Microbial treatment of high-strength perchlorate wastewater

To treat wastewater containing high concentrations of perchlorate, a perchlorate reducing-bacterial consortium was obtained by enrichment culture grown on high-strength perchlorate (1200 mg L⁻¹) feed medium, and was characterized in a sequence batch reactor (SBR) over a long-time operation. The consortium removed perchlorate in the SBR with high reduction rates (35-90 mg L⁻¹ h⁻¹) and stable removal efficiency over 200-day operations. The maximum specific perchlorate reduction rate (q_max), half saturation constant (K_s), and optimal pH range were 0.67 mg-perchlorate mg-dry cell weight⁻¹ h⁻¹, 193.8 mg-perchlorate L⁻¹, and pH 7-9, respectively. The perchlorate reduction yield was 0.48 mol-perchlorate mol-acetate⁻¹. A clone library prepared using the amplicons of cld gene encoding chlorate dismutase showed that the dominant (per)chlorate reducing bacteria in the consortium were Dechlorosoma sp. (53%), Ideonella sp. (28%), and Dechloromonas sp. (19%).     

Uptake of perchlorate from aqueous solutions by amine-crosslinked cotton stalk

Virgin cotton stalk was produced into an effective biosorbent for perchlorate adsorption. Surface analysis including BET surface area and SEM illustrated the reduction of porous structure in amine-crosslinked cotton stalk (AC-CS). Elemental and zeta potential analysis validated the graft of some positively charged amine groups on surface of AC-CS. Spectra analysis (XPS, FTIR and Raman spectra) suggested that interaction between AC-CS and ClO₄⁻ should be based on electrostatic attraction. The maximum adsorption capacity (q_max) of AC-CS for perchlorate at different pHs (3.0, 6.0, 9.0 and 11.0) were calculated as 29.6, 42.6, 41.0 and 33.0 mg/g, respectively. The saturated perchlorate uptakes in column were in range of 25.0–38.1 mg/g at different pHs. In addition, the exhausted AC-CS column was regenerated by 0.5 mol/L of NaCl solution, which was adequate for almost complete desorption of the perchlorate.     

A method for assaying perchlorate concentration in microbial cultures using the fluorescent dye resazurin

Low concentrations (μg/L) of the perchlorate anion, ClO₄⁻, have been measured in surface and ground water supplies in many locations throughout the United States. Perchlorate is known to affect the function of the thyroid gland in mammals and its toxicity primarily results from its inhibition of thyroid hormone output. The major sources of perchlorate contamination in surface and ground waters are defense contractors, military installations, propellant manufacturers and agriculture. The currently accepted method of perchlorate analysis, recommended by the US EPA, is neither fast nor easy to use and requires purchase of an expensive high performance ion chromatograph (IC). The novel method described here uses dye resazurin to measure perchlorate reduction by bacterial cultures and bacterial consortia in a high-throughput, multi-well, culture plate format. The method is based on the observation that perchlorate reduction and the decrease of resazurin fluorescence occur simultaneously in perchlorate degrading cultures. The bioassays were performed in anaerobic serum bottles or 96-well plates with constant shaking, using a minimal ATCC medium with 10 mM acetate as electron donor/carbon source and 200 ppm perchlorate as an electron acceptor. Fluorescence measurements with excitation at 570 nm and emission at 590 nm were taken in 20 min intervals. Changes in perchlorate concentration were confirmed using IC. Based on the experimental data, a simple model showing the correlation between perchlorate concentration in microbial culture and resazurin fluorescence level was proposed. Other dyes including redox indicators, reactive azo dyes and electron shuttle chemicals were also tested for comparison and were found less useful.     

Structures of homoleptic eight- and nine-coordinate uranium(IV) perchlorate complexes with sulfoxide molecules as ligands

Homoleptic eight- and nine-coordinate U(IV) perchlorate complexes with sulfoxide ligands have been characterized crystallographically. Crystals of [U(dmso)₈](ClO₄)₄ · 0.75CH₃NO₂, [U(dmso)₉](ClO₄)₄ · 4dmso (dmso = dimethyl sulfoxide), and [U(tmso)₈](ClO₄)₄ · 2tmso (tmso = tetramethylene sulfoxide) were found to have dodecahedral, tricapped trigonal prismatic, and square antiprismatic geometries, respectively. Average U-O bond distances in [U(dmso)₈](ClO₄)₄ · 0.75CH₃NO₂, [U(dmso)₉](ClO₄)₄ · 4dmso, and [U(tmso)₈](ClO₄)₄ · 2tmso are 2.35(3), 2.41 (4), and 2.35(3) Å, respectively. Furthermore, it was found that [U(dmso)₈]⁴⁺ is in equilibrium with [U(dmso)₉]⁴⁺ in CH₃NO₂ solution containing dmso. Thermodynamic parameters for such an equilibrium are as follows: K (25 °C) = 3.4 ± 0.2 dm³ mol⁻¹, ΔH = −54.9 ± 4.5 kJ mol⁻¹, and ΔS = −174 ± 15 J K⁻¹ mol⁻¹.     

Synthesis, crystal structure and magnetic properties of new dinuclear Mn(III) compounds with 4-ClC6H4COO and 4-BrC6H4COO bridges

Four new dinuclear Mn(III) compounds have been synthesised: [{Mn(bpy)(H₂O)}₂(μ-4-ClC₆H₄COO)₂(μ-O)}](ClO₄)₂ (1), [{Mn(EtOH)(phen)}₂(μ-O)(μ-4-ClC₆H₄COO)₂](ClO₄)₂ (2), [{Mn(bpy)(EtOH)}(μ-4-BrC₆H₄COO)₂(μ-O){Mn(bpy)(ClO₄)](ClO₄) (3) and [{Mn(H₂O)(phen)}₂(μ-4-BrC₆H₄COO)₂(μ-O)](ClO₄)₂ (4). The crystal structures of 2 and 3 are evidence for the tendency of the ethanol and the perchlorate to act as ligands. Due to the coordination of these groups, the environment of the manganese ions is elongated in the monodentate ligand direction, and this distortion is more important when this ligand is the perchlorate. The magnetic properties of the four compounds have been analysed: compounds 1, 3 and 4 show antiferromagnetic behaviour, with J = −6.33 cm⁻¹ for 1, J = −6.76 cm⁻¹ for 3 and J = −3.08 cm⁻¹ for 4 (H = −JS₁·S₂), while compound 2 shows a very weak ferromagnetic coupling. For this compound, at low temperature the most important effect on the χ_MT data is the zero-field splitting of the ion, and the best fit was obtained with |D_Mn| = 2.38 cm⁻¹ and |E_Mn| = 0.22 cm⁻¹.     

A new tetranuclear copper(II) complex with oximate bridges: Structure, magnetic properties and DFT study

A new tetranuclear complex, [Cu₄L₄](ClO₄)₄·2H₂O (1), has been synthesized from the self-assembly of copper(II) perchlorate and the tridentate Schiff base ligand (2E,3E)-3-(2-aminopropylimino) butan-2-one oxime (HL). Single-crystal X-ray diffraction studies reveal that complex 1 consists of a Cu₄(NO)₄ core where the four copper(II) centers having square pyramidal environment are arranged in a distorted tetrahedral geometry. They are linked together by a rare bridging mode (μ₃-η¹,η²,η¹) of oximato ligands. Analysis of magnetic susceptibility data indicates moderate antiferromagnetic (J₁ = −48 cm⁻¹, J₂ = −40 cm⁻¹ and J₃ = −52 cm⁻¹) exchange interaction through σ-superexchange pathways (in-plane bridging) of the oxime group. Theoretical calculations based on DFT technique have been used to obtain the energy states of different spin configurations and estimate the coupling constants and to understand the exact magnetic exchange pathways.     

Formation of a supramolecular ladder using dinuclear dicyanamide bridged Cu(II) species: Synthesis, crystal structure and magnetic property

The reaction of Cu(ClO₄)₂ · 6H₂O with bis(3-aminopropyl)methylamine and sodium dicyanamide in aqueous medium results in the formation of a dimeric dicyanamide complex of Cu(II), [Cu₂(medpt)₂(dca)₂](ClO₄)₂. The single crystal X-ray structure reveals that the dinuclear entities are extended to form a supramolecular 1D ladder by H-bonding. Each dinuclear entity is joined to the adjacent unit via the perchlorate anion. Variable temperature magnetic study was performed and the best-fit parameters are J = −1.20 ± 0.02 cm⁻¹, g = 2.08 ± 0.01 with R = 2 × 10⁻⁵. These clearly indicate the antiferromagnetic interaction between the Cu(II) center.     

Synthesis and characterization of chromium(III) octaphenylporphyrin complexes with various axial ligands: An insight into porphyrin distortion

Influence of axial ligands, MeCN, H₂O, py, and piperidine (pip), on distortion of (2,3,5,10,12,13,15,20-octaphenylporphinato)chromium(III), [Cr(OPP)]⁺, was investigated by X-ray crystallography and UV-vis and ESR spectroscopies. In crystal structures of [Cr(OPP)(MeCN)(H₂O)]ClO₄ · MeCN and [Cr(OPP)(H₂O)₂]ClO₄ · 3THF, the OPP²⁻ ligand had a planar structure. On the other hand, crystal structures of [Cr(OPP)(pip)₂]ClO₄ · 2CH₂Cl₂ and [Cr(OPP)(py)₂]ClO₄ exhibited a waved structure and a saddle-shaped structure with ruffling, respectively. In the UV-vis spectrum of [Cr(OPP)(py)₂]ClO₄ in CH₂Cl₂, the large red shift of the Soret band was observed. Furthermore, the small D value of 0.10 cm⁻¹ was obtained for [Cr(OPP)(py)₂]ClO₄ from the ESR spectrum in frozen 1,2-dichloroethane solution at 5 K. These results suggest that the OPP²⁻ ligand is distorted both in solid and in solution, and that the axial ligand would exert some effects on the porphyrin distortion.     

Tetra-, penta- and hexacoordinate copper(II) complexes with N3 donor isoindoline-based ligands: Characterization and SOD-like activity

Reaction of 1,3-bis(2′-Ar-imino)isoindolines (HLⁿ, n = 1-7, Ar = benzimidazolyl, N-methylbenzimidazolyl, thiazolyl, pyridyl, 3-methylpyridyl, 4-methylpyridyl, and benzthiazolyl, respectively) with Cu(OCH₃)₂ yields mononuclear hexacoordinate complexes with Cu(Lⁿ)₂ composition. With cupric perchlorate square-pyramidal [Cu^II(HLⁿ)(NCCH₃)(OClO₃)]ClO₄ complexes (n = 1, 3, 4) were isolated as perchlorate salts, whereas with chloride Cu^II(HLⁿ)Cl₂ (n = 1, 4), or square-planar Cu^IICl₂(HLⁿ) (n = 2, 3, 7) complexes are formed. The X-ray crystal structures of Cu(L³)₂, Cu(L⁵)₂, [Cu^II(HL⁴)(NCCH₃)(OClO₃)]ClO₄, Cu^IICl(L²) and Cu^IICl(L⁷) are presented along with electrochemical and spectral (UV-Vis, FT-IR and X-band EPR) characterization for each compound. When combined with base, the isoindoline ligands in the [Cu^II(HLⁿ)(NCCH₃)(OClO₃)]ClO₄ complexes undergo deprotonation in solution that is reversible and induces UV-Vis spectral changes. Equilibrium constants for the dissociation are calculated. X-band EPR measurements in frozen solution show that the geometry of the complexes is similar to the corresponding X-ray crystallographic structures. The superoxide scavenging activity of the compounds determined from the McCord-Fridovich experiment show dependence on structural features and reduction potentials.     

Hydrothermal synthesis and crystal structures of two lanthanide coordination polymers with novel tetradentate-coordinated perchlorates

Two new 3D lanthanide coordination polymers {[Ln(C₂O₄)(ClO₄)(H₂O)] · Cl}_n [Ln = Pr (1) and Nd (2)] have been synthesized by hydrothermal reactions and characterized by elemental analysis, X-ray single-crystal analyses, IR and Raman spectroscopy. X-ray crystal structure analyses reveal that compounds 1 and 2 are isostructural and crystallized in the space group P2₁/c. A 1D zigzag chains formed by oxalate ligands in μ₂-mode to bridge Ln(III) atoms present in the two complexes and the adjacent zigzag chains were further connected by μ₃-η¹:η¹:η¹:η¹ fashion of into a 3D framework with ordered 1D channels, in which uncoordinated Cl⁻ anions are located as counterions. In addition, the IR and Raman spectrum further confirm the presence of tetradentate-coordinated perchlorates.     

Kinetic study of dissociation of Eu(III) complex with H8dotp (H8dotp = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylphosphonic acid))

The dissociation kinetics of the europium(III) complex with H₈dotp ligand was studied by means of molecular absorption spectroscopy in UV region at ionic strength 3.0 mol dm⁻³ (Na,H)ClO₄ and in temperature region 25-60 °C. Time-resolved laser-induced fluorescence spectroscopy (TRLIFS) was employed in order to determine the number of water molecules in the first coordination sphere of the europium(III) reaction intermediates and the final products. This technique was also utilized to deduce the composition of reaction intermediates in course of dissociation reaction simultaneously with calculation of rate constants and it demonstrates the elucidation of intimate reaction mechanism. The thermodynamic parameters for the formation of kinetic intermediate (ΔH⁰ = 11 ± 3 kJ mol⁻¹, ΔS⁰ = 41 ± 11 J K⁻¹ mol⁻¹) and the activation parameters (E_a = 69 ± 8 kJ mol⁻¹, ΔH^≠ = 67 ± 8 kJ mol⁻¹, ΔS^≠ = −83 ± 24 J K⁻¹ mol⁻¹) for the rate-determining step describing the complex dissociation were determined. The mechanism of proton-assisted reaction was proposed on the basis of the experimental data.     

Structural characterization, electrochemistry, and spectroelectrochemistry of trans-dioxorhenium(V) complex with 4-methoxypyridine, [ReO2(4-MeOpy)4]PF6, and characterization of [ReO2(4-MeOpy)4] generated electrochemically

Crystal structure of [ReO₂(4-MeOpy)₄][PF₆] (4-MeOpy = 4-methoxypyridine) complex has been examined by the single crystal X-ray analytical method. This complex shows a trans-dioxo geometry (average Re-O bond length = 1.766(2) Å) and its equatorial plane is occupied by four 4-MeOpy molecules (average Re-N bond length = 2.156(4) Å). Electrochemical reaction of [ReO₂(4-MeOpy)₄]⁺ in CH₃CN solution containing tetra-n-butylammonium perchlorate as a supporting electrolyte has been studied using cyclic voltammetry at 24 °C. Cyclic voltammograms show one redox couple around 0.65 V (E_pa) and 0.58 V (E_pc) [versus ferrocene/ferrocenium ion redox couple, (Fc/Fc⁺)]. Potential differences between two peaks (ΔE_p) at scan rates in the range from 0.01 to 0.10 V s⁻¹ are 65 mV, which is almost consistent with the theoretical ΔE_p value (59 mV) for the reversible one electron transfer reaction at 24 °C. The ratio of anodic peak currents to cathodic ones is 1.04 ± 0.03 and the (E_pa + E_pc)/2 value is constant, 0.613 ± 0.001 V versus Fc/Fc⁺, regardless of the scan rate. Spectroelectrochemical experiments have also been carried out by applying potentials from 0.40 to 0.77 V versus Fc/Fc⁺ with an optically transparent thin layer electrode. It was found that the UV-visible absorption spectra show clear isosbestic points at 228, 276, and 384 nm, and that the electron stoichiometry is evaluated as 1.03 from the Nernstian plot. These results indicate that the [ReO₂(4-MeOpy)₄]⁺ complex is oxidized reversibly to the [ReO₂(4-MeOpy)₄]²⁺ complex. Furthermore, it was clarified that the [ReO₂(4-MeOpy)₄]²⁺ in CH₃CN has the characteristic absorption bands at 236, 278, 330, 478, and 543 nm and their molar absorption coefficients are 4.3 × 10⁴, 4.5 × 10³, 1.0 × 10⁴, and 6.1 × 10³ M⁻¹ cm⁻¹ (M = mol dm⁻³), respectively.     

Homoleptic copper(II) and copper(I) complexes of 5,6-dihydro-5,6-epoxy-1,10-phenanthroline. Six-coordinate copper(I) in solution

Reaction of 5,6-dihydro-5,6-epoxy-1,10-phenanthroline (L) with Cu(ClO₄)₂·6H₂O in methanol in 3:1 M ratio at room temperature yields light green [CuL₃](ClO₄)₂·H₂O (1). The X-ray crystal structure of the hemi acetonitrile solvate [CuL₃](ClO₄)₂·0.5CH₃CN has been determined which shows Jahn-Teller distortion in the CuN₆ core present in the cation [CuL₃]²⁺. Complex 1 gives an axial EPR spectrum in acetonitrile-toluene glass with g_|| = 2.262 (A_|| = 169 × 10⁻⁴ cm⁻¹) and g_⊥ = 2.069. The Cu(II/I) potential in 1 in CH₂Cl₂ at a glassy carbon electrode is 0.32 V versus NHE. This potential does not change with the addition of extra L in the medium implicating generation of a six-coordinate copper(I) species [CuL₃]⁺ in solution. B3LYP/LanL2DZ calculations show that the six Cu-N bond distances in [CuL₃]⁺ are 2.33, 2.25, 2.32, 2.25, 2.28 and 2.25 Å while the ideal Cu(I)-N bond length in a symmetric Cu(I)N₆ moiety is estimated as 2.25 Å. Reaction of L with Cu(CH₃CN)₄ClO₄ in dehydrated methanol at room temperature even in 4:1 M proportion yields [CuL₂]ClO₄ (2). Its ¹H NMR spectrum indicates that the metal in [CuL₂]⁺ is tetrahedral. The Cu(II/I) potential in 2 is found to be 0.68 V versus NHE in CH₂Cl₂ at a glassy carbon electrode. In presence of excess L, 2 yields the cyclic voltammogram of 1. From ¹H NMR titration, the free energy of binding of L to [CuL₂]⁺ to produce [CuL₃]⁺ in CD₂Cl₂ at 298 K is estimated as −11.7 (±0.2) kJ mol⁻¹.     

Formation of a wrapped DNA-protein interface: experimental characterization and analysis of the large contributions of ions and water to the thermodynamics of binding IHF to H' DNA

To characterize driving forces and driven processes in formation of a large-interface, wrapped protein-DNA complex analogous to the nucleosome, we have investigated the thermodynamics of binding the 34-base pair (bp) H′ DNA sequence to the Escherichia coli DNA-remodeling protein integration host factor (IHF). Isothermal titration calorimetry and fluorescence resonance energy transfer are applied to determine effects of salt concentration [KCl, KF, K glutamate (KGlu)] and of the excluded solute glycine betaine (GB) on the binding thermodynamics at 20 °C. Both the binding constant K_obs and enthalpy ΔH°_obs depend strongly on [salt] and anion identity. Formation of the wrapped complex is enthalpy driven, especially at low [salt] (e.g., ΔH^o_obs = − 20.2 kcal·mol^− 1 in 0.04 M KCl). ΔH°_obs increases linearly with [salt] with a slope (dΔH°_obs/d[salt]), which is much larger in KCl (38 ± 3 kcal·mol^− 1 M^− 1) than in KF or KGlu (11 ± 2 kcal·mol^− 1 M^− 1). At 0.33 M [salt], K_obs is approximately 30-fold larger in KGlu or KF than in KCl, and the [salt] derivative SK_obs = dlnK_obs/dln[salt] is almost twice as large in magnitude in KCl (− 8.8 ± 0.7) as in KF or KGlu (− 4.7 ± 0.6).A novel analysis of the large effects of anion identity on K_obs, SK_obs and on ΔH°_obs dissects coulombic, Hofmeister, and osmotic contributions to these quantities. This analysis attributes anion-specific differences in K_obs, SK_obs, and ΔH°_obs to (i) displacement of a large number of water molecules of hydration [estimated to be 1.0(± 0.2) × 10³] from the 5340 Å² of IHF and H′ DNA surface buried in complex formation, and (ii) significant local exclusion of F⁻ and Glu⁻ from this hydration water, relative to the situation with Cl⁻, which we propose is randomly distributed. To quantify net water release from anionic surface (22% of the surface buried in complexation, mostly from DNA phosphates), we determined the stabilizing effect of GB on K_obs: dlnK_obs/d[GB]  = 2.7 ± 0.4 at constant KCl activity, indicating the net release of ca. 150 H₂O molecules from anionic surface.     

Structure and magnetism of two new linear trinuclear copper(II) clusters obtained from the tetradentate N2O2 ligand bis(2-hydroxybenzyl)-1,3-diaminopropane

Reaction of bis(2-hydroxybenzyl)-1,3-diaminopropane (H₂bhbd) with copper(II) perchlorate and copper(II) chloride in methanol, respectively, leads to linear trinuclear clusters, namely [Cu₃(bhbd)₂(CH₃OH)₂(ClO₄)₂] (1) and [Cu₃(bhbd)₂Cl₂](CH₃OH)₄ (2). These coordination compounds were characterized by X-ray crystallography, UV-Vis, IR and EPR spectroscopy, and magnetic susceptibility measurements. Both complexes have a linear trinuclear array of copper ions bridged by means of phenolato O atoms and separated by a distance of 2.985(4) Å (1) and 2.937(4) Å (2). Strong antiferromagnetic interactions between these adjacent Cu^II ions govern the magnetochemistry of 1 (J = −303(1) cm⁻¹) and 2 (J = −482(3) cm⁻¹) resulting in S = 1/2 ground states fully populated below 150 K. A correlation between the interaction parameter J and the angles within the trinuclear clusters is proposed.     

Mono, di and polynuclear Cu(II)-azido complexes incorporating N,N,N reduced schiff base: syntheses, structure and magnetic behavior

Three kinds of copper(II) azide complexes have been synthesised in excellent yields by reacting Cu(ClO₄)₂ · 6H₂O with N,N-bis(2-pyridylmethyl)amine (L¹); N-(2-pyridylmethyl)-N′,N′-dimethylethylenediamine (L²); and N-(2-pyridylmethyl)-N′,N′-diethylethylenediamine (L³), respectively, in the presence of slight excess of sodium azide. They are the monomeric Cu(L¹)(N₃)(ClO₄) (1), the end-to-end diazido-bridged Cu₂(L²)₂(μ-1,3-N₃)₂(ClO₄)₂ (2) and the single azido-bridged (μ-1,3-) 1D chain [Cu(L³)(μ-1,3-N₃)]_n(ClO₄)_n (3). The crystal and molecular structures of these complexes have been solved. The variable temperature magnetic moments of type 2 and type 3 complexes were studied. Temperature dependent susceptibility for 2 was fitted using the Bleaney-Bowers expression which led to the parameters J = −3.43 cm⁻¹ and R = 1 × 10⁻⁵. The magnetic data for 3 were fitted to Baker’s expression for S = 1/2 and the parameters obtained were J = 1.6 cm⁻¹ and R = 3.2 × 10⁻⁴. Crystal data are as follows. Cu(L¹)(N₃)(ClO₄): Chemical formula, C₁₂H₁₃ClN₆O₄Cu; crystal system, monoclinic; space group, P2₁/c; a = 8.788(12), b = 13.045(15), c = 14.213(15) Å; β = 102.960(10)°; Z = 4. Cu(L²)(μ-N₃)(ClO₄): Chemical formula, C₁₀H₁₇ClN₆O₄Cu: crystal system, monoclinic; space group, P2₁/c; a = 10.790(12), b = 8.568(9), c = 16.651(17) Å; β = 102.360(10)°; Z = 4. [Cu(L³)(μ-N₃)](ClO₄): Chemical formula, C₁₂H₂₁ClN₆O₄Cu; crystal system, monoclinic; space group, P2₁/c; a = 12.331(14), b = 7.804(9), c = 18.64(2) Å; β = 103.405(10)°; Z = 4.     

Spectroscopic and magnetic properties of diethyl (pyridin-4-ylmethyl)phosphate (4-pmOpe) ligand with perchlorate transition metal salts. Crystal structure of [Cu(4-pmOpe)2(ClO4)2]

The perchlorate M(II) (M = Cu, Ni, Co) complexes with the diethyl (pyridin-4-ylmethyl)phosphate (4-pmOpe) ligand of the composition [M(4-pmOpe)₂ (H₂O)₂](ClO₄)₂ (M = Ni, Co) and [Cu(4-pmOpe)₂(ClO₄)₂] were prepared and studied. The ligand contains two donor atoms, i.e. pyridine nitrogen and phosphoryl oxygen atoms. In particular, the crystal structure of [Cu(4-pmOpe)₂(ClO₄)₂] was determined by the X-ray method. Its structure consists of a one-dimensional polymeric chain in which copper(II) ions are N,O-bridged by two 4-pmOpe organic ligands in a trans arrangement. Two perchlorate ions occupy the fifth and the sixth coordination sites. The Cu?Cu distance is 9.180 Å. The crystal packing is determined by the weak intermolecular C-H?O hydrogen contacts. The coordination compounds were identified and characterized by elemental analysis, spectroscopic and magnetic studies. Spectroscopic and magnetic results of the copper(II) compound are presented in the light of the crystal structure. The magnetic data indicate very weak intra- and interchain magnetic exchange interactions (J^’ = −0.43 and zJ^’ = 0.29 cm⁻¹, respectively). The spectroscopic and magnetic properties of the Co(II) and Ni(II) complexes indicate octahedral and polymeric structure of both compounds in which 4-pmOpe ligand also acts as N,O-bridge between metal ions.     

Synthesis, characterization, and crystal structure of a quadruply bonded dimolybdenum(II) complex containing the water-soluble phosphine 1,3,5-triaza-7-phosphaadamantane (PTA)

The quadruply bonded molybdenum(II)-molybdenum(II) complex, tetrachlorotetrakis(1,3,5-triaza-7-phosphaadamantane) dimolybdenum(II), Mo₂Cl₄(PTA)₄, was synthesized by reaction of 1,3,5-triaza-7-phosphaadamantane (PTA) with K₄[Mo₂Cl₈] in refluxing methanol. The complex was characterized using ¹H and ³¹P NMR, and UV-Vis spectroscopy, X-ray crystallography, and cyclic voltammetry. The Mo-Mo separation in the solid state structure is 2.13 Å, with the PTA and chloride ligands in an eclipsed arrangement with a P-Mo-Mo-Cl twist angle of 1.75(3)°. The ³¹P NMR spectrum contains a single peak at −62.8 ppm, and the ¹H NMR spectrum exhibits two singlets of equal height at 4.60 and 4.33 ppm. The UV-Vis spectrum contains three absorbance features at 615, 363, and 231 nm, with the absorbance at 615 nm due to the δ → δ* transition. The one electron oxidation of Mo₂Cl₄(PTA)₄ is reported at E_1/2 = 0.91 V relative to Ag/Ag⁺ in CH₂Cl₂. Also discussed is the reactivity of the molybdenum complex with CN⁻, H₂O, and HCl.     

Structure and magnetic properties of a tetranuclear Cu(II) complex containing the 2-(pyridine-2-yliminomethyl)-phenol ligand

A tetranuclear Cu(II) complex [Cu₄L₄(H₂O)₄](ClO₄)₄ has been synthesized using the terdentate Schiff base 2-(pyridine-2-yliminomethyl)-phenol (HL) (the condensation product of salicylaldehyde and 2-aminopyridine) and copper perchlorate. Chemical characterizations such as IR and UV/Vis of the complex have been carried out. A single-crystal diffraction study shows that the complex contains a nearly planar tetranuclear core containing four copper atoms, which occupy four equivalent five-coordinate sites with a square pyramidal environment. Magnetic measurements have been carried out over the temperature range 2-300 K and with 100 Oe field strengths. Analysis of magnetic susceptibility data indicates a strong antiferromagnetic (J₁ = −638 cm⁻¹) exchange interaction between diphenoxo-bridged Cu(II) centers and a moderate antiferromagnetic (J₂ = −34 cm⁻¹) interaction between N-C-N bridged Cu(II) centers. Magnetic exchange interactions (J’s) are also discussed on the basis of a computational study using DFT methodology. The spin density distribution (singlet ground state) is calculated to visualize the effect of delocalization of spin density through bridging groups.     

Carbonyl compound dependent hydrolysis of mono-condensed Schiff bases: A trinuclear Schiff base complex and a mononuclear mixed-ligand ternary complex of copper(II)

Two Schiff bases, HL¹ and HL² have been prepared by the condensation of N-methyl-1,3-propanediamine (mpn) with salicylaldehyde and 1-benzoylacetone (Hbn) respectively. HL¹ on reaction with Cu(ClO₄)₂·6H₂O in methanol produced a trinuclear Cu^II complex, [(CuL¹)₃(μ₃-OH)](ClO₄)₂·H₂O·0.5CH₂Cl₂ (1) but HL² underwent hydrolysis under similar reaction conditions to result in a ternary Cu^II complex, [Cu(bn)(mpn)ClO₄]. Both complexes have been characterised by single-crystal X-ray analyses, IR and UV-Vis spectroscopy and electrochemical studies. The partial cubane core [Cu₃O₄] of 1 consists of a central μ₃-OH and three peripheral phenoxo bridges from the Schiff base. All three copper atoms of the trinuclear unit are five-coordinate with a distorted square-pyramidal geometry. The ternary complex 2 is mononuclear with the square-pyramidal Cu^II coordinated by a chelating bidentate diamine (mpn) and a benzoylacetonate (bn) moiety in the equatorial plane and one of the oxygen atoms of perchlorate in an axial position. The results show that the Schiff base (HL²) derived from 1-benzoylacetone is more prone to hydrolysis than that from salicylaldehyde (HL¹). Magnetic measurements of 1 have been performed in the 1.8-300 K temperature range. The experimental data clearly indicate antiferromagnetism in the complex. The best-fit parameters for complex 1 are g = 2.18(1) and J = −15.4(2) cm⁻¹.