Sodium Aminodiboranates Na(H3BNR2BH3): Structural and Spectroscopic Studies of Steric and Electronic Substituent Effects.

We describe the syntheses of a series of sodium aminodiboranate salts, Na(H3B-NR2-BH3), with different substituents on nitrogen, including sodium salts of the unsubstituted aminodiboranate, H3B-NH2-BH3-, and of the N-substituted anions H3B-NRR'-BH3-, where NRR' = NHMe, NHEt, NH(SiMe3), NEt2, N(i-Pr)2, N(SiMe3)2, NMe(i-Pr), NMe(t-Bu), NMe(SiMe3), and the pyrrolidide and piperidide derivatives NC4H8, NC5H10, and NC5H8-cis-2,6-Me2. The compounds have been characterized by 1H and 11B NMR spectroscopy and IR spectroscopy; crystallographic studies have been carried out for the unsolvated N,N-dimethylaminodiboranate salt Na(H3B-NMe2-BH3) and several sodium aminodiboranate salts in which the sodium ions are solvated with ethers (dioxane, diglyme, tetrahydrofuran, and 12-crown-4) or amines (N,N,N',N'-tetramethylethylenediamine). One of the structures contains a rare example of an ether ligand in which one oxygen atom bridges between two metal ions. General structural and spectroscopic trends as a function of the substituents on nitrogen are discussed.

Pr(H3BNMe2BH3)3 and Pr(thd)3 as Volatile Carriers for Actinium-225. Deposition of Actinium-Doped Praseodymium Boride Thin Films for Potential Use in Brachytherapy.

Here we show that the praseodymium N,N-dimethylaminodiboranate complex Pr(H3BNMe2BH3)3 and the 2,2,6,6-tetramethylheptane-3,5-dionate complex Pr(thd)3 can serve as volatile carriers for 225Ac. The actinium coordination complexes Ac(H3BNMe2BH3)3 and Ac(thd)3 are the likely species subliming with the carrier material. A sample of 225Ac-doped Pr(H3BNMe2BH3)3 was used to deposit amorphous 225Ac-doped praseodymium boride films on glass and Si(100) at 300 °C. The α emission spectra of the refractory films are well-resolved, suggesting that they could be used as radioactive implants for brachytherapy and related treatments.

Reaction of Cyanide with Hg0-Contaminated Gold Mining Tailings Produces Soluble Mercuric Cyanide Complexes.

Elemental mercury (Hg0) contamination in artisanal and small-scale gold mining (ASGM) communities is widespread, and Hg0-contaminated tailings are often reprocessed with cyanide (-CN) to extract residual gold remaining after amalgamation. Hg0 reacts with -CN under aerobic conditions to produce Hg(CN)42- and other Hg(CN)nn-2 complexes. The production of solvated Hg(CN)nn-2 complexes increases upon agitation in the presence of synthetic and authentic Hg0-contaminated tailings that aid in dispersing the Hg0, increasing its reactive surface area. Adult rats were exposed to various concentrations of Hg(CN)2, and accumulation in organs and tissues was quantified using direct mercury analysis. The primary site of Hg(CN)2 accumulation was the kidney, although accumulation was also detected in the liver, spleen, and blood. Little accumulation was observed in the brain, suggesting that Hg(CN)2 complexes do not cross the blood-brain barrier. Renal tissue was particularly sensitive to the effects of Hg(CN)2, with pathological changes observed at low concentrations. Hg(CN)2 complexes are handled by mammalian systems in a manner similar to other inorganic species of Hg, yet appear to be more toxic to organ systems. The findings from this study are the first to show that Hg(CN)2 complexes are highly stable complexes that can lead to cellular injury and death in mammalian organ systems.

3D Printed Model of Extrahepatic Biliary Ducts for Biliary Stent Testing.

Several inflammatory conditions of the bile ducts cause strictures that prevent the drainage of bile into the gastrointestinal tract. Non-pharmacological treatments to re-establish bile flow include plastic or self-expanding metal stents (SEMs) that are inserted in the bile ducts during endoscopic retrograde cholangiopancreatography (ERCP) procedures. The focus of this study was to 3D print an anatomically accurate model of the extrahepatic bile ducts (EHBDs) with tissue-like mechanical properties to improve in vitro testing of stent prototypes. Following generation of an EHBD model via computer aided design (CAD), we tested the ability of Formlabs SLA 3D printers to precisely print the model with polymers selected based on the desired mechanical properties. We found the printers were reliable in printing the dimensionally accurate EHBD model with candidate polymers. Next, we evaluated the mechanical properties of Formlabs Elastic (FE), Flexible (FF), and Durable (FD) resins pre- and post-exposure to water, saline, or bile acid solution at 37 °C for up to one week. FE possessed the most bile duct-like mechanical properties based on its elastic moduli, percent elongations at break, and changes in mass under all liquid exposure conditions. EHBD models printed in FE sustained no functional damage during biliary stent deployment or when tube connectors were inserted, and provided a high level of visualization of deployed stents. These results demonstrate that our 3D printed EHBD model facilitates more realistic pre-clinical in vitro testing of biliary stent prototypes.

Quantifying the Interdependence of Metal-Ligand Covalency and Bond Distance Using Ligand K-edge XAS.

Bond distance is a common structural metric used to assess changes in metal-ligand bonds, but it is not clear how sensitive changes in bond distances are with respect to changes in metal-ligand covalency. Here we report ligand K-edge XAS studies on Ni and Pd complexes containing different phosphorus(III) ligands. Despite the large number of electronic and structural permutations, P K-edge pre-edge peak intensities reveal a remarkable correlation that spectroscopically quantifies the linear interdependence of covalent M-P σ bonding and bond distance. Cl K-edge studies conducted on many of the same Ni and Pd compounds revealed a poor correlation between M-Cl bond distance and covalency, but a strong correlation was established by analyzing Cl K-edge data for Ti complexes with a wider range of Ti-Cl bond distances. Together these results establish a quantitative framework to begin making more accurate assessments of metal-ligand covalency using bond distances from readily-available crystallographic data.

Crystal structure of (OC)5W(µ-dppe)W(CO)5.

The centrosymmetric title complex, [µ-ethane-1,2-diylbis(di-phenyl-phosphane)-κ2P:P']bis-[penta-carbonyl-tungsten(0)], [W2(C26H24P2)(CO)10], consists of two W(CO)5 moieties bridged by a bis-(di-phenyl-phosphan-yl)ethane (dppe) ligand. The W0 atom has a slightly distorted octa-hedral coordination environment consisting of 5 carbonyl ligands and one P atom from the bridging dppe ligand with the nearest W0 atom 5.625 (5) Šaway. The complex resides on a center of symmetry.

Impact of Coordination Geometry, Bite Angle, and Trans Influence on Metal-Ligand Covalency in Phenyl-Substituted Phosphine Complexes of Ni and Pd.

Despite the long-standing use of phosphine and diphosphine ligands in coordination chemistry and catalysis, questions remain as to their effects on metal-ligand bonding in transition metal complexes. Here we report ligand K-edge XAS, DFT, and TDDFT studies aimed at quantifying the impact of coordination geometry, diphosphine bite angle, and phosphine trans influence on covalency in M-P and M-Cl bonds. A series of four-coordinate NiCl2 and PdCl2 complexes containing PPh3 or Ph2P(CH2)nPPh2, where n = 1 (dppm), 2 (dppe), 3 (dppp), and 4 (dppb), was analyzed. The XAS data revealed that changing the coordination geometry from tetrahedral in Ni(PPh3)2Cl2 (1) to square planar in Ni(dppe)Cl2 (2) more than doubles the intensity of pre-edge features assigned to Ni-P and Ni-Cl 1s → σ* transitions. By way of comparison, varying the diphosphine in Pd(dppm)Cl2 (4), Pd(dppp)Cl2 (6), and Pd(dppb)Cl2 (7) yielded Pd-P 1s → σ* transitions with identical intensities, but a 10% increase was observed in the P K-edge XAS spectrum of Pd(dppe)Cl2 (5). A similar observation was made when comparing Ni(dppe)Cl2 (2) to Ni(dppp)Cl2 (3), and DFT and TDDFT calculations corroborated XAS results obtained for both series. Comparison of the spectroscopic and theoretical results to the diphosphine structures revealed that changes in M-P covalency were not correlated to changes in bite angles or coordination geometry. As a final measure, P and Cl K-edge XAS data were collected on trans-Pd(PPh3)2Cl2 (8) for comparison to the cis diphosphine complex Pd(dppe)Cl2 (5). Consistent with phosphine's stronger trans influence compared to chloride, a 35% decrease in the intensity of the Pd-P 1s → σ* pre-edge feature and a complementary 34% increase in Pd-Cl 1s → σ* feature was observed for 8 (trans) compared to 5 (cis). Overall, the results reveal how coordination geometry, ligand arrangement, and diphosphine structure affect covalent metal-phosphorus and metal-chloride bonding in these late transition metal complexes.

Reinvestigation of Np2Se5: a clear divergence from Th2S5 and Th2Se5 in chalcogen-chalcogen and metal-chalcogen interactions.

Single crystals of Np2Se5 have been prepared through the reactions of Np and Se at 1223 K in an Sb2Se3 flux. The structure of Np2Se5, which has been characterized by single-crystal X-ray diffraction methods, crystallizes in the tetragonal space group P42/nmc. The crystallographic unit cell includes one unique Np and two Se positions. Se(1) atoms form one-dimensional infinite chains along the a and b axes with alternating intermediate Se-Se distances of 2.6489 (8) and 2.7999 (8) Å, whereas Se(2) is a discrete Se(2-) anion. Each Np is coordinated to 10 Se atoms and every NpSe10 polyhedron shares faces, edges, or vertices with 14 other identical metal polyhedra to form a complex three-dimensional structure. Np LIII-edge X-ray Absorption Near Edge Structure (XANES) measurements show a clear shift in edge position to higher energies for Np2Se5 compared to Np3Se5 (Np(3+)2Np(4+)Se(2-)5). Magnetic susceptibility measurements indicate that Np2Se5 undergoes a ferromagnetic-type ordering below 18(1) K. Above the transition temperature, Np2Se5 behaves as a paramagnet with an effective moment of 1.98(5) µB/Np, given by a best fit of susceptibilities to a modified Curie-Weiss law over the temperature range 50-320 K.

Synthesis, properties, and complex crystal structure of Th2Se5.

The compound Th(2)Se(5) has been synthesized and its structure determined by means of single-crystal X-ray diffraction methods. The subcell of Th(2)Se(5) is in the tetragonal space group P4(2)/nmc and is isostructural to Np(2)Se(5). The modulated structure of Th(2)Se(5) has been solved in the monoclinic super space group P2(α0γ)0. The structure features parallel infinite Se-Se chains with minimum and maximum Se-Se distances of 2.477(5) and 2.967(5) Å, respectively. Th(2)Se(5) is a semiconductor with an electrical resistivity that shows thermally activated Arrhenius behavior with an activation energy of 0.40(1) eV. From spectroscopic measurements, the band gap of Th(2)Se(5) is 0.37(2) eV. That the Th(2)Se(5) structure is modulated whereas the Np(2)Se(5) structure appears not to be implies that the formal oxidation state of Np in Np(2)Se(5) is 4+.

Synthesis and structural diversity of barium (N,N-dimethylamino)diboranates.

The reaction of a slurry of BaBr(2) in a minimal amount of tetrahydrofuran (THF) with 2 equiv of Na(H(3)BNMe(2)BH(3)) in diethyl ether followed by crystallization from diethyl ether at -20 °C yields crystals of Ba(H(3)BNMe(2)BH(3))(2)(Et(2)O)(2) (1). Drying 1 at room temperature under vacuum gives the partially desolvated analogue Ba(H(3)BNMe(2)BH(3))(2)(Et(2)O)(x) (1') as a free-flowing white solid, where the value of x varies from <0.1 to about 0.4 depending on whether desolvation is carried out with or without heating. The reaction of 1 or 1' with Lewis bases that bind more strongly to barium than diethyl ether results in the formation of new complexes Ba(H(3)BNMe(2)BH(3))(2)(L), where L = 1,2-dimethoxyethane (2), N,N,N',N'-tetramethylethylenediamine (3), 12-crown-4 (4), 18-crown-6 (5), N,N,N',N'-tetraethylethylenediamine (6), and N,N,N',N",N"-pentamethylethylenetriamine (7). Recrystallization of 4 and 5 from THF affords the related compounds Ba(H(3)BNMe(2)BH(3))(2)(12-crown-4)(THF)·THF (4') and Ba(H(3)BNMe(2)BH(3))(2)(18-crown-6)·2THF (5'). In addition, the reaction of BaBr(2) with 2 equiv of Na(H(3)BNMe(2)BH(3)) in the presence of diglyme yields Ba(H(3)BNMe(2)BH(3))(2)(diglyme)(2) (8), and the reaction of 1 with 15-crown-5 affords the diadduct [Ba(15-crown-5)(2)][H(3)BNMe(2)BH(3)](2) (9). Finally, the reaction of BaBr(2) with Na(H(3)BNMe(2)BH(3)) in THF, followed by the addition of 12-crown-4, affords the unusual salt [Na(12-crown-4)(2)][Ba(H(3)BNMe(2)BH(3))(3)(THF)(2)] (10). All of these complexes have been characterized by IR and (1)H and (11)B NMR spectroscopy, and the structures of compounds 1-3, 4', 5', and 6-10 have been determined by single-crystal X-ray diffraction. As the steric demand of the Lewis bases increases, the structure changes from polymers to dimers to monomers and then to charge-separated species. Despite the fact that several of the barium complexes are monomeric in the solid state, none is appreciably volatile up to 200 °C at 10(-2) Torr.

Synthesis of the long-sought unsubstituted aminodiboranate Na(H3B-NH2-BH3) and its N-alkyl analogs.

Reduction of ammonia borane, NH(3) x BH(3), with Na or NaNH(2) in refluxing tetrahydrofuran (thf) affords the new compound, the unsubstituted aminodiboranate Na(BH(3)-NH(2)-BH(3)) (1a). Similar N-alkyl- and N,N-dialkylaminodiboranate salts, Na(H(3)B-NHMe-BH(3)) (1b), Na(H(3)B-NHEt-BH(3)) (1c), Na(H(3)B-NMeEt-BH(3)) (1d), Na[H(3)B-N(C(4)H(8))-BH(3)] (1e), and Na[H(3)B-N(C(5)H(10))-BH(3)] (1f), where N(C(4)H(8)) = pyrrolido and N(C(5)H(10)) = piperido, have also been prepared, along with their adducts with dioxane Na[H(3)B-NRR'-BH(3)](diox)(x) where x = 0.5 or 1.0 (2a-f). Crystal structures of 2b, 2c, and 2e are reported. Treatment of ErCl(3) with Na(H(3)B-NH(2)-BH(3)) in thf affords the new erbium complex Er(H(3)B-NH(2)-BH(3))Cl(2)(thf)(3), 3, which has been crystallographically characterized. (1)H and (11)B NMR spectra of the new compounds are reported.

Nanoenergetic materials: boron nanoparticles from the pyrolysis of decaborane and their functionalisation.

The surfaces of boron nanoparticles 10-150 nm in diameter, prepared by gas phase pyrolysis of decaborane vapour at 1 atm and 700-900 degrees C, can be halogenated by treatment with Br2 or XeF2; the surface halogenation somewhat increases the onset temperature for the oxidation of the particles under O2.