Investigations in the ternary praseodymium–boron–carbon system: Solid-state phase diagram and structural chemistry

International audienceThe solid-state phase equilibrium in the Pr–B–C system was established using X-ray diffraction, scanning electron microscopy and electron probe microanalysis. The region up to 60 at % of Pr was studied at 1270 K, whereas the Pr-rich corner, due to the generally lower melting points, was investigated at 1070 K. Eleven ternary compounds were isolated. The existence of PrB2C2, Pr5B2C5, Pr5B4C5, Pr5B2C6, PrBC, and Pr10B9C12 was confirmed. Pr15B6C20 and Pr25B14C26 have been found only in arc-melted alloys. Three new ternary compounds were isolated, namely Pr2BC, ∼Pr4B3C13 and ∼Pr7B9C34. The monoclinic structure of Pr2BC was solved from X-ray single crystal data: space group C2/m (a = 13.088(1) Å, b = 3.6748(8) Å, c = 9.488(1) Å, β = 131.03(1)°, R1 = 0.035 (wR2 = 0.086) for 585 reflections with Io > 2σ (Io)). Additionally, the phase of Pr5B2C6 was analyzed showing a broad homogeneity range described by the formula Pr5(BC)x (7.5 ≤ x ≤ 9.3

Cross-cluster transition-metal bonding in oblato-nido dimetallaboranes unveiled by topological analysis

International audienceThe bonding situation for the oblato-nido dimetallaboranes (CpV)2B5H11 and ( Cp ∗ T ) 2 B 5 H 5 + x , where T = Ta, Cr, Mo, W, Re and Cp∗=C5Me5, was analyzed using the corresponding model series with Cp∗ replaced by the cyclopentadienyl C5Me5. The application of different bonding indicators revealed that both through-space and through-bond (via boron atoms of the ring) interactions account for a substantial metal-metal bon

Addition and elimination reactions of \H2\ in ruthenaborane clusters: A computational study

International audienceRuthenaborane clusters have been modelled by performing density functional theory calculations using the \B3LYP\ functional. The calculations gain insights into hydrogen storage and the H-H bond activation by ruthenaboranes. To study the nature of the chemical bond of \H2\ molecules attached to ruthenaboranes, we carried out structural optimizations for different ruthenaborane clusters and determined transition state structures for their hydrogenation addition/elimination reactions. Calculations of the reaction pathways yielded different transition-state structures involving molecular hydrogen bonded to the cluster or formation of metal hydrides. The H-H bond of \H2\ seems to be activated by the ruthenaborane clusters as activation energies of 24-42 kcal/mol were calculated for the \H2\ addition reaction. The calculated Gibbs free energy for the \H2\ addition reaction is 14-27 kcal/mol. The calculated activation energies and the molecular structures of the [(C5Me5)Ru2B10H16], [(C5Me5)Ru2B8H14] and [(C5Me5)Ru2B8H12] clusters with different degree of hydrogenation are compared. The mechanisms of the \H2\ addition and elimination reactions of the studied clusters suggest that they might be useful as hydrogen storage materials due to their ability to activate the H-H bond. They also serve as an example of the ability of hypoelectronic metallaboranes to reversibly or irreversibly bind hydrogen

Structural, electronic and magnetic properties of some early vs late transition dimetallaborane clusters - A theoretical investigation

International audienceThe strength of DFT methods in analyzing the electronic and magnetic properties of a series of dimetallaboranes of varied stoichiometry and architectural core, namely M2B3, M2B4 and M2B5 with both early- and late-transition metals is demonstrated. In particular, the observed 1H and 11B chemical shifts of most of the studied compounds are reproduced with a good accuracy of a few ppm at the DFT-GIAO BP86/TZ2P/SC level for the compounds with first-row transition metal elements and at the B3LYP/TZ2P/SO level for those with second- and third-row transition metal elements. This allows structural applications in elucidating the number and the location of bridging hydrogen atoms in experimentally poorly characterized metallaboranes such as (Cp*Cr)2B4H

Eu- and Tb-adsorbed Si3_{3}N4_{4} and Ge3_{3}N4_{4}: tuning the colours with one luminescent host

Phosphor-converted white light emitting diodes (pc-LEDs) are efficient light sources for applications in lighting and electronic devices. Nitrides, with their wide-ranging applicability due to their intriguing structural diversity, and their auspicious chemical and physical properties, represent an essential component in industrial and materials applications. Here, we present the successful adsorption of Eu and Tb at the grain boundaries of bulk β-Si$_{3}$N$_{4}$ and β-Ge$_{3}$N$_{4}$ by a successful combustion synthesis. The adsorption of europium and terbium, and the synergic combination of both, resulted in intriguing luminescence properties of all compounds (red, green, orange and yellow). In particular, the fact that one host can deliver different colours renders Eu,Tb-β-M$_{3}$N$_{4}$ (M = Si, Ge) a prospective chief component for future light emitting diodes (LEDs). For the elucidation of the electronic properties and structure of β-Si$_{3}$N$_{4}$ and β-Ge$_{3}$N$_{4}$, Mott–Schottky (MS) measurements and density functional theory (DFT) computations were conducted for the bare and RE adsorbed samples

Octahedral niobium cluster-based solid state halides and oxyhalides: effects of the cluster condensation via an oxygen ligand on electronic and magnetic properties

International audienceThe influences of an oxygen ligand on the structural, magnetic and electronic properties of octahedral niobium cluster-based oxides and oxychlorides are reported. The Nb6 metal cluster is edge-bridged by twelve inner ligands and additionally bonded to six apical ligands to form Nb6Li12La6 units (L = Cl, O) wherein oxygen and chlorine are perfectly ordered. Oxygen favours the interconnection of clusters via double Oi-a/Oa-i bridges in a similar way to the double Si-a/Sa-i bridges found in Chevrel phases based on face capped Mo6Li8La6 units. Periodic density functional theory (DFT) calculations confirm that increasing the number of inner oxygen ligands at the expense of chlorine atoms favours the 14 metal-electron (ME) count per octahedral cluster unit. It is also shown that weak interactions occur between neighbouring clusters. Indeed, magnetic measurements performed on AxNb6Cl12O2 (A = Rb, x = 0.816(8); A = Cs, x = 1) series containing 15-ME species evidence antiferromagnetic interactions at low temperatures. Broken-symmetry DFT calculations of exchange parameters within spin dimer analysis confirm the experimental results

SnCN₂: A Carbodiimide with an Innovative Approach for Energy Storage Systems and Phosphors in Modern LED Technology

The carbodiimide SnCN$_{2}$ was prepared at low temperatures (400 °C–550 °C) by using a patented urea precursor route. The crystal structure of SnCN$_{2}$ was determined from single‐crystal data in space group C2/c (no. 15) with a=9.1547(5), b=5.0209(3), c=6.0903(3) Å, β=117.672(3), V=247.92 Å$^{3}$ and Z=4. As carbodiimide compounds display remarkably high thermal and chemical resistivity, SnCN$_{2}$ has been doped with Eu and Tb to test it for its application in future phosphor‐converted LEDs. This doping of SnCN$_{2}$ proved that a color tuning of the carbodiimide host with different activator ions and the combination of the latter ones is possible. Additionally, as the search for novel high‐performing electrode materials is essential for current battery technologies, this carbodiimide has been investigated concerning its use in lithium‐ion batteries. To further elucidate its application possibilities in materials science, several characterization steps and physical measurements (XRD, in situ XANES, Sn Mössbauer spectroscopy, thermal expansion, IR spectroscopy, Mott‐Schottky analysis) were carried out. The electronic structure of the n‐type semiconductor SnCN$_{2}$ has been probed using X‐ray absorption spectroscopy and density functional theory (DFT) computations