Mixed salts containing croconate violet, lanthanide and potassium ions: Crystal structures and spectroscopic characterization of supramolecular compounds

The vibrational spectra and crystal structures of four lanthanide and potassium salts of 3,5-bis(dicyanomethylene)cyclopentane-1,2,4-trionate (), known as croconate violet (CV), are described in this work. All LnKC₂₂N₈O₆ (Ln = La⁺³, Nd⁺³, Gd⁺³ and Ho⁺³) compounds are isostructural, crystallizing in the triclinic space group. In each compound the lanthanide ion is acting as both monodentate and chelate metal sites, whereas the potassium presents only monodentate coordination. The crystal structure shows the formation of a periodic 2D structure extended by K-N bonds parallel to the crystallographic [0 0 1] direction; these 2D sheets form hydrogen bonds with water molecules giving rise to a 3D extended arrangement. It is not possible to observe any type of π-interaction and the main forces responsible to stabilize the structures are the hydrogen bonds. The vibrational spectra of all the compounds are very similar, and the most important vibrational markers for the croconate violet ion, namely the ν(CN) and ν(CO) modes, behave differently: the ν(CN) modes are not shifted by the presence of the lanthanide ion species, only showing small band intensity differences, whereas the ν(CO) bands are shifted to higher wavenumbers, due to their coordination to the metal sites.     

Oxalate, squarate and croconate complexes with bis(2-pyrimidylcarbonyl)amidatecopper(II): synthesis, crystal structures and magnetic properties

The preparation and magnetic properties of three copper(II) compounds of formulae [Cu₂(bpcam)₂(H₂O)₂(C₂O₄)] (1), [Cu₂(bpcam)₂(H₂O)₄(C₄O₄)] · 10 H₂O (2) and Cu₂(bpcam)₂(C₅O₅)(H₂O)₃ (3) [bpcam = bis(2-pyrimidyl)amidate, and are reported. The structures of two of them (1 and 2) have been solved by single crystal X-ray diffraction and consists of centrosymmetric discrete copper(II) dinuclear units bridged by bis-bidentate oxalate (1) and bis-monodentate squarate (2), with the bpcam group acting as a terminal tridentate ligand. Each copper atom in 1 exhibits a distorted elongated octahedral coordination geometry. Three bpcam nitrogen atoms and one oxalate oxygen define the basal plane while the other oxalate oxygen and a water molecule take up the axial positions. Each copper atom in 2 is in an elongated octahedral surrounding with three bpcam nitrogen atoms and one squarate oxygen in the equatorial plane and two water molecules in the axial positions. The intramolecular copper-copper separations are 5.677(1) (1) and 7.819(53) Å (2). Magnetic susceptibility measurements for 1-3 in the temperature range 1.9-290 K show the occurrence of weak ferromagnetic interactions through oxalato (J = +0.75 cm⁻¹) and squarato (J = +1.26 cm⁻¹), the Hamiltonian being defined by . These values are analyzed and discussed in the light of the available magneto-structural data for analogous systems. The quasi-Curie law observed in 3 (θ = −1.15 K) contrasts with the significant antiferromagnetic interaction through bis-chelating croconate in other structurally characterized croconate-bridged copper(II) complexes and rules out the presence of bridging croconate in this compound.     

Manganese(II) complexes with croconate and 2-(2-pyridyl)imidazole ligands: Syntheses, X-ray structures and magnetic properties

The mixed-ligand complexes of manganese(II) of formula [Mn(pyim)₂(C₅O₅)] (1) and [Mn(pyim)(H₂O)(C₅O₅)]_n · 2.5nH₂O (2) [pyim = 2-(2-pyridyl)imidazole and  = croconate (dianion of 4,5-dihydroxy-4-cyclopentene-1,2,3-trione)] have been prepared and their structures determined by X-ray crystallographic methods. Compound 1 is a tris-chelated mononuclear complex where the manganese atom is six-coordinate: four nitrogen atoms from two pyim molecules and two oxygen atoms from a croconate group build a somewhat distorted octahedral surrounding around the metal atom. The resulting neutral mononuclear units are linked to each other through double bridges which are constituted by the imidazole N-H and the metal-coordinated croconate-oxygen atom, the metal-metal separation through this supramolecular pathway being 7.6856(11) Å. Compound 2 is a croconato-bridged manganese(II) uniform chain with an intrachain metal-metal distance of 7.5118(9) Å. A bidentate pyim group, a water molecule and four oxygen atoms from two bis-bidentate croconate ligands build an irregular seven-coordination polyhedron around each manganese atom in 2. The investigation of the magnetic properties of 2 in the temperature range 1.9-295 K has shown the occurrence of a weak antiferromagnetic interaction [J = −0.066 cm⁻¹ with the Hamiltonian defined as H = −J ∑_i S_i · S_i+1] through the bis-bidentate croconate. The ability of the bis-chelating croconate to mediante magnetic interactions between paramagnetic first-row transition metal ions is discussed and compared to that of the related oxalate ligand.     

Interaction of gold(I) with thiosulfate-sulfite mixed ligand systems

The system was studied at 25 °C and at I = 0.1 M NaClO₄ using hydrodynamic voltammetry, gold potentiometry, UV-Vis spectrophotometry and Raman spectroscopy. The presence of two mixed-ligand species, Au(S₂O₃)(SO₃)³⁻ and , was detected from the Raman experiments and supported by the gold potentiometric experiments. The stepwise formation constant, log K_11r, for the reaction was found to be 1.1 (r = 1) and 4.8 (r = 2) from the hydrodynamic voltammetric experiments.     

Synthesis, crystal structures and magnetic properties of mononuclear tris(croconate)ferrate(III) complexes

A straightforward synthetic method to prepare mononuclear croconato-containing iron (III) complexes, (A)₃[Fe(C₅O₅)₃] [A = tetrabutylammonium = n-Bu₄N⁺ (1) and along with their crystal structures and magnetic properties, are reported. The Fe(III) atom adopts a pseudo-octahedral geometry while magnetic susceptibility measurements, in the 2-300 K temperature range, show the occurrence of a high spin state (S = 5/2) in both complexes.     

Kinetic studies of the reduction of hexaaquacobalt(III) perchlorate by a cobaloxime, [Co(dmgBF2)2(H2O)2]

The reaction of with Co(dmgBF₂)₂(H₂O)₂ in 1.0 M HClO₄/LiClO₄ was found to be first-order in both reactants and the [H⁺] dependence of the second-order rate constant is given by k_2obs = b/[H⁺], b at 25 °C is 9.23 ± 0.14 × 10² s⁻¹. The [H⁺] dependence at lower temperatures shows some saturation effect that allowed an estimate of the hydrolysis constant for as K_a = 9.5 × 10⁻³ M at 10 and 15 °C. Marcus theory and the known self-exchange rate constant for Co(OH₂)₅OH^2+/+ were used to estimate an electron self-exchange rate constant of k₂₂ = 1.7 × 10⁻⁴ M⁻¹ s⁻¹ for .     

3D coordination polymer of copper (II)-potassium (I): Crystal structure and thermal decomposition kinetics

A new heterometallacrown coordination polymer [K₂Cu(NPA)₂(H₂O)₄]_n (where H₂NPA = 3-nitro-phthalic acid) has been synthesized and it’s crystal structure has been elucidated. In the complex, the o-phthalate group coordinates to metal atoms behaving as both tetradentate and heptadentate coordination, the modes of which have been found for the first time. The thermal behaviors of this complex and the thermal decomposition kinetics have been studied. Kinetic analysis shows that the decomposition of title complex in the main range acts as two separate transitions with the first one being a double-step following reaction, , and the second being a three-step following reaction of t:f,f, . The kinetic parameters of these processes were also obtained.     

Dinuclear gold(III) pyrazolato complexes - Synthesis, structural characterization and transformation to their trinuclear gold(I) and gold(I/III) analogues

The reaction of AuCl₃py with Na(pz∗) (pz∗ = pyrazolato, or substituted pyrazolato anion) yields stable dinuclear [cis-Au^IIICl₂(μ-pz∗)]₂ complexes. In the presence of a base, the latter undergo reduction with concomitant transformation of the dinuclear -structure to trinuclear Au^I, Au^III (containing trans Au^IIICl₂-centres) and species.     

Effects of bis(salicylidene)trimethylenediamine and 2,2′-bipyridyl on luminescence and extraction of tris(pivaloyltrifluoroacetonato)Eu(III)

The UV, excitation and luminescence spectra of EuA₃B to be the extracted species as well as the extraction of Eu(III) with pivaloyltrifluoroacetone, HA, and/or Lewis bases, B (2,2′-bipyridyl, bpy, and bis(salicylidene)trimethylenediamine, H₂saltn) into CHCl₃ were measured. The results are summarized: the stability constants of EuA₃bpy and EuA₃H₂saltn complexes are 5.85 ± 0.05 and 2.95 ± 0.06 as , respectively. The present results suggest that because of intramolecular hydrogen bonding, the stability and luminescence of the H₂saltn complex including the quantum yield are smaller than those of the bpy complex. The weaker luminescence is also concerned with the fact that the less stable complexes easily dissociate in solvents to diminish the essential concentration.     

Rare earth complexation with 1,3,5-trideoxy-1,3,5-tris(2-hydroxybenzyl)amino-cis-inositol

The protonation constants of 1,3,5-trideoxy-1,3,5-tris(2-hydroxyl-benzyl)amino-cis-inositol (thci) in I = 1 M (NaClO₄) were determined to be: pK_a1 5.96 ± 0.03, pK_a2 7.21 ± 0.01, pK_a3 8.32 ± 0.07, pK_a4 8.95 ± 0.06. The solvent extraction studies were consistent with the formation of the Ln(thci)³⁺ and complexes. The log of the stability constants (log β₁ and log β₂) at 25 °C in 1 M (NaClO₄) at pH 4 for formation of these complexes are reported. Laser luminescence measurements of the ⁷F₀-⁵D₀ transition of Eu(III) complexed by thci indicated two species. The shifts in the peaks relative to that of Eu(aq)³⁺ were comparable to the values reported for other complexes of Eu(III) with organic ligands, but the intensities were greater. Luminescence lifetime measurements of the fluorescence spectra indicated that the complex has 5 inner sphere water molecules bound to the Eu(III) cation at pH 6.71-8.52. This was consistent with bidentate chelation of Eu(III) with each thci molecule. gaussian view energy calculations indicated bonding for M(III) to the amino and hydroxyl groups of the cyclohexanetriol and (2-hydroxybenzyl)amino moieties in the Ln(thci)³⁺ complex.     

Molecular structure and linkage isomerization of isothiocyanato(3-thiapentane-1,5-dithiolato)oxorhenium(V) complex

The properties of isothiocyanato(3-thiapentane-1,5-dithiolato)oxorhenium(V) [ReO(SSS)NCS, (1a), (3+1) type], where isothiocyanato occupies the fifth position, have been studied. Two linkage isomers, i.e., ReO(SSS)NCS (1a) and ReO(SSS)SCN (1b), were found to be formed during syntheses. The sufficient quantities of 1a were isolated in the solid state, and characterized by X-ray crystallography and IR spectroscopy. From ¹H and ¹⁵N NMR measurements, it was found that 1a is in equilibrium with 1b in liquid state. In the solvents with low dielectric constant such as CH₂Cl₂, only 1a isomer was detected, while in the solvents with high such as CH₃CN, both 1a and 1b isomers were observed. We have obtained the equilibrium constant (K_iso) for the linkage isomerization reaction in CD₃CN by measuring ¹⁵N NMR spectra at various temperatures. The values of K_iso at 25 °C, the standard enthalpy (ΔH^°), and the standard entropy (ΔS^°) for the isomerization equilibrium were evaluated as 0.409, 14.4 kJ mol⁻¹, and 40.9 J K⁻¹ mol⁻¹, respectively.     

Syntheses and structural determination of new bis(9-tungstoarsenato)tris(dioxouranate(VI)) and its monooxovanadate(IV) derivative complexes

The [As₂W₁₈U₃O₇₄]¹²⁻ complex is formed by the “self-assembly” reaction of and (uranyl nitrate) ions in acidic media. The anion complex is isolated as the potassium salt and characterized by elemental analysis, IR, UV-Vis, and X-ray single crystal analysis. The complex contains an anion in which three ions are unsymmetrically sandwiched between two A-α-[AsW₉O₃₄]⁹⁻ groups leading to a structure of C_3v symmetry. Each uranium atom adopts pentagonal-bipyramidal coordination, achieved by three equatorial bonds to one [AsW₉O₃₄]⁹⁻and two bonds to the other. The [As₂W₁₈U₂V₂O₇₃]¹²⁻and also [As₂W₁₈U₃O₇₄]¹²⁻ complexes are formed also, by reaction of the [KAs₂W₁₈U₂O₇₂]¹³⁻ with VO²⁺ and ions in 1:1 mole ratio. The cyclic voltammogram of [As₂W₁₈U₂VO₇₃]¹²⁻ in acetate buffer (pH 4.7) shows a reversible one-electron redox process for V^IV/V couple at +0.396 (E_pc) and +0.432 V (E_pa).     

Comprehensive inhibitor profiling of the Proteus mirabilis metalloprotease virulence factor ZapA (mirabilysin)

In this study we report for the first time the comprehensive inhibitor profiling of the Proteus mirabilis metalloprotease virulence factor ZapA (mirabilysin) using a 160 compound focused library of N-alpha mercaptoamide dipeptides, in order to map the and binding site preferences of this important enzyme. This study has revealed a preference for the aromatic residues tyrosine and tryptophan in and aliphatic residues in . From this library, six compounds were identified which exhibited sub- to low-micromolar K_i values. The most potent inactivator, SH–CO₂–Y–V–NH₂ was capable of preventing ZapA-mediated hydrolysis of heat-denatured IgA, indicating that these inhibitors may be capable of protecting host proteins against ZapA during colonisation and infection.     

Synthesis and characterization of four novel mixed (porphyrinato)(phthalocyaninato) sandwich-type europium(III) complexes with [tetrakis(4-chlorophenyl)porphyrinato] and diversely substituted phthalocyaninato ligands

Four novel mixed (porphyrinato)(phthalocyaninato) rare earth double-deckers Eu^III(TClPP)[Pc(t-BuPhO₂)₄] {H₂TClPP = tetrakis(4-chlorophenyl)porphyrin, H₂[Pc(t-BuPhO₂)₄] = 1,3,10,12(11,13),19,21(20,22),28,30(29,31)-octa-tert-butyl-tetrakis[1,4]benzodioxino[2,3-b:2′,3′-k:2″,3″-t:2?,3?-e₁]phthalocyanine}, HEu^III(TClPP)[Pc(α-OC₄H₉)₈] {H₂[Pc(α-OC₄H₉)₈] = 1,4,8,11,15,18,22,25-octa-butoxy-phthalocyanine}, Eu^III(TClPP)[Pc(MeOPhO)₈]{H₂[Pc(MeOPhO)₈] = 2,3,9,10,16,17,23,24-octakis(4-methoxyphenoxy)phthalocyanine} and Eu^III(TClPP)[Pc(PhS)₈] {H₂[Pc(PhS)₈] = 2,3,9,10,16,17,23,24-octakis(benzenesulfenyl)phthalocyanine} have been prepared for the first time by treating Eu(acac)(TClPP) with corresponding metal-free phthalocyanine in refluxing 1,2,4-trichlorobenzene (TCB). Typical IR marker bands of the monoanion radical , and show strong bands at 1310, 1319, and 1318 cm⁻¹, and are attributed to pyrrole CC stretchings. The TClPP⁻ IR marker band at ca. 1270-1300 cm⁻¹ was not observed for these compounds. These facts indicate that the hole in these double-deckers is mainly localized at the phthalocyanine ring. The marker IR band for phthalocyanine monoanionradical, , appearing at ca. 1312 cm⁻¹ as a medium absorption band was not observed for HEu^III(TClPP)[Pc(α-C₄H₉)₈]. Instead, a significant peak appearing at ca. 1321 cm⁻¹ with weak intensity is assigned to the pyrrole stretching of the phthalocyanine dianion, . This suggests that both the phthalocyanine and porphyrin rings exist as dianions in mixed (porphyrinato)(phthalocyaninato) complex, . The four complexes were characterized by MS, EA, UV-Vis and IR spectra.     

Re(I)(tricarbonyl) complexes with the 2-(2-pyridyl)-N-methyl-benzimidazole, 2-(2-pyridyl)benzoxazole and 2-(2-pyridyl)benzothiazole ligands - syntheses, structures, electrochemical and spectroscopic studies

The reactions of Re(CO)₅Cl with the chelating ligands 2-(2-pyridyl)-N-methylbenzimidazole, 2-(2-pyridyl)benzoxazole and 2-(2-pyridyl)benzothiazole afforded neutral fac-Re(CO)₃(L)Cl and ionic complexes with structures confirmed by means of X-ray measurements. UV-vis absorption and emission properties have been studied at room and 77 K temperatures in order to determine the nature of the lowest electronically excited states. Electrochemical behaviour of the investigated fac-Re(CO)₃(L)Cl and complexes has been studied using cyclic and square-wave voltammetry. Preliminary results from the electrogenerated chemiluminescence studies of the ionic and the neutral fac-Re(CO)₃(MPBI)Cl complexes are briefly presented.     

The BK channel accessory β1 subunit determines alcohol-induced cerebrovascular constriction

Ethanol-induced inhibition of myocyte large conductance, calcium- and voltage-gated potassium (BK) current causes cerebrovascular constriction, yet the molecular targets mediating EtOH action remain unknown. Using BK channel-forming (cbv1) subunits from cerebral artery myocytes, we demonstrate that EtOH potentiates and inhibits current at lower and higher than ∼15 μM, respectively. By increasing cbv1’s apparent -sensitivity, accessory BK β₁ subunits shift the activation-to-inhibition crossover of EtOH action to <3 μM , with consequent inhibition of current under conditions found during myocyte contraction. Knocking-down KCNMB1 suppresses EtOH-reduction of arterial myocyte BK current and vessel diameter. Therefore, BK β₁ is the molecular effector of alcohol-induced BK current inhibition and cerebrovascular constriction.     

Squarato-metal(II) complexes. 1: Structural and magnetic characterization of squarato-bridged dinuclear nickel(II) and copper(II) complexes

A new series of dinuclear squarato-bridged nickel(II) and copper(II) complexes [Ni₂(2,3,2-tet)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂ (1), [Ni₂(aepn)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂ (2), [Cu₂(pmedien)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂.4H₂O (3) and [Cu₂(DPA)₂(μ_1,2-C₄O₄)(H₂O)₂](ClO₄)₂ (4) where is the dianion of 3,4-dihydroxycyclobut-3-en-1,2-dione (squaric acid), 2,3,2-tet = 1,4,8,11-tetraazaundecane, aepn = N-(2-aminoethyl)-1,3-propanediamine, pmedien = N,N,N′,N″,N″-pentamethyldiethylenetriamine and DPA = di(2-pyridylmethyl)amine were synthesized and structurally characterized by X-ray crystallography. The spectral and structural characterization as well as the magnetic behaviour of these complexes is reported. In this series, structures consist of the groups as counter ions and the bridging the two M(II) centers in a μ-1,3- (1-3) and in a μ-1,2-bis(monodentate) (4) bonding fashions. The coordination geometry around the Ni(II) ions in 1 and 2 is six-coordinate with distorted octahedral environment achieved by N atoms of the amines and by one or two oxygen atoms from coordinated water molecules, respectively. In the Cu(II) complexes 3 and 4, a distorted square pyramidal geometry is achieved by the three N-atoms of the aepn or DPA and by an oxygen atom from a coordinated water molecule. The electronic spectra of the complexes in aqueous solutions are in complete agreement with the assigned X-ray geometry around the M(II) centers. The complexes show weak antiferromagnetic coupling with ∣J∣ = 1.8-4.2 cm⁻¹ in the μ-1,3- bridged squarato compounds 1-3, and J = −16.1 cm⁻¹ in the corresponding μ-1,2- bridged squarato complex 4. The magnetic properties are discussed in relation to the structural data.     

In situ spectroelectrochemical investigation of Pt(II/IV) oxidation in aqueous solution using X-ray absorption spectroscopy

The oxidation from to in HCl aq. was studied in situ by combining electrochemistry with XAFS spectroscopy. During the oxidation of , isosbestic points were observed in Pt L_III and L_II XANES spectra as a function of time, indicating that the Pt(II/IV) redox equilibrium is the only reaction in the system. The Pt L_III and L_II X-ray absorption edge energies of the initial Pt^IICl₄²⁻ are 11562.9 and 13271.8 eV, respectively, while those of the electrolyzed species are 11564.6 and 13273.7 eV which are identical with those of a reference sample. The coordination of the electrolyzed species was characterized by structural parameters derived from the EXAFS curve fit, and identified to .     

A new Cu(4,5-diazafluoren-9-one)-capped Keggin derivative: Hydrothermal synthesis and crystal characterization

A new α-Keggin POM derivative (1) (DF = 4,5-diazafluoren-9-one) has been prepared under hydrothermal conditions and characterized by single-crystal X-ray diffraction, elemental analysis, IR, XPS spectra, thermogravimetric analysis and cyclic voltammetry. In compound 1, the polyoxoanion cluster is decorated by a single capping {Cu(DF)}²⁺ subunit via four bridging oxygen atoms on a {Mo₄O₄} pit. The isolated copper dimer unit acts as counter cation, in which the organic ligand DF exhibits a rare coordination mode. Furthermore, the capped Keggin polyoxoanions are fused together via the copper dimers through the weak Cu ? O interactions to form chains. Hybrid 1 was used as a solid bulk modifier to fabricate a carbon paste electrode (1-CPE) by direct mixing. The electrochemical and electrocatalytic behaviors of the 1-CPE have been studied in detail.     

Oxomolybdenum(III, IV and V) complexes of thiofunctional ligands

Reaction of [MoO₂(acac)₂] with (S is a thioether, S′ a thiophenolate function) yielded the compound Li₇(thf)₁₇{MoO}₈ · 10thf · hexane, where {MoO}₈ represents one 1, three (2, linked, via the oxo group, to [Li(thf)₃]⁺) and two (3a, linked by two [Li(thf)₂]⁺).A mixed-valent variant of 3, (3b, with an additional[Li(thf)₃]⁺ attached to S′), was also identified. The compounds model features pertinent to oxo-transferases containing the molybdopterin cofactor.