10-Valence-Electron C≡O and the 14-VE C≡Pt: Two Triple-Bonded Isoelectronic Families Differing by a dδ4 Ring.

10-VE A≡A' Diatomics, such as N≡N, C≡O, etc., have a strong σ2π4 triple bond plus a lone pair at each end. In our studies on 14-VE A≡B systems, such as C≡Pt, we find a similar bonding system plus a (5dδ)4 ring. Here, the A atom belongs to groups 13-17 and the B atom to groups 7-11. Also the BB' combinations, triatomics, such as PtCO or DsCO or uranyl, and longer chains, such as AuCN and [NC-Au-CN]-, are discussed. The δ ring directly contributes to nuclear quadrupole coupling constants, and DFT calculations using the BH and H or mPW1K functionals reproduce the experimental trends of the NQCC.

Determining nuclear quadrupole moments of Bi and Sb from molecular data.

An independent value of -422(3) millibarn (mb) is obtained for the nuclear quadrupole moment Q(209Bi) using experimental coupling constants for diatomic BiN, BiP, BiF, BiCl, and BiI, combined with full-Dirac CCSD-T calculations of the electric field gradient q. This value lies close to two other recently published molecular results, and a full-triplet CCSDT atomic result. Based on the same approach, we obtained Q(121Sb) = -541.7(0.8) mb and Q(123Sb) = -690.6( 1.0) mb, in agreement with one recently published molecular result.

Understanding the Uniqueness of 2p Elements in Periodic Tables.

The Periodic Table, and the unique chemical behavior of the first element in a column (group), were discovered simultaneously one and a half centuries ago. Half a century ago, this unique chemistry of the light homologs was correlated to the then available atomic orbital (AO) radii. The radially nodeless 1s, 2p, 3d, 4f valence AOs are particularly compact. The similarity of r(2s)≈r(2p) leads to pronounced sp-hybrid bonding of the light p-block elements, whereas the heavier p elements with n≥3 exhibit r(ns) ≪ r(np) of approximately -20 to -30 %. Herein, a comprehensive physical explanation is presented in terms of kinetic radial and angular, as well as potential nuclear-attraction and electron-screening effects. For hydrogen-like atoms and all inner shells of the heavy atoms, r(2s) ≫ r(2p) by +20 to +30 %, whereas r(3s)≳r(3p)≳r(3d), since in Coulomb potentials radial motion is more radial orbital expanding than angular motion. However, the screening of nuclear attraction by inner core shells is more efficient for s than for p valence shells. The uniqueness of the 2p AO is explained by this differential shielding. Thereby, the present work paves the way for future physical explanations of the 3d, 4f, and 5g cases.

The periodic table and the physics that drives it.

Mendeleev's introduction of the periodic table of elements is one of the most important milestones in the history of chemistry, as it brought order into the known chemical and physical behaviour of the elements. The periodic table can be seen as parallel to the Standard Model in particle physics, in which the elementary particles known today can be ordered according to their intrinsic properties. The underlying fundamental theory to describe the interactions between particles comes from quantum theory or, more specifically, from quantum field theory and its inherent symmetries. In the periodic table, the elements are placed into a certain period and group based on electronic configurations that originate from the Pauli and Aufbau principles for the electrons surrounding a positively charged nucleus. This order enables us to approximately predict the chemical and physical properties of elements. Apparent anomalies can arise from relativistic effects, partial-screening phenomena (of type lanthanide contraction) and the compact size of the first shell of every l-value. Further, ambiguities in electron configurations and the breakdown of assigning a dominant configuration, owing to configuration mixing and dense spectra for the heaviest elements in the periodic table. For the short-lived transactinides, the nuclear stability becomes an important factor in chemical studies. Nuclear stability, decay rates, spectra and reaction cross sections are also important for predicting the astrophysical origin of the elements, including the production of the heavy elements beyond iron in supernova explosions or neutron-star mergers. In this Perspective, we critically analyse the periodic table of elements and the current status of theoretical predictions and origins for the heaviest elements, which combine both quantum chemistry and physics.

Simple Estimates for Eutectic Behavior.

A simple formula is derived for the eutectic point of an A-B system in terms of the monomer melting points and melting enthalpies. This estimate is tested on several non-ionic or ionic systems, with or without common ions, including choline chloride/urea mixtures. The results are compared with the Schröder-van Laar equation.

Chemistry of the 5g Elements: Relativistic Calculations on Hexafluorides.

A Periodic System was proposed for the elements 1-172 by Pyykkö on the basis of atomic and ionic calculations. In it, the elements 121-138 were nominally assigned to a 5g row. We now perform molecular, relativistic four-component DFT calculations and find that the hexafluorides of the elements 125-129 indeed enjoy occupied 5g states.

Is the chemistry of lawrencium peculiar?

It is explicitly verified that the atomic 7p(1) ground-state configuration of Lr originates from relativistic effects. Without relativity one has 6d(1). All three ionization potentials IP1-3 of Lr resemble those of Lu. Simple model studies on mono- and trihydrides, monocarbonyls or trichlorides suggest no major chemical differences between Lr and the lanthanides.

Is Octavalent Pu(VIII) Possible? Mapping the Plutonium Oxyfluoride Series PuO(n)F(8-2n) (n = 0-4).

While the oxidation state Pu(VIII) is shown to be less stable than Pu(V) in the PuO4 molecule, it is not clear if the more electronegative fluorine can help to stabilize Pu(VIII). Our calculations on PuO(n)F(8-2n) (n = 0-4) molecules notably confirm that PuO2F4 has both (1)D(4h) and (5)C(2v) minima with the oxidation states Pu(VIII) and Pu(V), respectively, with the latter having lower energy. The hybrid-DFT, CCSD(T), and CASSCF methods all give the same result. The results conform to a superoxide ligand when n ≥ 2. PuF8 in a (1)O(h) state can decompose to PuF6 and F2, and PuOF6 in a (1)C(2v) state also can break down to PuF6 and 1/2 O2. The Pu(VIII) anion PuO2F5(-) does have a D(5h) minimum, which also lies above a (5)C(2v) Pu(V) peroxide structure. However, the energy differences between the different minima are not large, indicating that metastable species with oxidation states higher than Pu(V) cannot be completely excluded.

On the Extreme Oxidation States of Iridium.

It has recently been suggested that the oxidation states of Ir run from the putative -III in the synthesized solid Na3 [Ir(CO)3 ] to the well-documented +IX in the species IrO4 (+) . Furthermore, [Ir(CO)3 ](3-) was identified as an 18-electron species. A closer DFT study now finds support for this picture: The orbitals spanned by the 6s,6p,5d orbitals of the iridium are all occupied. Although some have considerable ligand character, the deviations from 18 e leave the orbital symmetries unchanged. The isoelectronic systems from Os(-IV) to Au(-I) behave similarly, suggesting further possible species. To paraphrase Richard P. Feynmann "there is plenty of room at the bottom".

Additive covalent radii for single-, double-, and triple-bonded molecules and tetrahedrally bonded crystals: a summary.

The recent fits of additive covalent radii R(AB) = r(A) + r(B) for the title systems are reviewed and compared with alternative systems of radii by other authors or with further experimental data. The agreement of the predicted R with experiment is good, provided that the A-B bond is not too ionic, or the coordination numbers of the two atoms too different from the original input data, used in the fit. Bonds between transition metals and halides are not included in the single-bond set, because of their partial multiple-bond character.

Structural and photophysical study on heterobimetallic complexes with d8-d10 interactions supported by carborane ligands: theoretical analysis of the emissive behaviour.

Heterobimetallic complexes of formula [M{(PPh2)2C2B9H10}(S2C2B10 H10)M'(PPh3)] (M=Pd, Pt; M'=Au, Ag, Cu) and [Ni{(PPh2)2C2B9H10}(S2C2B10H10)Au(PPh3)] were obtained from the reaction of [M{(PPh2)2C2B10H10}(S2C2B10H10)] (M=Pd, Pt) with [M'(PPh3)](+) (M'=Au, Ag, Cu) or by one-pot synthesis from [(SH2C2B10H10], (PPh2 )2C2B10H10, NiCl2 ⋅6 H2 O, and [Au(PPh3)](+). They display d(8)-d(10) intermetallic interactions and emit red light in the solid state at 77 K. Theoretical studies on [M{(PPh2)2C2B9H10}(S2C2B10H10)Au(PPh3)] (M=Pd, Pt, Ni) attribute the luminescence to ligand (thiolate, L)-to-"P2-M-S2" (ML') charge-transfer (LML'CT) transitions for M=Pt and to metal (M)-to-"P2-M-S2" (ML') charge-transfer (MML'CT) transitions for M=Ni, Pd.

The RTAM electronic bibliography, version 17.0, on relativistic theory of atoms and molecules.

The RTAM bibliography is freely available at rtam.csc.fi and the Version 17.0 of August 22, 2013 now contains 16,566 items from the year 1916-2013. "Production works" were systematically covered until 1999. Since the year 2000, mainly methodological papers were included. The methods and principles behind RTAM are described.

Unbridged Au(II)-Au(II) bonds are theoretically allowed.

The bonding in the unbridged closed-shell Au(II)-Au(II) dimers X(4)Au(2)(C(5)H(5)N)(2), X = H, F-I and CF(3), is analyzed and the short Au-Au bonds around 250 pm are reproduced by a novel 6s6p(z)5d(xy) hybridization.

Relativistic effects in chemistry: more common than you thought.

Relativistic effects can strongly influence the chemical and physical properties of heavy elements and their compounds. This influence has been noted in inorganic chemistry textbooks for a couple of decades. This review provides both traditional and new examples of these effects, including the special properties of gold, lead-acid and mercury batteries, the shapes of gold and thallium clusters, heavy-atom shifts in NMR, topological insulators, and certain specific heats.

Predicting new, simple inorganic species by quantum chemical calculations: some successes.

A combination of ab initio calculations with the isoelectronic principle and chemical intuition is a useful way to predict new species. Some experimentally verified examples are (1) the transition-metal hydrides, MH(n) (n = 4-12), (2) new members of the multiply-bonded 2nd- or 3rd-period species A≡B, A=B=C, A=B=C=D or A≡B-C≡D, and A=B=C=D=E classes, the last-mentioned class including the cations N and OCNCO(+), (3) new members of the uranyl isoelectronic series, (4) actinyls where one of the oxygens is replaced by a 5d transition-metal (TM), (5) certain systems with noble-gas-noble-metal bonds, (6) the first argon compound HArF, (7) the cluster series of WAu(12), (8) TM-centred polyazide anions, (9) covalent molecules with a central -Zn-Zn- bond, (10) tetrahedral clusters of zinc and cadmium, (11) model systems for otherwise missing multiple bonds and (12) certain endohedral A@B systems. Further series of hypothetical species were used as a tool for developing recent sets of covalent radii, for studying the endohedral intermolecular interactions in A@B systems, or for finding examples of a 32-electron rule, corresponding to the well-known 8e- and 18e-rules. For obvious reasons, much of the molecular chemistry of the superheavy elements is based on studies of hypothetical model systems.

Molecular hydrogen tweezers: structure and mechanisms by neutron diffraction, NMR, and deuterium labeling studies in solid and solution.

The mechanism of reversible hydrogen activation by ansa-aminoboranes, 1-N-TMPH-CH(2)-2-[HB(C(6)F(5))(2)]C(6)H(4) (NHHB), was studied by neutron diffraction and thermogravimetric mass-spectroscopic experiments in the solid state as well as with NMR and FT-IR spectroscopy in solution. The structure of the ansa-ammonium borate NHHB was determined by neutron scattering, revealing a short N-H···H-B dihydrogen bond of 1.67 Å. Moreover, this intramolecular H-H distance was determined in solution to be also 1.6-1.8 Å by (1)H NMR spectroscopic T(1) relaxation and 1D NOE measurements. The X-ray B-H and N-H distances deviated from the neutron and the calculated values. The dynamic nature of the molecular tweezers in solution was additionally studied by multinuclear and variable-temperature NMR spectroscopy. We synthesized stable, individual isotopic isomers NDDB, NHDB, and NDHB. NMR measurements revealed a primary isotope effect in the chemical shift difference (p)Δ(1)H(D) = δ(NH) - δ(ND) (0.56 ppm), and hence supported dihydrogen bonding. The NMR studies gave strong evidence that the structure of NHHB in solution is similar to that in the solid state. This is corroborated by IR studies providing clear evidence for the dynamic nature of the intramolecular dihydrogen bonding at room temperature. Interestingly, no kinetic isotope effect was detected for the activation of deuterium hydride by the ansa-aminoborane NB. Theoretical calculations attribute this to an "early transition state". Moreover, 2D NOESY NMR measurements support fast intermolecular proton exchange in aprotic CD(2)Cl(2) and C(6)D(6).