Syntheses,structures, and magnetic properties of heterobimetallic complexes based on tetracyanometallic building blocks

Two tetracyanometalate building blocks, [Fe(5,5′-dmbipy)(CN)₄]^? (2) and [Fe(4,4′-dmbipy)(CN)₄]^? (3) (5,5′-dmbipy = 5,5′-dimethyl-2,2′-bipyridine; 4,4′-dmbipy = 4,4′-dimethyl-2,2′-bipyridine), and two cyano-bridged heterobimetallic complexes, [Cu₂(bpca)₂(H₂O)₂Fe₂(5,5′-dmbipy)₂(CN)₈] · 2[Cu(bpca)Fe(5,5′-dmbipy)(CN)₄] · 4H₂O (4) and [Cu(bpca)Fe(4,4′-dmbipy)(CN)₄]_n (5) (bpca = bis(2-pyridylcarbonyl)amidate), have been synthesized and structurally characterized. Complex 4 contains two dinuclear and one tetranuclear heterobimetallic clusters in an asymmetric unit whereas the structure of complex 5 features a one-dimensional heterobimetallic zigzag chain. The Cu(II) ion is penta-coordinated in the form of a distorted square-based pyramid. Magnetic studies show ferromagnetic coupling between Cu(II) and Fe(III) ions with g = 2.28, J₁ = 2.64 cm^?1, J₂ = 5.40 cm^?1 and TIP = ?2.36 × 10^?3 for complex 4, and g = 2.17, J = 4.82 cm^?1 and zJ′ = 0.029 cm^?1 for complex 5.     

Effect of ligand congeniality on energy transfer reaction between photo-excited tris(bipyridine)ruthenium(II) and chromate(III) complexes in aqueous solutions

Energy-transfer rate-constants from photo-excited [Ru(N–N)₃]²⁺ (N–N = 2,2′-bipyridine (bpy), 4,4′-dimethyl-2,2′-bipyridine (4dmb), 5,5′-dimethyl-2,2′-bipyridine (5dmb)) to [Cr(O–O)₃]³⁻ (O–O²⁻ = ox²⁻ ((COO⁻)₂), mal²⁻ (CH₂(COO⁻)₂)) and [Cr(CN)₆]³⁻ in encounter complexes were evaluated in aqueous solutions containing alkali metal ion. The rate constant depends on the molecular size of the ruthenium(II) complex: 1.8 × 10⁸ s⁻¹ for [Ru(bpy)₃]²⁺ (molecular radius, r = 5.8 Å), 1.4 × 10⁸ s⁻¹ for [Ru(5dmb)₃]²⁺ (r = 6.1 Å) and 0.96 × 10⁸ s⁻¹ for [Ru(4dmb)₃]²⁺ (r = 6.7 Å) in the system of [Ru(N–N)₃]²⁺–[Cr(ox)₃]³⁻ in aqueous solution. However, the rate constant is much more sensitive to the chromate(III) complex than to ruthenium(II) complex; 1.8 × 10⁸ s⁻¹ and 0.43 × 10⁸ s⁻¹ for [Cr(ox)₃]³⁻ (r = 4.0 Å) and [Cr(mal)₃]³⁻ (r = 4.2 Å) in the [Ru(bpy)₃]²⁺–[Cr(O–O)₃]³⁻ systems, respectively. We conclude that the congeniality between the donor’s and acceptor’s ligands in encounter complex plays an important role in energy transfer in aqueous solution.     

Expanding the 4,4′-bipyridine ligand: Structural variation in {M(pytpy)2}2+ complexes (pytpy = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine,M = Fe,Ni, Ru) and assembly of the hydrogen-bonded,one-dimensional polymer {[Ru(pytpy)(Hpytpy)]}n3n+

The solid state structures of [Ni(1)₂][NO₃]₂ · 2MeOH · 2H₂O, [Fe(1)₂][ClO₄]₂ · 2MeOH · 0.5H₂O, [Ru(1)₂][PF₆]₂ and [Ru(1)₂][PF₆][NO₃] (1 = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine) are presented and the structural variation observed for the {M(1)₂}²⁺ unit is discussed. Protonation of the pendant pyridine group in [Ru(1)₂]²⁺ leads to the formation of a hydrogen-bonded, one-dimensional polymer [{Ru(1)(H1)}_n]³ⁿ⁺ exemplifed by the solid-state structure of [{Ru(1)(H1)}{Fe(NCS)₆} · 1.25H₂O]_n.     

Synthesis,crystal structure and magnetic properties of the spin crossover system [Fe(pq)3]2+

Three new compounds formulated (ClO₄)₂[Fe(pq)₃] (1), (BF₄)₂[Fe(pq)₃] · EtOH (2) and {(ClO₄)[MnCr(C₂O₄)₃][Fe(pq)₂(H₂O)₂]} (3), where pq is 2,2′-pyridylquinoline, have been synthesised and characterised. Despite the different crystal packing exhibited by 1 and 2, the cationic species [Fe(pq)₃]²⁺ are structurally quite similar. At 293 K, the Fe–N bond lengths are characteristic of the iron(II) in the high-spin state. In contrast to 1, 2 undergoes a continuous spin transition. Indeed, at 95 K its structure experiences a noticeable change in the Fe–N bonds and angles, i.e. the Fe–N bonds shorten by 0.194 Å on the average. The magnetic behaviour confirms that 1 is fully high-spin in the 4–300 K temperature range while 2 shows a spin transition centred at T_1/2 = 150 K. The corresponding enthalpy, entropy and interaction parameter are ΔH = 7.49 kJ mol^?1, ΔS = 50 J K^?1 mol^?1and Γ = 1.35 kJ mol^?1. Compound 3 has been obtained as a microcrystalline powder. The magnetic properties of 3 point at the occurrence of ferromagnetic coupling below 100 K and the onset of a ferromagnetic ordering below 10 K (Weiss constant equal to 6.8 K). The Mössbauer spectra of 3 show the occurrence of a magnetic order at T ? 4.2 K.     

Application of liquid chromatography-tandem mass spectrometry (LC–MS/MS) for the analysis of stable isotope enrichments of phenylalanine and tyrosine

Whole-body protein synthesis and breakdown are measured by a combined tracer infusion protocol with the stable isotope amino acids l-[ring-²H₅]-phenylalanine, l-[ring-²H₂]-tyrosine and l-[ring-²H₄]-tyrosine that enable the measurement of the phenylalanine to tyrosine conversion rate. We describe a liquid chromatography–tandem mass spectrometry (LC–MS/MS) method for the measurement of very low tracer–tracee ratios (TTR) of the amino acids l-phenylalanine and l-tyrosine in human plasma. TTR calibration curves of the tracers l-[ring-²H₅]-phenylalanine, l-[ring-²H₂]-tyrosine and l-[ring-²H₄]-tyrosine were linear (r² > 0.99) in the range between 0.01% and 5.0% TTR and lowest measurable TTR for the tracers was 0.01% at a physiological concentration of 60 μM. The method was applied successfully to plasma samples from a clinical study reaching a steady state enrichment plateau (mean ± SD) of 3.33 ± 0.19% for l-[ring-²H₅]-phenylalanine, 2.40 ± 0.43% for l-[ring-²H₂]-tyrosine and 0.29 ± 0.07% for l-[ring-²H₄]-tyrosine, respectively. The LC–MS/MS method can be applied for measurement of very low plasma enrichments of phenylalanine and tyrosine for the determination of whole-body protein synthesis and breakdown rates in humans.     

Linkage isomerism in the metal complex hexa(thiocyanato)rhenate(IV): Synthesis and crystal structure of (NBu4)2[Re(NCS)6] and [Zn(NO3)(Me2phen)2]2[Re(NCS)5(SCN)]

The linkage isomers [Re(NCS)₆]^2? and [Re(NCS)₅(SCN)]^2? are obtained by the reaction of [ReBr₆]^2? with NCS^? in dimethylformamide. Some differences in the chemical behavior allowed their separation and structural characterization in the form of (NBu₄)₂[Re(NCS)₆] (1) and [Zn(NO₃)(Me₂phen)₂]₂[Re(NCS)₅(SCN)] (2), respectively (Bu = n-C₄H₉ and Me₂phen = 2,9-dimethyl-1,10-phenanthroline).     

Diverse magnetic and electrical properties of molecular solids containing the thiazyl radical BDTA

We have examined the crystal structures and the electrical and magnetic properties of the molecular compounds of a thiazyl radical, 1,3,2-benzodithiazolyl (abbreviated as BDTA). BDTA was found to be a useful building block for molecular conductors and magnets because it can operate as a counter cation, a donor or a ligand, depending on its charge. (i) A charge-transfer complex, [BDTA][TCNQ], crystallizes into a uniform segregated stacking structure with a short contact between the donor and acceptor columns. In spite of the partial charge transfer between the two components, this complex exhibits semiconductive behaviour, probably due to a large electron correlation on BDTA. (ii) The crystal structure of [BDTA][Ni(mnt)₂] (mnt = maleonitriledithiolate) consists of alternating stacking columns of S = 0 [BDTA]⁺ and S = 1/2 [Ni(mnt)₂]^?, in which a ferromagnetic coupling operates between the [Ni(mnt)₂]^? anions through the [BDTA] ⁺ cation. (iii) [BDTA]₂[Cu(mnt)₂] consists of an alternating stack of a head-to-head [BDTA]⁺ dimer and a planar [Cu(mnt)₂]^2? dianion. Short intermolecular S?S contacts between the stacks give rise to an ideal 1D Heisenberg antiferromagnetic chain of [Cu(mnt)₂]^2? with a coupling constant of J/k_B = 16–17 K. (iv) The crystal structure of [BDTA]₂[Co(mnt)₂] is similar to that of [BDTA]₂[Cu(mnt)₂] at 253 K, but this salt undergoes a phase transition at 190 K, below which a partial electron transfer occurs from [Co(mnt)₂]^2? to one of the [BDTA]⁺ cations along with formation of a coordination bond. (v) [BDTA][Ni(dmit)₂]₂ (dmit = 1,3-dithiol-2-thione-4,5-dithiolate) exhibits room-temperature conductivity of 0.1 S cm^?1 and semiconductive behaviour over the range 80–200 K, which can be interpreted in terms of multi-conducting bands.     

Trispyrazolylmethane piano stool complexes of iron(II) and cobalt(II)

A series of cationic trispyrazolylmethane complexes of the general form [Tm^RM(CH₃CN)₃]²⁺ (Tm = tris(pyrazolyl)methane, 1, R = 3,5-Me₂, M = Fe(II); 2, R = 3-Ph, M = Fe(II); 3, R = 3,5-Me₂, M = Co(II); 4, R = 3-Ph, M = Co(II)) with ‘piano-stool’ structures was prepared by the reaction of the N₃tripodal ligands (Tm^R)with [(CH₃CN)₆M](BF₄)₂ in a 1:1 stoichiometric ratio. Magnetic susceptibility measurements indicate that all four complexes with BF₄⁻ counter anions are paramagnetic, high-spin systems in the solid state with μ_eff at high temperatures of 5.2 (1, S = 2), 5.4 (2, S = 2), 4.9 (3, S = 3/2) and 4.6 (4, S = 3/2) BM, respectively. Comparisons of bond lengths from the metal centre to the Tm^R nitrogen donors, and from the metal centre to the acetonitrile nitrogen donors indicate that the neutral tripodal ligands appear to be more weakly coordinated to the metal centre than are the acetonitrile ligands. Reactions of these tripodal complexes with bidentate phosphine ligands, such as 1,2-diphosphinoethane or 1,2-bis(diallylphosphino)ethane leads to displacement of the tripodal ligand, or to the formation of more thermally stable bis-ligand complexes M(Tm^R)₂ (R = 3,5-dimethyl).     

[Lys(DOTA)4]BVD15, a novel and potent neuropeptide Y analog designed for Y1 receptor-targeted breast tumor imaging

We substituted a truncated neuropeptide Y (NPY) analog, [Pro³⁰, Tyr³², Leu³⁴]NPY(28-36)NH₂ also called BVD15, at various positions with DOTA (1,4,7,10-tetraazacyclododecane-1,4,7-10-tetraacetic acid) and evaluated the effect of the coupling position with the binding affinity for NPY Y₁ receptors (NPY1R). Our data suggest that [Lys(DOTA)⁴]BVD15 (K_i = 63 ± 25 nM vs. K_i = 39 ± 34 nM for BVD15) is a potent NPY analog suitable for radiolabeling with metallo positron emitters for PET imaging of breast cancer.     

Two new N-heterocyclic carbene silver(I) complexes with the π–π stacking interactions

The precursors bis[N-(alkyl)benzimidazoliumylmethyl]durene halide (1a: alkyl = C₂H₅, halide = Br^?; 1b: alkyl = n-C₄H₉, halide = Cl^?; durene = 1,2,4,5-tetramethylbenzene) and their two new NHC silver(I) complexes [Durene(CH₂BimyEtAgBr)₂] (2a) and [Durene(CH₂BimyⁿBuAgCl)₂] (2b) (Bimy = benzimidazol-2-ylidene) have been prepared and characterized. In the crystal structures of 2a and 2b the aromatic π–π stacking interactions are observed.     

Synthesis of water-soluble dinuclear metal complexes [metal = cobalt(II) and nickel(II)] and their behavior in solution

Two dinuclear metal complexes, [Co₂(bhmp)(MeCO₂)₂]ClO₄ · 2H₂O (1) and [Ni₂(bhmp)(MeCO₂)₂]ClO₄ · 2H₂O (2), were synthesized with a dinucleating ligand, 2,6-bis[bis(2-hydroxyethyl)aminomethyl]-4-methylphenol [H(bhmp)]. Both complexes were easily soluble in water as well as in DMF. Electronic spectra for both complexes were measured in both solvents and analyzed using the angular overlap model (AOM). From the electronic spectra and molar conductance, both complexes were determined to exist as [M₂(bhmp)(MeCO₂)₂]⁺ (M = Co^II or Ni^II) in DMF, dissociating perchlorate ions. On the other hand, in water, it was concluded that the acetate ions were partially dissociated and each complex existed as a mixture of some dissociated species, such as [M₂(bhmp)(MeCO₂)(H₂O)₂]²⁺ and [M₂(bhmp)(H₂O)₄]³⁺ (M = Co^II or Ni^II). Such dissociation was also confirmed by precipitation of the dissociated species when NaBPh₄ was added into an aqueous solution of the nickel complex.     

Stress-induced dissociations between intracellular calcium signaling and insulin secretion in pancreatic islets

In healthy pancreatic islets, glucose-stimulated changes in intracellular calcium ([Ca²⁺]_i) provide a reasonable reflection of the patterns and relative amounts of insulin secretion. We report that [Ca²⁺]_i in islets under stress, however, dissociates with insulin release in different ways for different stressors. Islets were exposed for 48 h to a variety of stressors: cytokines (low-grade inflammation), 28 mM glucose (28G, glucotoxicity), free fatty acids (FFAs, lipotoxicity), thapsigargin (ER stress), or rotenone (mitochondrial stress). We then measured [Ca²⁺]_i and insulin release in parallel studies. Islets exposed to all stressors except rotenone displayed significantly elevated [Ca²⁺]_i in low glucose, however, increased insulin secretion was only observed for 28G due to increased nifedipine-sensitive calcium-channel flux. Following 3–11 mM glucose stimulation, all stressors substantially reduced the peak glucose-stimulated [Ca²⁺]_i response (first phase). Thapsigargin and cytokines also substantially impacted aspects of calcium influx and ER calcium handling. Stressors did not significantly impact insulin secretion in 11 mM glucose for any stressor, although FFAs showed a borderline reduction, which contributed to a significant decrease in the stimulation index (11:3 mM glucose) observed for FFAs and also for 28G. We also clamped [Ca²⁺]_i using 30 mM KCl + 250 μM diazoxide to test the amplifying pathway. Only rotenone-treated islets showed a robust increase in 3–11 mM glucose-stimulated insulin secretion under clamped conditions, suggesting that low-level mitochondrial stress might activate the metabolic amplifying pathway. We conclude that different stressors dissociate [Ca²⁺]_i from insulin secretion differently: ER stressors (thapsigargin, cytokines) primarily affect [Ca²⁺]_i but not conventional insulin secretion and ‘metabolic’ stressors (FFAs, 28G, rotenone) impacted insulin secretion.     

Synthesis,spectral and magnetical characterization of monomeric [Cu(2-NO2bz)2(3-pyme)2(H2O)2] and polymeric [Cu{3,5-(NO2)2bz}2(3-pyme)2]n

Two new complexes of composition [Cu(2-NO₂bz)₂(3-pyme)₂(H₂O)₂] (1) and/or [Cu{3,5-(NO₂)₂bz}₂(3-pyme)₂] (2) (3-pyme = 3-pyridylmethanol, ronicol or 3-pyridylcarbinol, 2-NO₂bz = 2-nitrobenzoate and 3,5-(NO₂)₂bz = 3,5-dinitrobenzoate) have been prepared and studied by elemental analysis, electronic, infrared and EPR spectroscopy, magnetic susceptibility measurements and the structure of both complexes has been solved. Complex (1) shows an unusual molecular type of structure consisting of the [Cu(2-NO₂bz)₂(3-pyme)₂(H₂O)₂] molecules held together by hydrogen bonds and van der Waals interactions. Complex (2) exhibits a polymeric chain-like structure [Cu{3,5-(NO₂)₂bz}₂(3-pyme)₂]_n with copper atoms doubly bridged by two 3-pyridylmethanol molecules and the polymeric molecules are held together by van der Waals interactions. Complex (1) exhibits a magnetic moment μ_eff = 1.84 B.M. at 300 K that remains nearly constant within the temperature region (5–300 K). Further cooling results in lowering the magnetic moment to μ_eff = 1.82 B.M. at 1.8 K. The magnetic susceptibility temperature dependence obeys Curie–Weiss law with Curie constant of 0.423 cm³ K mol⁻¹ and with Weiss constant of −0.06 K. The magnetic moment of (2) exhibits a small increase with a decrease in the temperature (μ_eff = 1.80 B.M. at 300 K and μ_eff = 1.85 B.M. at 1.8 K) with Curie constant of 0.409 cm³ K mol⁻¹ and with Weiss constant of +1.1 K, which can indicate a very weak ferromagnetic interaction between the copper atoms within the chain. Applying the molecular field model resulted in obtaining zJ′ values −0.08 cm⁻¹ for complex (1), and −0.07 cm⁻¹ for complex (2), respectively, that could characterize intermolecular and interchain interactions transmitted through π–π stacking.     

Synthesis of metal dithiolene complexes by Si–S bond cleavage of a bis(silanylsulfanyl)alkene

A new method for the synthesis of metal dithiolenes with alkyl-substituted chelate rings has been investigated. The utility of the protected ene-1,2-dithiolate 3,4-bis-triisopropylsilanyl-sulfanyl-hex-3-ene as a precursor in reactions with metal halide and oxyhalide complexes was examined. Reaction conditions involve a 2:1 or 3:1 mol ratio of reactants in acetonitrile/THF or toluene at 50–80 °C for 24–36 h. Complex formation was observed as a result of Si–S bond cleavage by bound or free halide and oxo ligands. Members of four major structural families of dithiolene complexes were prepared in ca. 25–70% yields, including planar [Ni(S₂C₂Et₂)₂], square pyramidal [MI(S₂C₂Et₂)₂] (M = Co, Fe), [Fe(py)(S₂C₂Et₂)₂]¹⁻, and [ReO(S₂C₂Et₂)₂]¹⁻, centrosymmetric [M₂(S₂C₂Et₂)₄]²⁻ (M = Co, Mn), [M(S₂C₂Et₂)₃]¹⁻ (M = V, Nb), and trigonal prismatic [M(S₂C₂Et₂)₃] (M = Mo, W). Seven X-ray structure proofs are provided. It is concluded that the method is feasible and potentially extendable to other ring substituents, whose primary effects are on solubility and modulation of redox potentials.     

Synthesis of new palladium(II) complexes containing tetradentate-nitrogen donor ligands: Combined structural studies by NMR spectroscopy and X-ray crystallography

Treatment of the tetradentate (NN′N′N) N-alkylaminopyrazole ligands 3,6-dimethyl-1,8-(3,5-dimethyl-1-pyrazolyl)-3,6-diazaoctane (ddad) and 1,4-bis[2-(3,5-dimethyl-1-pyrazolyl)ethyl]piperazine (bedp) with [PdCl₂(CH₃CN)₂] in a 1:1 M/L ratio in acetonitrile produces [Pd₂Cl₄(L)] and [PdCl₂(L)] (L = ddad and bedp). Treatment of the corresponding complex [PdCl₂(L)] (L = ddad, bedp) in the presence of AgBF₄ in CH₂Cl₂/methanol (2:1) or NaBF₄ in acetonitrile gives [Pd(L)](BF₄)₂. The Pd(II) complexes have been characterised by elemental analyses, conductivity measurements, IR and ¹H and ¹³C{¹H} NMR spectroscopies when possible. The X-ray structure of the complex [Pd(ddad)]Cl₂ · 3H₂O has been determined. The Pd(II) is coordinated to the ddad ligand by two nitrogen atoms of pyrazolyl groups and two nitrogen atoms of the amine groups, in a slightly distorted square-planar geometry.     

A multifrequency high-field EPR (9–285 GHz) investigation of a series of dichloride mononuclear penta-coordinated Mn(II) complexes

The electronic structure of a series of 11 penta-coordinated dichloride mononuclear Mn(II) complexes [Mn(L)Cl₂] (L = Cl-terpy, Br-terpy, OH-terpy, phenyl-terpy, tolyl-terpy, mesityl-terpy, EtO-terpy, Me₂N-terpy, tBu₃-terpy, py-phen, and dpya) has been investigated by a multifrequency EPR study (9–285 GHz). The X-ray structures of [Mn(Br-terpy)Cl₂], [Mn(EtO-terpy)Cl₂], [Mn(Me₂N-terpy)Cl₂] and [Mn(tolyl-terpy)Cl₂] are described. The spin Hamiltonian parameters have been determined for all complexes and show that the steric and electronic effects of the N-tridentate ligand L do not induce appreciable variations on the zero field splitting parameters. The magnitude of D, close to 0.3 cm⁻¹, is governed by the chloride anion. High-field EPR spectroscopy allows the determination of electronic parameters of mononuclear Mn(II) complexes characterized by relatively large magnitudes of D and the unambiguous interpretation of the X-band spectra of these kinds of complexes.     

Profiling oestrogens and testosterone in human urine by stable isotope dilution/benchtop gas chromatography–mass spectrometry

Oestrogens, such as oestrone (E₁), 17β-oestradiol (E₂), oestriol (E₃) and their biologically active metabolites 2-methoxyoestrone (2-MeOE₁), 2-hydroxyoestradiol (2-OHE₂) 16-ketooestradiol (16-OE₂), 16-epioestriol (16-epiE₃), as well as testosterone (T) play an important role in physiological and pathological developmental processes during human development. We therefore aimed at developing an isotope dilution/bench top gas chromatography–mass spectrometry (ID/GC–MS) method, based on benchtop GC–MS, for the simultaneous determination (‘profiling’) of the above analytes in children. The method consisted of equilibration of urine (5 ml) with a cocktail containing stable isotope-labelled analogues of the analytes as internal standards ([2,4-²H₂]E₁, [2,4,16,16-²H₄]E₂, [2,4,17-²H₃]E₃, [16,16,17-²H₃]T, [1,4,16,16-²H₄]2-MeOE₁, [1,4,16,16,17-²H₅]2-OHE₂, [2,4,15,15,17-²H₅]16-OE₂ and [2,4-²H₂]16-epiE₃). Then, solid-phase extraction (C₁₈ cartridges), enzymatic hydrolysis (sulphatase from Helix pomatia (type H-1)), re-extraction, purification by anion exchange chromatography and derivatisation to trimethylsilyl ethers followed. The samples were analysed by GC–MS (Agilent GC 6890N/5975MSD; fused silica capillary column 25 m × 0.2 mm i.d., film 0.10 μm). Calibration plots were linear and showed excellent reproducibility with coefficients of determination (r²) between 0.999 and 1.000. Intra- and inter-assay coefficients of variation (CV) were <2.21% for all quantified metabolites. Sensitivity was highest for 2-OHE₂ (0.25 pg per absolute injection: signal-to-noise ratio (S/N) = 3) and lowest for 16-epiE₃ (2 pg per absolute injection: S/N = 2.6), translating into corresponding urine sample analyte concentrations of 0.025 ng ml^?1 and 0.2 ng ml^?1, respectively. Accuracy – determined in a two-level spike experiment – showed relative errors ranging between 0.15% for 16-OE₂ and 11.63% for 2-OHE₂. Chromatography showed clear peak shapes for the components analysed. In summary, we describe a practical, sensitive and specific ID/GC–MS assay capable of profiling the above-mentioned steroids in human urine from childhood onwards.     

Origin of magnetization tunneling in single-molecule magnets as determined by single-crystal high-frequency EPR

We review an extensive body of single-crystal high-frequency electron paramagnetic resonance (HFEPR) data in order to determine the transverse spin Hamiltonian parameters that control the tunneling of the direction of magnetization in a variety of integer and half-integer-spin single-molecule magnets (SMMs). The SMMs studied are members of the following families: S = 9/2 [Mn₄O₃Cl]⁶⁺; S = 5 [Mn₃NiO₄]⁶⁺; S = 6 [Mn₃ZnO₄]⁶⁺; and S = 4 [Ni₄(OR)₄]⁴⁺. HFEPR spectra for the half-integer S = 9/2 Mn₄ complexes that have C₃ symmetry do not provide measurable evidence for transverse spin Hamiltonian terms. This finding is consistent with the relatively large coercive field seen in the magnetization hysteresis loops for these complexes. On the other hand, a low symmetry S = 9/2 complex exhibits a much faster rate of ground-state magnetization tunneling, in agreement with HFEPR spectra for a powder sample that gives a rhombic zero-field splitting (ZFS) parameter of E = 0.140 cm^?1. The S = 5 Mn₃Ni systems exhibit magnetization tunneling that is much faster than seen for the high-symmetry S = 9/2 Mn₄ complexes. This can be attributed to their integer-spin ground states. Like the C₃ symmetry Mn₄ SMMs, the HFEPR spectra for high-symmetry Mn₃Ni complexes do not provide measurable evidence for transverse ZFS terms. However, the spectra exhibit broad peaks, suggesting distributions in the local molecular environments brought about by disordered solvate molecules. This disorder likely explains the fast tunneling in the high-symmetry S = 5 Mn₃Ni systems, though one cannot rule out fourth- (and higher-) order interactions that cannot be detected by HFEPR due to the broad resonances. The one S = 6 Mn₃Zn complex shows an even faster rate of tunneling compared to the isostructural S = 5 Mn₃Ni complex. Finally, the S = 4 [Ni(hmp)(dmb)Cl]₄ complex provides unique insights into the origin of fourth- (and higher-) order interactions found for many SMMs on the basis of analysis using a giant spin Hamiltonian (GSH) approximation. We conclude that the fourth-order anisotropy found for the S = 4 ground state of [Ni(hmp)(dmb)Cl]₄ originates from the second-order ZFS interactions associated with the individual Ni^II ions, but only as a result of higher-order processes that occur via S-mixing between the ground state and higher-lying (S < 4) spin-multiplets. The S-mixing is relatively strong in this system because of comparable exchange and anisotropy energy scales. The relatively fast tunneling is a direct consequence of this S-mixing, as opposed to any intrinsic fourth-order (spin–orbit) anisotropy associated with Ni^II.     

Crystal structure,magnetic and thermal properties of the one-dimensional complex [Nd(pzam)3(H2O)Mo(CN)8] · H2O

The new d–f cyanido-bridged 1D assembly [Nd(pzam)₃(H₂O)Mo(CN)₈] · H₂O was prepared by self-assembly of pyrazine-2-carboxamide (pzam), Nd(NO₃) · nH₂O and (Bu₃NH)₃[Mo(CN)₈] · 4H₂O in acetonitrile. X-ray crystallographic studies indicate that the complex comprises chains of alternating, cyanido-bridged [Nd(pzam)₃(H₂O)]³⁺ and Mo(CN)₈]^3? fragments. The magneto-structural properties have been studied by field-dependent magnetization and specific heat measurements at low temperatures (?0.3 K). Below ≈10 K the Nd(III) moment is well approximated by an effective spin S = 1/2, with anisotropic g-tensor. The exchange coupling between the Nd(III) and the Mo(V) spins S = 1/2 along the structural chains is found to be ferromagnetic, with J/k_B = 1.8 ± 0.2 K and approximately XY (planar) anisotropy. No evidence for 3D interchain magnetic ordering is found. A comparison with magneto-structural data of other cyanido-bridged complexes involving the Nd(III) ion is presented.     

Acetato complexes of molybdenum(V): A novel tetranuclear core based on the metal–metal bonded {Mo2O4}2+ units

A series of acetato complexes of molybdenum(V), based on the singly metal–metal bonded {Mo₂O₄}²⁺ structural fragment, has been prepared. A dinuclear (PyH)₃[Mo₂O₄Cl₄(OOCCH₃)] · CH₃CN (1) (PyH⁺ = pyridinium cation, C₅H₅NH⁺) was obtained upon the reaction of (PyH)₅[MoOCl₄(H₂O)]₃Cl₂ with the equimolar solution of pyridine and acetic acid in acetonitrile at ambient conditions. The acetato ligand in 1 is coordinated to a pair of molybdenum atoms in a syn–syn bidentate bridging manner. (PyH)_n[MoOBr₄]_n afforded in an analogous synthetic procedure a tetranuclear cluster, [Mo₄O₈(OOCCH₃)₃(OH)Py₄] · 1/2CH ₃CN · 1/2H₂O (3), with a novel core which may be envisioned as the acetate- and hydroxide-assisted assembly of {Mo₂O₄}²⁺ building blocks. Its structure is presented in terms of known tetranuclear clusters which are also composed of two {Mo₂O₄}²⁺ units. The acetato ligands in 3 adopted apart from bidentate bridging binding modes also a monodentate one. Partial substitution of chlorido ligands in (PyH)₃[Mo₂O₄Cl₄(OOCCH₃)] · CH₃CN (1) with pyridine resulted in a neutral [Mo₂O₄Cl(OOCCH₃)Py₃] · PrⁱOH · Py (2) which retained the original acetate coordination. The title compounds were fully characterized by X-ray diffraction studies and infrared vibrational spectroscopy.