Laser-Ablated U Atom Reactions with (CN)2 to Form UNC, U(NC)2, and U(NC)4: Matrix Infrared Spectra and Quantum Chemical Calculations.

Laser-ablated U atoms react with (CN)2 in excess argon and neon during codeposition at 4 K to form UNC, U(NC)2, and U(NC)4 as the major uranium-bearing products, which are identified from their matrix infrared spectra using cyanogen substituted with 13C and 15N and from quantum chemical calculations. The 12/13CN and C14/15N isotopic frequency ratios computed for the U(NC)1,2,4 molecules agree better with the observed values than those calculated for the U(CN)1,2,4 isomers. Multiplets using mixed isotopic cyanogens reveal the stoichiometries of these products, and the band positions and quantum chemical calculations confirm the isocyanide bonding arrangements, which are 14 and 51 kJ/mol more stable than the cyanide isomers for UNC and U(NC)2, respectively, and 62 kJ/mol for U(NC)4 in the isolated gas phase at the CCSD(T)/CBS level. The studies further demonstrate that the isocyano nitrogen is a better π donor, so it interacts with U(VI) better than carbon. Although the higher isocyanides are more stable than the corresponding cyanides, U(NC)5 and U(NC)6 were not observed here most likely because unfavorable or endothermic routes are required for their production from U(NC)4. The computed U-NC bond dissociation energies decrease from 581 kJ/mol for 4[UNC] to 168 kJ/mol for 1[U(NC)6 ]. The ionic nature of U(NC)n decreases as the number of isocyano groups increases.

Structural and Theoretical Study of Salts of the [B9 H14 ]- Ion: Isolation of Multiple Isomers and Implications for Energy Storage.

Invited for this month's cover are the research groups of Prof. Robin Rogers, based at McGill University, and Prof. David Dixon, based at The University of Alabama. The cover picture shows two isomers of [B9 H14 ]- which coexist in a crystalline salt, the mirror symmetric form on the left and the unsymmetrical form on the right. Read the full text of the article at 10.1002/cplu.201600270.

Structural and Theoretical Study of Salts of the [B9 H14 ]- Ion: Isolation of Multiple Isomers and Implications for Energy Storage.

Boranes and boron hydrides are well known for their novel molecular structures and useful chemical reactivity, with [B9 H14 ]- notable in particular for its ease of isolation, unusual structure, and tautomerization. We report an experimental and theoretical investigation of the structure of [B9 H14 ]- and the energetics of some of its reactions. Salts of [B9 H14 ]- with 1-ethyl-3-methylimidazolium and N-butyl-N-methylpyrrolidinium were characterized by single-crystal X-ray diffraction and demonstrate the stabilization of an isomer of [B9 H14 ]- not previously observed in the solid state. Heats of formation and acid dissociation constants of [B9 H14 ]- and closely related structures were calculated. The results suggest a mechanism for particularly energetic hypergolic ignition induced by protonation and suggest potential for reversible H2 storage. These results encourage further investigation of [B9 H14 ]- as an energy-storage medium in ionic systems.

Reactions of laser-ablated U atoms with (CN)2: infrared spectra and electronic structure calculations of UNC, U(NC)2, and U(NC)4 in solid argon.

Reactions of laser-ablated U atoms with (CN)2 produce UNC, U(NC)2, and U(NC)4 as the major products, identified from their Ar matrix infrared spectra and precursors partially and fully substituted with (13)C and (15)N. Mixed isotopic multiplets substantiate product stoichiometries. Band positions and quantum chemical calculations verify the isocyanide bonding.

Bis-BN cyclohexane: a remarkably kinetically stable chemical hydrogen storage material.

A critical component for the successful development of fuel cell applications is hydrogen storage. For back-up power applications, where long storage periods under extreme temperatures are expected, the thermal stability of the storage material is particularly important. Here, we describe the development of an unusually kinetically stable chemical hydrogen storage material with a H2 storage capacity of 4.7 wt%. The compound, which is the first reported parental BN isostere of cyclohexane featuring two BN units, is thermally stable up to 150 °C both in solution and as a neat material. Yet, it can be activated to rapidly desorb H2 at room temperature in the presence of a catalyst without releasing other detectable volatile contaminants. We also disclose the isolation and characterization of two cage compounds with S4 symmetry from the H2 desorption reactions.

Unusual structure, bonding and properties in a californium borate.

The participation of the valence orbitals of actinides in bonding has been debated for decades. Recent experimental and computational investigations demonstrated the involvement of 6p, 6d and/or 5f orbitals in bonding. However, structural and spectroscopic data, as well as theory, indicate a decrease in covalency across the actinide series, and the evidence points to highly ionic, lanthanide-like bonding for late actinides. Here we show that chemical differentiation between californium and lanthanides can be achieved by using ligands that are both highly polarizable and substantially rearrange on complexation. A ligand that suits both of these desired properties is polyborate. We demonstrate that the 5f, 6d and 7p orbitals are all involved in bonding in a Cf(III) borate, and that large crystal-field effects are present. Synthetic, structural and spectroscopic data are complemented by quantum mechanical calculations to support these observations.

Electronic structure predictions of the properties of non-innocent P-ligands in group 6B transition metal complexes.

Neutral group 6B (Cr, Mo, W) pentacarbonyl complexes M(CO)5-L possessing various P-ligands such as phosphines, phosphaalkenes, and phospha-quinomethanes can form radical cations and anions under redox conditions. There is significant interest in whether the radical site is localized on the metal or on a "non-innocent" ligand. Density functional theory was used to predict whether the radicals of the complexes behave as metal or ligand-centered radicals and whether these compounds could form in solution or as an ion pair with various oxidizing and reducing agents. The quinone-like ligands are predicted to be ligand centered radicals when they are anions and metal centered radicals when they are cations. The predicted reaction energies for single electron transfer (SET) reactions involving the quinone like ligands are negative or near thermoneutral for both radicals in polar solutions and as solid state ion pairs. The energetics of the SET reactions can be controlled by the nature of L, the nature of the oxidizing/reducing agent, and the solvent polarity. Such complexes could be used as flexible catalysts for single electron transfer reactions.

Lewis base assisted B-H bond redistribution in borazine and polyborazylene.

Lewis bases react with borazine and polyborazylene, yielding borane adducts. In the case of NH3 (l), ammonia-borane (AB) is formed and quantified using NMR spectroscopy against an internal standard. Calculations indicate that the formation of B(NH2)3 may provide the driving force of this redistribution. Given the complexity and expense of currently known spent AB regeneration pathways, it is suggested that this redistribution chemistry be used to recover AB and improve regeneration methods.

3-Methyl-1,2-BN-cyclopentane: a promising H2 storage material?

We provide detailed characterization of properties for 3-methyl-1,2-BN-cyclopentane 1 that are relevant to H(2) storage applications such as viscosity, thermal stability, H(2) gas stream purity, and polarity. The viscosity of 1 at room temperature is 25 ± 5 cP, about one fourth the viscosity of olive oil. TGA/MS analysis indicates that liquid carrier 1 is thermally stable at 30 °C but decomposes slowly at 50 °C. RGA data suggest that the H(2) desorption from 1 is a clean process, producing relatively pure H(2) gas. Compound 1 is a polar zwitterionic-type liquid consistent with theoretical predictions and solvatochromic studies.

Binary group 15 polyazides. structural characterization of [Bi(N3)4]-, [Bi(N3)5]2-, [bipy·Bi(N3)5]2-, [Bi(N3)6]3-, bipy·As(N3)3, bipy·Sb(N3)3, and [(bipy)2·Bi(N3)3]2 and on the lone pair activation of valence electrons.

The binary group 15 polyazides As(N(3))(3), Sb(N(3))(3), and Bi(N(3))(3) were stabilized by either anion or donor-acceptor adduct formation. Crystal structures are reported for [Bi(N(3))(4)](-), [Bi(N(3))(5)](2-), [bipy·Bi(N(3))(5)](2-), [Bi(N(3))(6)](3-), bipy·As(N(3))(3), bipy·Sb(N(3))(3), and [(bipy)(2)·Bi(N(3))(3)](2). The lone valence electron pair on the central atom of these pnictogen(+III) compounds can be either sterically active or inactive. The [Bi(N(3))(5)](2-) anion possesses a sterically active lone pair and a monomeric pseudo-octahedral structure with a coordination number of 6, whereas its 2,2'-bipyridine adduct exhibits a pseudo-monocapped trigonal prismatic structure with CN 7 and a sterically inactive lone pair. Because of the high oxidizing power of Bi(+V), reactions aimed at Bi(N(3))(5) and [Bi(N(3))(6)](-) resulted in the reduction to bismuth(+III) compounds by [N(3)](-). The powder X-ray diffraction pattern of Bi(N(3))(3) was recorded at 298 K and is distinct from that calculated for Sb(N(3))(3) from its single-crystal data at 223 K. The [(bipy)(2)·Bi(N(3))(3)](2) adduct is dimeric and derived from two BiN(8) square antiprisms sharing an edge consisting of two µ(1,1)-bridging N(3) ligands and with bismuth having CN 8 and a sterically inactive lone pair. The novel bipy·As(N(3))(3) and bipy·Sb(N(3))(3) adducts are monomeric and isostructural and contain a sterically active lone pair on their central atom and a CN of 6. A systematic quantum chemical analysis of the structures of these polyazides suggests that the M06-2X density functional is well suited for the prediction of the steric activity of lone pairs in main-group chemistry. Furthermore, it was found that the solid-state structures can strongly differ from those of the free gas-phase species or those in solutions and that lone pairs that are sterically inactive in a chemical surrounding can become activated in the free isolated species.

Nucleophilic aromatic substitution reactions of 1,2-dihydro-1,2-azaborine.

Could go either way: the addition of nucleophiles to the parent 1,2-dihydro-1,2-azaborine and subsequent quenching with an electrophile generates novel substituted 1,2-azaborine derivatives. Mechanistic studies are consistent with two distinct nucleophilic aromatic substitution pathways depending on the nature of the nucleophile.

Regeneration of ammonia borane spent fuel by direct reaction with hydrazine and liquid ammonia.

Ammonia borane (H(3)N-BH(3), AB) is a lightweight material containing a high density of hydrogen (H(2)) that can be readily liberated for use in fuel cell-powered applications. However, in the absence of a straightforward, efficient method for regenerating AB from dehydrogenated polymeric spent fuel, its full potential as a viable H(2) storage material will not be realized. We demonstrate that the spent fuel type derived from the removal of greater than two equivalents of H(2) per molecule of AB (i.e., polyborazylene, PB) can be converted back to AB nearly quantitatively by 24-hour treatment with hydrazine (N(2)H(4)) in liquid ammonia (NH(3)) at 40°C in a sealed pressure vessel.

Why are [P(C6H5)4](+)N3- and [As(C6H5)4](+)N3- ionic salts and Sb(C6H5)4N3 and Bi(C6H5)4N3 covalent solids? A theoretical study provides an unexpected answer.

A recent crystallographic study has shown that, in the solid state, P(C(6)H(5))(4)N(3) and As(C(6)H(5))(4)N(3) have ionic [M(C(6)H(5))(4)](+)N(3)(-)-type structures, whereas Sb(C(6)H(5))(4)N(3) exists as a pentacoordinated covalent solid. Using the results from density functional theory, lattice energy (VBT) calculations, sublimation energy estimates, and Born-Fajans-Haber cycles, it is shown that the maximum coordination numbers of the central atom M, the lattice energies of the ionic solids, and the sublimation energies of the covalent solids have no or little influence on the nature of the solids. Unexpectedly, the main factor determining whether the covalent or ionic structures are energetically favored is the first ionization potential of [M(C(6)H(5))(4)]. The calculations show that at ambient temperature the ionic structure is favored for P(C(6)H(5))(4)N(3) and the covalent structures are favored for Sb(C(6)H(5))(4)N(3) and Bi(C(6)H(5))(4)N(3), while As(C(6)H(5))(4)N(3) presents a borderline case.

Thermodynamic properties of the XO(2), X(2)O, XYO, X(2)O(2), and XYO(2) (X, Y = Cl, Br, and I) isomers.

High level ab initio electronic structure calculations at the coupled cluster level with a correction for triples extrapolated to the complete basis set limit have been made for the thermodynamics of the BrBrO(2), IIO(2), ClBrO(2), ClIO(2), and BrIO(2) isomers, as well as various molecules involved in the bond dissociation processes. Of the BrBrO(2) isomers, BrOOBr is predicted to be the most stable by 8.5 and 9.3 kcal/mol compared to BrBrO(2) and BrOBrO at 298 K, respectively. The weakest bond in BrOOBr is the O-Br bond with a bond dissociation energy (BDE) of 15.9 kcal/mol, and in BrBrO(2), it is the Br-Br bond of 19.1 kcal/mol. The smallest BDE in BrOBrO is for the central O-Br bond with a BDE of 12.6 kcal/mol. Of the IIO(2) isomers, IIO(2) is predicted to be the most stable by 3.3, 9.4, and 28.9 kcal/mol compared to IOIO, IOOI, and OIIO at 298 K, respectively. The weakest bond in IIO(2) is the I-I bond with a BDE of 22.2 kcal/mol. The smallest BDEs in IOIO and IOOI are the terminal O-I bonds with values of 19.0 and 5.2 kcal/mol, respectively.