Pn Atoms Research Articles

Attraction versus Repulsion between Methyl and Related Groups: (CH3NHCH3)2 and (CH3SeBr2CH3)2.

The starting point for this work was a set of crystal structures containing the motif of interaction between methyl groups in homodimers. Two structures were selected for which QTAIM, NCI and NBO analyses suggested an attractive interaction. However, the calculated interaction energy was negative for only one of these systems. The ability of methyl groups to interact with one another is then examined by DFT calculations. A series of (CH3PnHCH3)2 homodimers were allowed to interact with each other for a range of Pn atoms N, P, As, and Sb. Interaction energies of these C∙∙∙C tetrel-bonded species were below 1 kcal/mol, but could be raised to nearly 3 kcal/mol if the C atom was changed to a heavier tetrel. A strengthening of the C∙∙∙C intermethyl bonds can also be achieved by introducing an asymmetry via an electron-withdrawing substituent on one unit and a donor on the other. The attractions between the methyl and related groups occur in spite of a coulombic repulsion between σ-holes on the two groups. NBO, AIM, and NCI tools must be interpreted with caution as they can falsely suggest bonding when the potentials are repulsive.

Neutral and Cationic Re(I) Complexes with Pnictogen-Based Coligands and Tunable Functionality: From Phosphorescence to Photoinduced CO Release.

In this work, we have explored Re(I) complexes featuring triphenylpnictogen (PnPh3, Pn = P, As, or Sb)-based coligands and bidentate (neutral or monoanionic) luminophores derived from 1,10-phenantroline (phen), as well as from 2-(3-(tert-butyl)-1H-1,2,4-triazol-5-yl)pyridine (H(N-tBu)). The effect of the increasingly heavy elements on the structural parameters, photoexcited-state properties, and electrochemical behavior as well as the hybridization defects and polarization of the Pn atoms was related to the charges of the main luminophores (i.e., phen vs N-tBu) and explored in terms of photoluminescence spectroscopy, X-ray diffractometry, and quantum-chemical methods. Therefore, an in-depth analysis of the bonding, crystal packing, excited-state energies, and lifetimes was assessed in liquid solutions, frozen glassy matrices, and crystalline phases along with a semiquantitative photoactivation study. Notably, by changing the main ligand from phen to N-tBu, an increase in radiative and radiationless deactivation rates (kr and knr, respectively) at 77 K together with a faster photoinduced CO release and fragmentation at room temperature was detected. In addition, a progressively red-shifted phosphorescence was observed with the growing atomic number of the pnictogen atom, along with a boost in kr and knr at 77 K. Down the Vth main group and upon coordination of the Pn atom to the Re(I) center, an increasingly prominent jump of s-orbital participation on the binding sxp3.00-orbitals of the Pn atoms is evidenced. Based on these findings, the ability of these complexes to act as tunable photoluminescent labels able to perform as light-driven CO-releasing molecules is envisioned.

New layered quaternary BaCu6Sn2As4−x and BaCu6Sn2P4−x phases: Crystal growth and physical properties

We report two new quaternary BaCu6Sn2As4−x and BaCu6Sn2P4−x phases with a new structure type, which are fully characterized by single crystal X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). These two phases crystallize in tetragonal cell with space group I4/mmm (#139) and Pearson symbol tI26. The refined lattice parameters are a = 4.164(1) Å, c = 24.088(3) Å for BaCu6Sn2As4−x, and a = 4.053(2) Å, c = 24.08(1) Å for BaCu6Sn2P4−x, respectively. They possess a distinct layered feature composed of Cu6Sn2Pnx (Pn = P, As) layers sandwiched by the Ba atoms. The Cu-Sn framework of the Cu6Sn2Pnx layer is closely related to the well-known Cu2Sb-type structure, and Pn atoms are found occupying two interstitial sites caused by close packing of Cu and Sn atoms or capped on the top of square nets formed by Cu atoms. The compounds are also characterized by electrical transport measurements down to 2 K.

Compounds of the types Pn(pyS)3 (Pn = P, As, Bi; pyS: pyridine-2-thiolate) and Sb(pyS) x Ph3–x (x = 3–1); molecular structures and electronic situations of the Pn atoms

Abstract The compounds Pn(pyS)3 (Pn = P, As, Sb, Bi) were synthesized from the respective chloride (Pn = P, As, Sb) or nitrate (Bi), pyridine-2-thiol (pySH) and triethylamine (NEt3) as a supporting base in THF (P, Sb), CHCl3 (As) or methanol (Bi). Sb(pyS)3 was also obtained from the reaction of SbCl3 with LipyS (prepared in situ) in methanol. The compounds Sb(pyS)2Ph and Sb(pyS)Ph2 were prepared in a one-pot reaction starting from SbCl3 and SbPh3 (1:1 ratio). Upon Cl/pyS substitution, the resulting reaction mixture allows for a facile separation of the products in hot hexane. P(pyS)3 and As(pyS)3 crystallize isostructurally to the reported structure of Sb(pyS)3 with κ-S-bound pyS ligands. These crystal structures feature close Pn···Pn contacts which are most pronounced for the arsenic derivative. Bi(pyS)3 adopts a different molecular structure in the solid state, which features two chelating (κ 2-S,N-pyS) ligands and a κ-S-bound ligand. The presence of N→Bi interactions between the nitrogen atom of the κ-S-pyS ligand and the Bi atom of another molecule renders this structure a polymer chain along the crystallographic b axis with Bi⋅⋅⋅Bi van-der-Waals contacts. The structures of this set of Pn(pyS)3 compounds were also studied in solution using 1H NMR spectroscopy, revealing equivalent pyS ligands in discrete Pn(pyS)3 molecules. The molecular structure of Sb(pyS)Ph2 was optimized by quantum chemical methods, and a comparison with the structures reported for the other Sb/pyS/Ph combinations reveals Sb(pyS)2Ph to feature the strongest Sb···N interactions with the κ-S-pyS ligand. The results of 1H NMR spectroscopic investigations of the compounds Sb(pyS) x Ph3–x (x = 3–0) suggest the Ph protons in ortho position to be incorporated into intramolecular C–H···S contacts for x = 2 and 1. Natural localized molecular orbital (NLMO) calculations were employed in order to gain insights into the electronic situations of the Pn atoms and Pn–R bonds (R = S, C), especially for the effects caused by formal substitution of Pn in the compounds Pn(pyS)3 and the ligand patterns in the compounds Sb(pyS) x Ph3–x (x = 3–0). For the latter series of compounds, the electronic situation of the Sb atom was further studied by 121Sb Mössbauer spectroscopy, providing a correlation between the calculated electron density at Sb [ρ(0)] and the experimentally observed isomer shift δ. The missing link between group 15 and group 13 metal compounds of the type M(pyS)3, compound Al(pyS)3, was synthesized in this work. In the solid state (confirmed crystallographically), the mer isomer of this tris-chelate complex with distorted octahedral Al coordination sphere was found. This coordination mode was confirmed for the solution state (CDCl3) by 1H and 13C NMR spectroscopy at T = −40 °C.

A first principle study of structural, elastic, electronic and thermodynamic properties of Half-Heusler compounds; YNiPn (Pn=As, sb, and bi)

This article deals with the structural, elastic, thermodynamic, and electronic properties of Half-Heusler compounds; YNiPn (Pn = As, Sb, and Bi). The computations are carried out using the pseudopotential plane-wave method within the generalized gradient approximation (GGA). We have noticed the structural stability in the F-43m phase and lattice constants are well matched with experimental results. The elastic, thermodynamic, and major electronic properties are reported for the first time in these compounds. We have derived the bulk, shear, and Young's moduli of elasticity from the knowledge of elastic constants along with the discussion of mechanical stability and strength of YNiPn. The Cauchy pressure and Pugh's ratio emphasizes ductile nature. From the knowledge of elastic properties, it is observed that the Debye temperature and sound velocities are decreasing from As to Bi. The electronic properties are discussed in terms of band profile, the density of states (DOS), charge density plot, and Fermi surfaces. The electronic band structure and DOS clarify that YNiPn compounds are indirect narrow bandgap semiconductors. The origins of the bandgap in these compounds are interpreted. The charge density plot projects the strong covalent bonding between Ni and Pn atoms while an ionic bonding between Y and Pn atoms. The thermodynamic variables like cell volume, bulk modulus, specific heat, Debye temperature, entropy, Grüneisen parameter, and thermal expansion coefficients have also been analyzed under high pressure and temperature as they are of great technological importance. These compounds are found as potential candidates for thermoelectric materials.

The matching pursuit algorithm revisited: A variant for big data and new stopping rules

Abstract The matching pursuit algorithm (MPA) is used in many applications for selecting the best predictors for a vector of measurements of size n from a dictionary that contains pn atoms, where usually n ≤ pn. A major unsolved problem is to determine the optimal stopping rule. In this work, we investigate various stopping rules which are modifications of the information theoretic (IT) criteria derived for Gaussian linear regression. Because all of them involve the degrees of freedom (df) given by the trace of the hat matrix, we provide some theoretical results concerning this matrix. We also propose novel stopping rules. An important contribution of this paper is a method for computing the df efficiently when big data (n ≫ pn) are processed. The significance of the auxiliary variables appearing in MPA for big data is clarified via a theoretical analysis. The superiority of the new stopping rules in comparison with the traditional approaches is demonstrated in simulations involving big data (n ≫ pn) or overcomplete dictionaries (n

Effect of substitution (Al and P) atoms in ZnO nanosheet on structural and electronic properties

We explore the possibility of formation of two different Aln and Pn atoms (n=1-6) are substitute doped of ZnO nanosheet has been investigated based on ab initio density functional theory. We study the effect of Al and P doping on the structural and electronic properties of a ZnO nanosheet. This study explains the effect of several doping on structural and electronic properties. The results indicate that Al and p substituted on the O site. The binding energy of doped system is negative, implying a stable integration of Al and P. We also found that the least energy gap lies in the Al at two atoms either in P at three atoms. These findings demonstrate that ZnO nanosheet doped of Al and P likely to be applied for various applications such as photocatalytic reactions, optoelectronic, solar cells, etc.

Influence of the elements (Pn = As, Sb, Bi) on the transport properties of p-type Zintl compounds Ba2ZnPn2

In our work, we calculated the relaxation times of Ba2ZnPn2 (Pn=As, Sb, Bi) based on the deformation potential (DP) theory using the first-principles method, and successfully predicted high thermoelectric performance (ZT>2) along z-direction for p-type Ba2ZnAs2 and Ba2ZnSb2. The Seebeck coefficient (S) of Ba2ZnAs2 monotonously increases with increasing temperature, which is favorable for achieving high thermoelectric performance in high temperature range. We also find that the four approximately degenerated bands (Nv=4) near the valence band edge mainly originating from the interaction between Zn atoms and Pn atoms, and the different strengths of ZnPn bonding lead to the different energy range spanned of the four bands. The weak ZnAs bonding decreases the dispersion of the four bands, which leads to a sharply increased total density of states near the valence band edge, and will largely increase the S of Ba2ZnAs2, while the strong ZnBi bonding increases the dispersion of the four bands near the VB edge, which reduces the effective mass of valence bands near the VB edge, and will be in favor of the carrier mobility. The coexistence of two heavy bands and two light bands near the VB edge contributes to their simultaneous high Seebeck coefficients and high electrical conductivities at the optimum carrier concentration. Moreover, their electrical conductivities along the z-direction are much higher than those along the x- and y-directions, possibly originating from the chain-like arrangement of covalent ZnPn4 tetrahedra.

Electronic structure of ZrCuSiAs and ZrCuSiP by X-ray photoelectron and absorption spectroscopy

The electronic structures of quaternary pnictides ZrCuSi Pn ( Pn=P, As) were analyzed by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES). Shifts in the core-line XPS and the XANES spectra indicate that the Zr and Cu atoms are cationic, whereas the Si and Pn atoms are anionic, consistent with expectations from simple bonding models. The Cu 2 p XPS and Cu L-edge XANES spectra support the presence of Cu 1+. The small magnitudes of the energy shifts in the XPS spectra suggest significant covalent character in the Zr–Si, Zr– Pn, and Cu– Pn bonds. On progressing from ZrCuSiP to ZrCuSiAs, the Si atoms remain largely unaffected, as indicated by the absence of shifts in the Si 2 p 3/2 binding energy and the Si L-edge absorption energy, while the charge transfer from metal to Pn atoms becomes less pronounced, as indicated by shifts in the Cu K-edge and Zr K, L-edge absorption energies. The transition from two-dimensional character in LaNiAsO to three-dimensional character in ZrCuSiAs proceeds through the development of Si–Si bonds within the [ZrSi] layer and Zr–As bonds between the [ZrSi] and [CuAs] layers.

Zigzag Chains of Alternating Atoms in A2AuBi (A = Na, K) and K2AuSb. Synthesis, Structure, and Bonding

AbstractThe polar intermetallic phases A2AuBi (A = Na (I), K (II)), and K2AuSb (III) were obtained by direct reaction of the elements at elevated temperatures in niobium ampoules. The three isotypic compounds extend the prominent A2MPn (M = transition metal; Pn = group 15) structure family. Single‐crystal X‐ray diffraction experiments show that these phases (I / II / III) crystallize in the orthorhombic space group Cmcm (No. 63), with a = 9.447(2) / 10.632(2) / 10.450(2) Å; b = 7.700(2) / 7.918(2) / 7.857(2) Å; c = 5.849(1) / 6.597(1) / 6.501(1) Å; V = 425.4(2) / 555.4(2) / 533.8(2) Å3, respectively, and Z = 4. The simple structures, which contain zigzag chains of linear two‐bonded gold atoms and acute angles (64 to 76°) at two‐bonded antimony or bismuth, can readily be rationalized with the Zintl‐Klemm concept. TB‐LMTO calculations show distinct band gaps at EF, and analyses of DOS and COHP curves show optimized Au–Pn bonding, appreciable Au–Au interactions across the chains, and covalent interactions between A and Pn atoms. The observed structural preference over an isoelectronic NaTl type structure, the cation influences, and site coloring were investigated with VASP and EHTB calculations.

Magnetism and Negative Magnetoresistance of Two Magnetically Ordering, Rare-Earth-Containing Zintl phases with a New Structure Type: EuGa2Pn2 (Pn = P, As)

Single crystals of EuGa2Pn2 (Pn = P, As) were grown from a molten Ga flux and characterized by single-crystal X-ray diffraction at 100(1) K. They are isostructural and crystallize in a new structure type (monoclinic, P2/m, a = 9.2822(9) Å, b = 3.8967(4) Å, c = 12.0777(11) Å, β = 95.5220(10)°, R1 = 0.0148, wR2 = 0.0325 (EuGa2P2) and a = 9.4953(7) Å, b = 4.0294(3) Å, c = 12.4237(9) Å, β = 95.3040(10)°, R1 = 0.0155, wR2 = 0.0315 (EuGa2As2)). The structures consist of alternating layers of two-dimensional Ga2Pn2 anions and Eu cations. The anion layers are composed of Ga2Pn6 staggered, ethane-like moieties having a rare Ga−Ga bonding motif; these moieties are connected in a complex fashion by means of shared Pn atoms. Both structures show small residual electron densities that can be modeled by adding a Eu atom and removing two bonded Ga atoms, resulting in structures (<2%) where most of the atoms are the same, but there is a difference in bonding that leads to one-dimensional ribbons of parallel Ga2Pn6 staggered, ethane-like moieties. The compounds can be understood within the Zintl formalism, but show metallic resistivity. Magnetization measurements performed on single crystals show low-temperature magnetic anisotropy as well as multiple magnetic ordering events that occur at and below 24 and 20 K for the phosphorus and arsenic analogs, respectively. The magnetic coupling between Eu ions is attributed to indirect exchange via an RKKY interaction, which is consistent with the metallic behavior. The compounds display large negative magnetoresistance of up to −80 and −30% (MR = [(ρ(H) − ρ(0))/ρ(H)] × 100%) for Pn = P, As, respectively, which is maximal at the magnetic ordering temperatures in the highest measured field (5T).

Neutron diffraction study of magnetic ordering of the manganese bismuth chloro-sulfide: MnBiS 2Cl

In quaternary compounds of Mn 2+ PnQ 2 X ( Pn = Sb, Bi; Q = S, Se; X = Cl, Br, I), Mn atoms in octahedral coordination (4 Q and 2 X) form waved layers separated by Pn atoms. The magnetic structure of the manganese bismuth chloro-sulfide MnBiS 2Cl has been determined by neutron powder diffraction, revealing a magnetic ordering with an incommensurate wave-vector along b-axis ( k = [0, 0.3978, 0]) at 1.6 K. Two modulation models, sinusoidal and helicoidal, give quite equivalent magnetic reliability factors ( R mag = 0.0450 and 0.0481, respectively). The magnetic moment decreases with increasing temperature, to zero at T N = 32 K. The evolution of the propagation wave-vector shows an irregularity at about 28 K. It could evidence two-phase transitions in agreement with the specific heat measurements. These results are compared to those of manganese antimony chloro-sulfide MnSbS 2Cl, isotypic with MnBiS 2Cl.