Hexacoordinated nitrogen(V) stabilized by high pressure.

In all of its known connections nitrogen retains a valence shell electron count of eight therefore satisfying the golden rule of chemistry - the octet rule. Despite the diversity of nitrogen chemistry (with oxidation states ranging from + 5 to -3), and despite numerous efforts, compounds containing nitrogen with a higher electron count (hypervalent nitrogen) remain elusive and are yet to be synthesized. One possible route leading to nitrogen's hypervalency is the formation of a chemical moiety containing pentavalent nitrogen atoms coordinated by more than four substituents.

Krypton oxides under pressure.

Under high pressure, krypton, one of the most inert elements is predicted to become sufficiently reactive to form a new class of krypton compounds; krypton oxides. Using modern ab-initio evolutionary algorithms in combination with Density Functional Theory, we predict the existence of several thermodynamically stable Kr/O species at elevated pressures. In particular, our calculations indicate that at approx.

High-pressure stabilization of argon fluorides.

On account of the rapid development of noble gas chemistry in the past half-century both xenon and krypton compounds can now be isolated in macroscopic quantities. The same does not hold true for the next lighter group 18 element, argon, which forms only isolated molecules stable solely in low temperature matrices or supersonic jet streams. Here we present theoretical investigations into a new high-pressure reaction pathway, which enables synthesis of argon fluorides in bulk and at room temperature.

Ammonia as a case study for the spontaneous ionization of a simple hydrogen-bonded compound.

Modern ab initio calculations predict ionic and superionic states in highly compressed water and ammonia. The prediction apparently contradicts state-of-the-art experimentally established phase diagrams overwhelmingly dominated by molecular phases. Here we present experimental evidence that the threshold pressure of ~120 GPa induces in molecular ammonia the process of autoionization to yet experimentally unknown ionic compound--ammonium amide.

High-pressure formation and stabilization of binary iridium hydrides.

A new class of binary iridium hydrides (IrxHy) is investigated in the 1 atm to 125 GPa pressure range at the ab initio level, using DFT. Upon compression a number of hydrides are predicted to stabilize in the excess hydrogen environment. Static stabilization pressure is calculated to be ∼14 and ∼5 GPa at which a dihydride (Ibam, Z = 2) and a trihydride (P63mc, Z = 2) stabilize thermodynamically, respectively.

WH(n) under pressure.

An initial observation of the formation of WH under pressure from W gaskets surrounding hydrogen in diamond anvil cells led to a theoretical study of tungsten hydride phases. At P = 1 atm no stoichiometry is found to be stable with respect to separation into the elements, but as the pressure is raised WH(n) (n = 1-6, 8) stoichiometries are metastable or stable. WH and WH(4) are calculated to be stable at P > 15 GPa, WH(2) becomes stable at P > 100 GPa and WH(6) at P > 150 GPa.

High pressure stabilization and emergent forms of PbH4.

A wide decomposition pressure range of 132 GPa is predicted for PbH4 above which it emerges in very different forms compared with its group-14 congeners. This triply Born-Oppenheimer system is a nonmolecular, three-dimensional, metallic alloy, despite a prominent layered structure. A significant number of enthalpically near-degenerate structures, with exceedingly small energy barriers for distortions, and characteristic instabilities in the phonon spectra suggest that even at very high pressures PbH4 may exhibit both metallic and liquidlike properties and sublattice or even full melting.

Relativity and the mercury battery.

Comparative, fully relativistic (FR), scalar relativistic (SR) and non-relativistic (NR) DFT calculations attribute about 30% of the mercury-battery voltage to relativity. The obtained percentage is smaller than for the lead-acid battery, but not negligible.

Freezing in resonance structures for better packing: XeF2 becomes (XeF+)(F-) at large compression.

Recent high-pressure experiments conducted on xenon difluoride (XeF(2)) suggested that this compound undergoes several phase transitions up to 100 GPa, becoming metallic above 70 GPa. In this theoretical study, in contrast to experiment, we find that the ambient pressure molecular structure of xenon difluoride, of I4/mmm symmetry, remains the most stable one up to 105 GPa. In our computations, the structures suggested from experiment have either much higher enthalpies than the I4/mmm structure or converge to that structure upon geometry optimization.

Relativity and the lead-acid battery.

The energies of the solid reactants in the lead-acid battery are calculated ab initio using two different basis sets at nonrelativistic, scalar-relativistic, and fully relativistic levels, and using several exchange-correlation potentials. The average calculated standard voltage is 2.13 V, compared with the experimental value of 2.

Au(n)Hg(m) clusters: mercury aurides, gold amalgams, or van der Waals aggregates?

The class of bimetallic clusters, Au(n)M(m) (M = Zn, Cd, Hg), is calculated at the ab initio level using the DFT, RI-MP2, and CCSD(T) methods. For the triatomic Au2M (M = Zn, Cd), the auride-type linear Au-M-Au structures are preferred; for Au2Hg, the linear Au-Au-Hg "amalgam" is preferred. The mixed cation [HgAuHg]+, an analog of the known solid-state species Hg32+, is predicted.

Structure and bonding of the MCN molecules, M=Cu,Ag,Au,Rg.

High-precision calculations are reported for the title series with M=Cu, Ag, Au, using CCSD(T) with the latest pseudopotentials and basis sets up to cc-pVQZ. The bond lengths for M=Cu, Ag, Au agree with experiment within better than 1 pm. The role of deep-core excitations is studied.

Basis-set limit of the aurophilic attraction using the MP2 method: the examples of [ClAuPH3]2 dimer and [P(AuPH3)4]+ ion.

The basis-set limit of the aurophilic attraction is studied at the MP2 level for the free model dimer [ClAuPH(3)](2) and for a [P(AuPH(3))(4)](+) ion. The latter system is found to prefer a C(4v) symmetry, instead of T(d), in agreement with Li and Pyykko [Inorg. Chem.

From nanostrips to nanorings: the elastic properties of gold-glued polyauronaphthyridines and polyacenes.

The previously proposed flat 2,6-diauro-1,5-naphthyridine polymers were bent to closed rings with up to 12 monomers. Their bending energies and lowest in-plane deformation frequencies were calculated at the DFT level using quasirelativistic pseudopotentials for gold. The ring-formation energies were compared with those for polyacene rings and found to be of the same order of magnitude, suggesting sufficient stability for the predicted polyauronaphthyridines.

Gold as intermolecular glue: a theoretical study of nanostrips based on quinoline-type monomers.

A family of infinite nanostrips is computationally predicted. In it monomers of single, double or triple aromatic rings are linked to each other by strong C-Au-C, C-Au <-- N or N --> Au <-- N bonds. Depending on the geometry of the system and saturation of the bonds, these 1-D nanostrips are found to be insulators, narrow- or zero-gap semiconductors, or metals.