMnIII (Hsaladhp)2(AcO)2(5-Cl-Sal)2-(thf)2, and MnIIMnIIMnII (AcO)6(pybim)2, where H3saladhp = tridentate Schiff base ligand and pybin = neutral bidentate donor ligand, are subjected to structural, solid and solution analyses. The complexes have 18O degrees MnIII-MnII-MnIII angles and are valence trapped with two terminal MnIII ions exhibiting Jahn-Teller distortion.

The interaction of vanadium in oxidation states III, IV, and V with the deprotonated amide(peptide) functionality is described. The results showed that vanadium in these biologically accessible oxidation states form strong bonds with the deprotonated amide nitrogens of the amide group. The results proved that V-Namide binding is a possible mode of action in proteins.

The complexes N-(2- 4-oxopent-2-en-2-ylamino phenyl)pyridine-2-carboxamido oxovanadium(IV) (VO pycac) and N-(2- 4-phenyl-4-oxobut-2-en-2-ylamino phenyl)pyridine-2-carboxamido-oxovanadium(IV) (VO pycbac) were prepared via ligand substitution. The bond lengths and angles of the structures were found to be almost identical. The structure of VO(pycbac) consists of a square pyramidal coordination geometry about the vanadium atom. The oxo ligand occupies the apical position and the donor atoms of the tetradentate ligand occupy the basal plane.

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]

The synthesis, structural and physicochemical characterization of the octanuclear mixed-valence 4[Co.sup.II],4[Co.sup.III]-S[O.sub.3.sup.2-] cluster, [(N[H.sub.4]).sub.11](Li[C][[Co.sub.4.sup.II][Co.sub.4.sup.III][(S[O.sub.3]).sub.16]*[(N[H.sub.3]).sub.8]])*10[H.sub.2]O is reported. The anion of the cluster consists of a central [Co.sub.4.sup.II], almost ideal square planar unit, and a pair of symmetry-related [Co.sup.III] dimers above and below the [Co.sub.4.sup.II] plane.

The synthesis and structural and physicochemical properties of the heteropolyoxomolybdenum(V/VI)-sulfite clusters are presented. The infrared (IR) and solid-state ultraviolet visible (UV-vis) spectra are reported along with the thermogravimetric analyses of compounds.

The versatility of ESE-ENDOR in measuring both metal-center nuclear spin transitions and the effects of axial ligand interactions that are weak and unresolved by CW-EPR spectroscopy is described. The complementary use of DFT and pulsed-ENDOR is dca promising methodology for the study of biologically relevant vanadyl compounds.

The synthesis of two series of monomeric oxovanadium(IV) compounds containing bipy or substituted bipy (LNN), of general formulas cis-[V(super IV)OX(LNN)2](super +/0) (X=OH(super -1), SO4(super 2-), Cl(super -1) and cis-[V(super IV)OY-(LNN)2]Y (Y=BF4(super -1), SbF6(super -1), is reported. Electronic and molecular structures of these two compounds are studied in detail.

Research has been conducted on non-oxo V (super)IV species. The authors report that the reaction of the species with a chelate nitrogen-donor ligand in acetonitrile leads to the reduction of V (super)IV to V (super)III and to the formation of the mononuclear V (super)III compounds.

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]

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]

X-ray crystallographic studies of vanadium(III)- and vanadium(IV/V)-amide interactions reveal that the resulting complexes have a V-O(sub amide) coordination. The complexes are sensitive to air and stable in solution under inert conditions. Cyclic voltammetric studies reveal that the complexes undergo reversible and irreversible redox processes.

The synthesis and structural characterization of a family of vanadium(III) and oxovanadium(IV/V) complexes with the ligands, N-(2-nitrophenyl)pyridine-2-carboxamide, N-(phenyl)pyridine-2-carboxamide and N-(2-pyridyl)acetamide, were described. The compounds were prepared and characterized both in solid state and in solution. The optical, magnetic and infrared characteristics of the compounds were also investigated. All the vanadium compounds consist of a vanadium-amide oxygen bond.

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]

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 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]