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Six new anionic bismuth-oxido clusters containing trifluoroacetate ligands were prepared. These include two new Bi6O8 clusters: [M(NCMe)2(H2O)4]3[Bi6(μ3-O)4(μ3-OH)4(CF3CO2)12] with an octahedral Bi6O4(OH)4 core (M = Ni, 1a; Co, 1b) and four Bi4O2 clusters, {[Co(NCMe)6][Bi4(μ3-O)2(CF3CO2)10]}n (2a), {[Co{HC(MeCO)2(MeCNH)}2][Bi4(μ3-O)2(CF3CO2)10]·2[CF3CO2]·2[CF3CO2H]·2[H2O]}n (2b), {[Cu(NCMe)4]2[Bi4(μ3-O)2(CF3CO2)10]·2[CF3CO2H]}n (2c), and {[Me4N]2[Bi4(μ3-O)2(CF3CO2)10]·2[CF3CO2H]}n (2d). These are among the first bismuth-oxido anionic clusters synthesized, and the first to have transition metal countercations. The Bi6O8 anion in 1a and 1b is a high-symmetry octahedron. Additionally, two of the new Bi4O2 clusters are arranged in 1D polymeric structures via bridging carboxylate ligands. The cation in compound 2c had not been previously characterized and was also observed in the synthesis of [Co{HC(MeCO)2(MeCNH)}2][Bi(NO3)6] (3). The new compounds were characterized using single crystal X-ray crystallography ...

International audience; A series of clusters of the form [Et4N][Fe2(CO)6(μ3-As)}(μ3-EFe(CO)4)], where E is either P or As, were synthesized from [Et4N]2[HAs{Fe(CO)4}3] and ECl3. AsCl3 gives the As-only compound; PCl3 produces compounds having two As atoms with one P atom, or one As atom and two P atoms, and they can exist as two possible isomers, one of which is chiral. The As2P and AsP2 clusters cocrystallize, and their structure as determined by single-crystal X-ray diffraction is given along with the structure of the As-only cluster. Analytical data as well as density functional theory calculations support the formation and geometries of the new molecules.

Alkali metal cations can interact with Fe–N2 complexes, potentially enhancing back-bonding or influencing the geometry of the iron atom. These influences are relevant to large-scale N2 reduction by iron, such as in the FeMoco of nitrogenase and the alkali-promoted Haber–Bosch process. However, to our knowledge there have been no systematic studies of a large range of alkali metals regarding their influence on transition metal–dinitrogen complexes. In this work, we varied the alkali metal in [alkali cation]2[LFeNNFeL] complexes (L = bulky β-diketiminate ligand) through the size range from Na+ to K+, Rb+, and Cs+. The FeNNFe cores have similar Fe–N and N–N distances and N–N stretching frequencies despite the drastic change in alkali metal cation size. The two diketiminates twist relative to one another, with larger dihedral angles accommodating the larger cations. In order to explain why the twisting has so little influence on the core, we performed density functional theory calculations on a simplified LFeNNFeL model, which show that the two metals surprisingly do not compete for back-bonding to the same π* orbital of N2, even when the ligand planes are parallel. This diiron system can tolerate distortion of the ligand planes through compensating orbital energy changes, and thus, a range of ligand orientations can give very similar energies., We describe a series of diketiminate-supported FeNNFe complexes in the formal Fe0 oxidation state, which have two alkali metal cations (alkali metal cation = Na+, K+, Rb+, Cs+) bound side-on to the N2 ligand. Larger cations twist the core of the molecule, but the back-bonding is similar through the series. Computations on the FeNNFe core show that the orbital energies move in compensating directions upon twisting, explaining the curious independence of the core metrics with twisting.

Here, we describe the synthesis of the single amino acid chelator DOTAlaP and four of its derivatives. The corresponding gadolinium(III) complexes were investigated for their kinetic inertness, relaxometric properties at a range of fields and temperatures, water exchange rate, and interaction with human serum albumin (HSA). Derivatives with one inner-sphere water (q = 1) were determined to have a mean water residency time between 8 and 6 ns in phoshate-buffered saline at 37 °C. The corresponding europium complexes were also formed and used to obtain information on the hydration number of the corresponding coordination complexes. Two complexes capable of binding HSA were also synthesized, of which one, Gd(5b), contains no inner-sphere water, while the other derivative, Gd(4b), is a mixture of ca. 15% q =1 and 85% q = 0. In the presence of HSA, the latter displayed a very short mean water residency time (τM310 = 2.4 ns) and enhanced relaxivity at intermediate and high fields. The kinetic inertness of Gd(4b) with respect to complex dissociation was decreased compared to its DOTAla analogue but still 100-fold more inert than [Gd(BOPTA)(H2O)]2–. Magnetic resonance imaging in mice showed that Gd(4b) was able to provide 38% better vessel to muscle contrast compared to the clinically used HSA binding agent MS-325., Converting one of the acetate groups in the single amino acid chelator DOTAla to methylenephosphonate (DOTAlaP) results in gadolinium(III) complexes with extremely fast water exchange kinetics and/or in equilibrium between monoaquated (q = 1) and unaquated (q = 0) states. The presence of phosphonate and the very fast water exchange kinetics result in stable complexes with high relaxivity at high magnetic fields, especially when bound to serum albumin.

Heme is emerging as a key player in the synchrony of circadian-coupled transcriptional regulation. Current evidence suggests that levels of circadian-linked transcription are regulated in response to both the availability of intracellular heme and heme-based sensing of carbon monoxide (CO) and possibly nitric oxide (NO). The protein CLOCK is central to the regulation and maintenance of circadian rhythms in mammals. CLOCK comprises two PAS domains, each with a heme binding site. Our studies focus on the functionality of the murine CLOCK PAS-A domain (residues 103-265). We show that CLOCK PAS-A binds iron(III) protoporhyrin IX to form a complex with 1:1 stoichiometry. Optical absorbance and resonance Raman studies reveal that the heme of ferric CLOCK PAS-A is a six-coordinate, low-spin complex whose resonance Raman signature is insensitive to pH over the range of protein stability. Ferrous CLOCK PAS-A is a mixture of five-coordinate, high-spin and six-coordinate, low-spin complexes. Ferrous CLOCK PAS-A forms complexes with CO and NO. Ferric CLOCK PAS-A undergoes reductive nitrosylation in the presence of NO to generate a CLOCK PAS-A-NO, which is a five-coordinate {FeNO}(7) complex. Formation of the highly stable {FeNO}(7) heme complex from either ferrous or ferric heme makes possible the binding of NO at very low concentration, a characteristic of NO sensors. Comparison of the spectroscopic properties and CO-binding kinetics of CLOCK PAS-A with other CO sensor proteins reveals that CLOCK PAS-A exhibits chemical properties consistent with a heme-based gas sensor protein.

Heterometallic bismuth-niobium or -tantalum salicylate complexes react with sodium tetraphenylborate to produce complexes in which one or more aryl groups have been transferred from boron to bismuth with the concomitant displacement of a eta(2)-salicylato ligand. When the previously reported Bi(2)Ta(2)(sal)(4)(Hsal)(4)(OEt)(4) (1) and BiTa(4)(mu-O)(4)(sal)(4)(Hsal)(3)(O(i)Pr)(4) (2) are treated with an alcoholic solution of NaBPh(4), the compounds [PhBi(Hsal)Ta(sal)(2)(OEt)(2) x EtOH](2) (3) and PhBiTa(4)(mu-O)(4)(Hsal)(2)(sal)(4)(OEt)(4) x CH(2)Cl(2) (4) are produced (sal = O(2)CC(6)H(4)-2-O(2-), Hsal = O(2)CC(6)H(4)-2-OH(-)). The core geometries of the heterometallic complexes are retained. However, if preparations of compound 1 are treated with NaBPh(4) without prior isolation of 1, [Ph(2)BiNb(sal)(2)(OMe)(2)](infinity) (5) is produced instead. This compound was characterized both as a solvent-free crystalline form and as one containing a lattice diethyl ether. The compound exhibits a polymeric chain structure that can be viewed as alternating [Ph(2)Bi](+) and [Nb(sal)(2)(OMe)(2)](-) units connected via bridging carboxylate groups. The arylation of the bismuth(III) center proceeds smoothly under mild conditions at room temperature, affording a new means for the mild functionalization of bismuth-transition metal heterometallic complexes.

A recent report of the structural and vibrational properties of heme-bound HNO in myoglobin, MbHNO, revealed a long Fe-N H N O bond with the hydrogen atom bonded to the coordinated N atom. The Fe-N(H)-O moiety was reported to exhibit an unusually high Fe-N H N O stretching frequency relative to those of the corresponding {FeNO} 6 and {FeNO} 7 porphyrinates, despite the Fe-N H N O bond being longer than either of its Fe-N N O counterparts. Herein, we present results from density functional theory calculations of an active site model of MbHNO that support the previous assignment and clarify this seemingly contradictory result. The results are consistent with the experimental evidence for a ground-state Fe-N(H)-O structure having a long Fe-N H N O bond and a uniquely high ν F e - N ( H N O ) frequency. This high frequency is the result of the correspondingly low reduced mass of the normal mode, which is largely attributable to significant motion of the N-bound hydrogen atom. Additionally, the calculations show the Fe-N(H)O bonding in this complex to be remarkably insensitive to whether the HNO and ImH ligand planes are parallel or perpendicular. This is attributed to insensitivities of the Fe-L a x i a l characters of molecular orbitals to the relative HNO and ImH orientation in both the parallel and perpendicular conformers.

The reaction of a 1:2 mixture of bismuth(III) salicylate with titanium(IV) isopropoxide in refluxing toluene has been investigated and found to proceed with ligand exchange to produce the new heter...

Bismuth(III) salicylate, [Bi(Hsal)(3)](n), reacts readily with the trivalent metal beta-diketonate compounds M(acac)(3) (acac = acetylacetonate; M = Al, V, Cr, Fe, Co) to produce trinuclear coordination complexes of the general formula Bi(2)(Hsal)(6).M(acac)(3) (M = Al, V, Cr, Fe, Co) in 60-90% yields. Spectroscopic and single crystal X-ray diffraction experiments indicate that these complexes possess an unusual asymmetric nested structure in both solution and solid state. Upon standing in dichloromethane solution, Bi(2)(Hsal)(6).Co(acac)(3) eliminates Bi(Hsal)(3) to give the 1:1 adduct Bi(Hsal)(3).Co(acac)(3). The 2:1 heterobimetallic molecular compounds undergo facile thermal decomposition on heating in air to 475 degrees C to produce heterometallic oxide materials, which upon annealing for 2 h at 700 degrees C form crystalline oxide materials. The synthetic approach detailed here represents a unique, general approach to the formation of heterobimetallic bismuth-based coordination complexes via the coordination of M(acac)(3) complexes to bismuth(III) salicylate.

The ability of the transition metal complex M(salen)* (M = Ni, Cu) to form Lewis acid−base adducts with lead(II) salts has been explored. The new complexes Pb(Hsal)2(Cu(salen*))2 (1), {Pb(NO3)(Cu(salen*))2}(NO3) (2), Pb(OAc)2(Cu(salen*)) (3), and {Pb(OAc)(Ni(salen*)2}(OAc) (4) (Hsal = O2CC6H4-2-OH, salen* = bis(3-methoxy)salicylideneimine) have been synthesized and characterized spectroscopically and by single-crystal X-ray diffraction. The coordination environment of the lead in the heterobimetallic complex is sensitive both to the initial lead salt and to the transition metal salen complex that is employed in the synthesis. As a result, we have been able to access both 2:1 and 1:1 adducts by varying either the lead salt or the transition metal in the heterobimetallic coordination complex. In all cases, the salen* complex is associated with the lead center via dative interactions of the phenolic oxygen atoms. The relationship between the coordination requirements of the lead and the chemical nature of th...

Reactions between triphenyl bismuth, salicylic acid, and niobium or tantalum ethoxide have been explored. Four new coordination complexes incorporating bismuth and the group 5 metals niobium or tantalum have been synthesized and characterized spectroscopically, by elemental analysis, and by single crystal X-ray diffraction. The new complexes are Bi2M2(μ-O)(sal)4(Hsal)4(OEt)2 (1a, M = Nb; 1b, M = Ta) and BiM4(μ-O)4(sal)4(Hsal)3(OiPr)4 (sal = O2CC6H4-2-O, Hsal = O2CC6H4-2-OH) (2a, M = Nb; 2b, M = Ta). Complexes 1a and 1b are isomorphous, as are 2a and 2b. The thermal and hydrolytic decomposition of 1a has been explored by DT/TGA and powder X-ray diffraction, while scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) were used to characterize the morphology and composition of the oxides. The heterobimetallic molecules are completely converted to the amorphous bimetallic oxide by heating to 500 °C in air. Decomposition of 1a or 1b at 650 °C produces the metastable high temperature...

The reactions between triphenylbismuth, salicylic acid, and the metal alkoxides M(OCH2CH3)5 (M = Nb, Ta) or Ti{OCH(CH3)2}4 have been investigated under different reaction conditions and in differen...

Exposing [Bi(OR)3(toluene)]2 (1, R = OC6F5) to different solvents leads to the formation of larger polymetallic bismuth oxo alkoxides via ether elimination/oligomerization reactions. Three differen...

The synthesis and characterization of a series of meso-2-pyridylporphyrins and their Mg(2+) complexes are reported. Condensation of 4-alkylbenzyl-2,2'-dipyrromethanes (alkyl = Me, n-Pr, or n-Bu) with 2-pyridinecarboxaldehyde yielded a series of free-base meso-2-pyridylporphyrins. Insertion of Mg(2+) into the free-base porphyrins yielded the respective magnesium complexes. These compounds were characterized using 1D ((1)H and (13)C) and 2D ((1)H-(1)H COSY) NMR methods, UV-visible absorption spectroscopy, fluorescence spectroscopy, and mass spectrometry. The interplanar spacing of the dimers is sufficiently small that there is excitonic coupling of the constituent chromophores. The overall dissociation constant of these dimers is estimated at 2 x 10(-)(6) M. Addition of donor ligands such as acetone, DMF, DMSO, or pyridine converts the dimeric species to their respective constituent monomers. Titration of the dimeric complex with pyridine-d(5)() shows that disaggregation requires coordination of two pyridine molecules at independent binding sites. Tracking of the pyridine coordination by (1)H NMR spectroscopy allowed for determination of the equilibrium constant for the pyridine-induced disaggregation reaction (2.1 x 10(-)(3) M(2)). Both the spontaneous dissociation and the pyridine-induced disaggregation reactions occur by two steps.

A number of main group element (E)−transition metal (M) cluster compunds based upon a hexacapped M8 cube have been reported in two configurations: empty and with interstitial metal atoms in the center of the cube. Related molecules arise upon slow oxidation of the reaction product that forms when [Bi2Co4(CO)11]- is treated with Mo(CO)3(toluene) giving Bi−Co clusters based upon tetragonally distorted tetracapped cubic metal arrays with interstitial metal atoms. These compounds formulated as [PPN]2[Bi4Co9(CO)16]·2THF ([PPN]2[1]·2THF) and [PPN]2[Bi8Co14(CO)20]·1.08THF([PPN]2[2]·1.08THF) have been characterized via single-crystal X-ray diffraction. An alternative description ascribes the metal cores to close-packed arrays based upon the cuboctahedron. The complexes are electron rich via conventional electron-counting formalisms. To understand these molecules more fully, a thorough theoretical analysis of compounds [1]2- and [2]2- was undertaken. The calculations indicate that the bonding of the interstitial ...

The reaction of [Q]2[Bi4Fe4(CO)13] ([Q]2[1]; [Q] = [Et4N]+, [PhCH2NMe3]+) with MePCl2 in MeCN is a complicated reaction which gives different results depending upon the stoichiometry of the reaction. At a ratio of 1:1.33 (cluster:phosphine), the reaction yields a mixture of the new bismuth−iron carbonyl compounds [Q][(μ-H)Fe2(CO)6Bi2{Fe(CO)4}] ([Q][2]), which has a tetrahedral Fe2Bi2 core edge-bridged across the bismuth centers by an [Fe(CO)4]2- fragment, and [Q]3[Bi3Cl4(μ-Cl)4{Fe(CO)3}] ([Q]3[3]), containing a reduced complex ion [Bi3Cl8]- stabilized by coordination to an iron tricarbonyl fragment. Extended Huckel molecular orbital calculations on this unusual anion are consistent with each bismuth atom possessing the same reduced oxidation state of +2.33. The compound [Et4N][2] crystallizes in the triclinic space group P1 (No. 2) with a = 10.246(2) A, b = 11.859(2) A, c = 12.474(2) A, α = 71.11(3)°, β = 79.60(3)°, γ = 76.37(3)°, V = 1384.7(4) A3, and Z = 2, while [PhCH2NMe3]3[3]·0.87Et2O was characteri...

The reaction of [Bi(OR(f))(3).C(7)H(8)](2) (R(f) = C(6)F(5)) with sodium pentafluorophenolate leads to two new mixed-metal aryloxide complexes depending upon stoichiometry. Using 1 equiv of NaOR(f) per bismuth atom, a polymeric chain with the formula [NaBi(OC(6)F(5))(4)(THF)](infinity), 1, was isolated. If 2 equiv of NaOR(f) is used, the heterometallic oxo/aryloxide Na(4)Bi(2)(m(6)-O)(OC(6)F(5))(8)(THF)(4), 2, is formed. The mass spectroscopic data confirms the elimination of the bis(pentafluorophenyl) ether, R(f)OR(f), concomitant with oxo-ligand formation. The compounds have been characterized spectroscopically and by single-crystal X-ray diffraction: Compound 1 crystallizes in the chiral monoclinic space group P2(1), with a= 12.324(2) A, b = 10.934(2) A, c = 13.334(3) A, beta = 91.19(3) degrees, V = 1796.4(6) A(3), and Z = 2. The polymeric chain in 1 sits about the 2-fold screw axis and is the source of chirality for the compound. Compound 2 crystallizes in the triclinic space group Po, with a = 14.059(3) A, b = 14.060(3) A, c = 11.531(2) A, alpha = 108.47(3) degrees, beta = 102.78(3) degrees, gamma = 108.61(3) degrees, V=1912.6(7) A(3), and Z = 1 and shows occupational disorder of the sodium and bismuth atom positions. Variable-temperature (19)F-NMR studies show dynamic behavior of these bismuth aryloxide complexes in solution.

The pyrolysis of [NEt4]2[Bi4Fe4(CO)13] in MeCN cleanly produces the square-pyramidal cluster [NEt4]2[Fe3(CO)9Bi2]. An X-ray crystallographic study was carried out on this compound at 223 K (orthorh...