Tetrahedral P4 Molecules Research Articles

Photolytic Reductive Elimination of White Phosphorus from a Mononuclear cyclo‐P4 Transition Metal Complex

AbstractElemental white phosphorus (P4) is well recognized as a critical precursor to organophosphorus compounds. However, regulatory constraints stemming from the toxic and pyrophoric nature of white phosphorus have significantly limited its accessibility. Herein is described a new approach to white phosphorus storage and release based on a unique example of photolytic reductive elimination of the tetrahedral P4 molecule from a mononuclear cyclo‐P4 molybdenum complex. The latter functions as an air‐stable, chemically‐deactivated source of white phosphorus. The system features efficient photo‐release of white phosphorus using inexpensive violet LED sources. Additionally, high‐yield recapture of unspent white phosphorus by the molybdenum center can be achieved by post‐photolysis heating at convenient temperatures.

Photolytic Reductive Elimination of White Phosphorus from a Mononuclear cyclo-P4 Transition Metal Complex.

Elemental white phosphorus (P4 ) is well recognized as a critical precursor to organophosphorus compounds. However, regulatory constraints stemming from the toxic and pyrophoric nature of white phosphorus have significantly limited its accessibility. Herein is described a new approach to white phosphorus storage and release based on a unique example of photolytic reductive elimination of the tetrahedral P4 molecule from a mononuclear cyclo-P4 molybdenum complex. The latter functions as an air-stable, chemically-deactivated source of white phosphorus. The system features efficient photo-release of white phosphorus using inexpensive violet LED sources. Additionally, high-yield recapture of unspent white phosphorus by the molybdenum center can be achieved by post-photolysis heating at convenient temperatures.

(Super)alkali atoms interacting with the σ electron cloud: a novel interaction mode triggers large nonlinear optical response of M@P4 and M@C3H6 (M=Li, Na, K and Li3O)

Under high-level ab initio calculations, the geometrical structures and nonlinear optical properties of M@P₄ (M=Li, Na, K and Li₃O) and M@C₃H₆ (M=Li and Li₃O) were investigated; all were found to exhibit considerable first hyperpolarizabilities (18110, 1440, 22490, 50487, 2757 and 31776 au, respectively). The computational results revealed that when doping the (super)alkali atom M into the tetrahedral P₄ molecule, the original dual spherical aromaticity of the P₄ moiety is broken and new σ electron cloud is formed on the face of P₄ part interacting with the M atom. It was found that interaction of the (super)alkali atom with the σ electron cloud is a novel mode to produce diffuse excess electrons effectively to achieve a considerable β₀ value. Further, beyond the alkali atom, employing the superalkali unit can be a more effective approach to significantly enhance the first hyperpolarizability of the systems, due to the much lower vertical ionization potential. These results were further supported by the case of the (super)alkali atom interacting with the cyclopropane C₃H₆ molecule with its typical σ aromatic electron cloud. Moreover, the β₀ values of the M@P₄ series are nonmonotonic dependent on alkali atomic number, namely, 1440 au (M = Na) < 18110 au (Li) < 22490 au (K), inferring that the distance between the alkali atom and the interacting surface with the σ electron cloud in P4 is a crucial geometrical factor in determining their first hyperpolarizabilities. These intriguing findings will be advantageous for promoting the design of novel high-performance nonlinear optical materials.

A pathway to diphosphorus from the dissociation of photoexcited tetraphosphorus

We report a computational study of an energetically favorable pathway for the excited-state dissociation of a tetrahedral P4 molecule into two P2 molecules via the simultaneous breaking of four chemical bonds along a highly symmetric (D2d) reaction pathway. Along this pathway, a degeneracy occurs between the first excited state of P4 and the ground state of 2P2 at a lower total energy (ca. 4.7 eV) than the initial state, indicating that the initial photoexcitation provides sufficient energy for the dissociation without significant kinetic barriers. We also found that sequential dissociation of the four P–P bonds exhibits larger activation barriers thus making this a less viable dissociation pathway. Our computational investigation uncovers complicated photochemistry in elemental phosphorus, and suggests a likely mechanism for the environmentally friendly inclusion of phosphorus atoms into organic molecules.

Theoretical study of frequency and temperature dependence of dipole-quadrupole polarizability of P4 and adamantane

The frequency and temperature dependence of dipole-quadrupole polarizability of tetrahedral P4 and adamantane molecules have been studied using first-principle all-electron density functional theory calculation. The recently developed time-dependent auxiliary density functional theory is extended for the calculation of dynamic dipole-quadrupole polarizabilities. Temperature effects are incorporated by Born–Oppenheimer molecular dynamics (BOMD) simulations recorded up to 100ps. The dynamic dipole-quadrupole polarizabilities are calculated along these trajectories. The frequency and temperature effects can be significant for the accurate calculation of dipole-quadrupole polarizability. We have also identified the main reason for the observed discrepancy between experiment and theory in the case of adamantane.

Facile Synthesis of AsP 3

The elements phosphorus and arsenic form tetrahedral P4 and As4 molecules, of which the former is a commodity chemical and the latter unstable. Previously, information on molecules of intermediate composition was limited to a spectroscopic study involving hot gas-phase mixtures of phosphorus and arsenic. The AsP3 molecule has yielded to chemical synthesis and was isolated in solid form as a pure substance with a melting point from 71 degrees to 73 degrees C. Physical properties and spectroscopic characterization data for AsP3 are described, and its structure was determined as a ligand in a coordination complex. Soluble in organic solvents, AsP3 represents an attractive starting point for any synthesis in which the target molecule or material contains an exact 1:3 ratio of arsenic to phosphorus.

Molecular Dynamics Simulations of Liquid Phosphorus at High Temperature and Pressure

By performing ab initio molecular dynamics simulations, we have investigated the microstructure, dynamical and electronic properties of liquid phosphorus (P) under high temperature and pressure. In our simulations, the calculated coordination number (CN) changes discontinuously with density, and seems to increase rapidly after liquid P is compressed to 2.5 g/cm3. Under compression, liquid P shows the first-order liquid-liquid phase transition from the molecular liquid composed of the tetrahedral P4 molecules to complex polymeric form with three-dimensional network structure, accompanied by the nonmetal to metal transition of the electronic structure. The order parameters Q6 and Q4 are sensitive to the microstructural change of liquid P. By calculating diffusion coefficients, we show the dynamical anomaly of liquid P by compression. At lower temperatures, a maximum exists at the diffusion coefficients as a function of density; at higher temperatures, the anomalous behavior is weakened. The excess entropy shows the same phenomena as the diffusion coefficients. By analysis of the angle distribution functions and angular limited triplet correlation functions, we can clearly find that the Peierls distortion in polymeric form of liquid P is reduced by further compression.

Dynamical properties of liquid phosphorus studied by ab initio molecular-dynamics simulations

We have performed ab initio molecular-dynamics simulations for the low-density and high-density liquid phosphorus to investigate their dynamical properties. We have shown that: (i) The vibration modes within the tetrahedral P4 molecules in the low-density molecular liquid can be seen in the calculated velocity autocorrelation function and its spectrum. (ii) A so-called de Gennes narrowing due to the strong spatial correlation between the P4 molecules and phonon peaks are seen in the calculated dynamic structure factors. (iii) The sound velocities estimated from the dispersion relation obtained from the dynamic structure factors are 2100ms−1 for the molecular liquid and 5300ms−1 for the polymeric liquid, which reflect the differences in the density and in the liquid state.

The P(1s) and P(2p) XAFS spectra of elemental phosphorus, theory and experiment

X-ray absorption spectroscopy was used to study the local structure and chemical bonding of elemental phosphorus. Three allotropes of this element exist in the solid state. The most common of these is the amorphous red phosphorus. The other two are crystalline: white phosphorus and black phosphorus. In the gas phase tetrahedral P4 molecules are stable up to ∼ 800 °C. At higher temperatures P2 molecules become dominant.Theoretical P(1s) and P(2p) XAFS spectra of gaseous and solid state phosphorus were calculated by ab initio FEFF and GSCF3 methods. These were compared and the spectral features were related to structural and electronic properties of the different allotropes of elemental phosphorus. The calculation results were then used to explain the features observed in the experimental P(1s) and P(2p) spectra of red phosphorus that were measured using synchrotron radiation.

第一原理計算による高圧分子固体の探究‐液体リンの圧力及び温度誘起相転移

We report constant-pressure first-principles molecular-dynamics simulations on liquid-liquid phase transition of phosphorus. By compressing a low-pressure liquid composed of tetrahedral P4 molecules, a structural transition from a molecular to polymeric liquid (a high-pressure liquid) observed in the recent experiment by Katayama et al. [Nature 403, 170 (2000)] was successfully realized. It is found that this transition is caused by a breakup of the tetrahedral molecules with large volume contraction. The same transition is also realized by heating. This indicates that only the polymeric liquid can stably exist at high temperatures.

The metal-nonmetal transition of liquidphosphorus by ab initio molecular-dynamics simulations

We have carried out ab initio molecular-dynamicssimulations for liquid phosphorus under high temperatureand high pressure in order to investigate the microscopicmechanism of the recently observed liquid-liquid phasetransition of liquid phosphorus. We have successfully shownby our simulation that the structural phase transition withincreasing pressure corresponds to the structural change fromthe molecular liquid composed of stable tetrahedral P4molecules to the polymeric liquid with complex networkstructure and that the calculated structure factors are in goodagreement with those obtained by the x-ray diffractionexperiments. It is also found from our calculated electronicstructure that this structural change gives rise to thenonmetal-metal transition, which is the transition from thenonmetallic molecular liquid to the metallic polymeric liquid.

Superweak complexes of tetrahedral P4 molecules with the silver cation of weakly coordinating anions.

The silver aluminates AgAl[OC(CF3)2(R)]4 (R = H, CH3, CF3) react with solutions of white phosphorus P4 to give complexes that bind one or two almost undistorted tetrahedral P4 molecules in an fashion: [Ag(P4)2]+[Al(OC(CF3)3)4]+ (1) containing the first homoleptic metal-phosphorus cation, the molecular species (P4)AgAl[OC(CH3)(CF3)2]4 (2), and the dimeric Ag(mu,eta2-P4)Ag bridged [(P4)AgAl[OC(H)(CF3)2]4]2 (3). Compounds 1-3 were characterized by variable-temperature (VT) 31P NMR spectroscopy (1 also by VT 32P MAS-NMR spectroscopy), Raman spectroscopy, and single-crystal X-ray crystallography. Other Ag:P4 ratios did not lead to new species, and this observation was rationalized on thermodynamic grounds. The Ag(P4)2+ ion has an almost planar coordination environment around the Ag+ ion due to d(x2 - y2)(Ag) --> sigma*(P-P) backbonding. Calculations (HF-DFT) on six Ag(P4)2+ isomers 4a-f showed that the planar eta2 form 4a is only slightly favored by 5.2 kJ mol(-1) over the tetrahedral eta2 species 4b; eta1-P4 and eta3-P4 complexes are less favorable (27-76 kJ mol(-1)). The bonding of the P4 moiety in [RhCl(eta2-P4)(PPh3)2], the only compound in which an eta2 bonding mode of a tetrahedral P4 molecule has been claimed, must be regarded as a tetraphosphabicyclobutane, and not as a tetrahedro-P4 complex, on the basis of the published NMR and vibrational spectra, the calculated geometry of [RhCl(P4)(PH3)2] (10), the highly endothermic (385 kJ mol(-1)) calculated dissociation enthalpy of 10 into P4 and RhCl(PH3)2 (11), as well as atoms in molecules (AIM) and natural bond orbital (NBO) population analyses of 10 and the Ag(P4)2+ ion. Therefore, 1-3 are the first examples of species containing eta2-coordinated tetrahedral P4 molecules.

Liquid-liquid phase transitions of phosphorus via constant-pressure first-principles molecular dynamics simulations.

Pressure-induced phase transitions in liquid phosphorus have been studied by constant-pressure first-principles molecular dynamics simulations. By compressing a low-pressure liquid which consists of the tetrahedral P4 molecules, a structural phase transition from the molecular to polymeric liquid (a high-pressure phase) observed in the recent experiment by Katayama et al. [Nature (London) 403, 170 (2000)] was successfully realized. It is found that this transition is caused by a breakup of the tetrahedral molecules with large volume contraction. The same transition is also realized by heating. This indicates that only the polymeric liquid can stably exist at high temperature.

A first-order liquid–liquid phase transition in phosphorus

First-order structural phase transitions are common in crystalline solids, whereas first-order liquid-liquid phase transitions (that is, transitions between two distinct liquid forms with different density and entropy) are exceedingly rare in pure substances. But recent theoretical and experimental studies have shown evidence for such a transition in several materials, including supercooled water and liquid carbon. Here we report an in situ X-ray diffraction observation of a liquid-liquid transition in phosphorus, involving an abrupt, pressure-induced structural change between two distinct liquid forms. In addition to a known form of liquid phosphorus--a molecular liquid comprising tetrahedral P4 molecules--we have found a polymeric form at pressures above 1 GPa. Changing the pressure results in a reversible transformation from the low-pressure molecular form into the high-pressure polymeric form. The transformation is sharp and rapid, occurring within a few minutes over a pressure range of less than 0.02 GPa. During the transformation, the two forms of liquid coexist. These features are strongly suggestive of a first-order liquid-liquid phase transition.

Ab initio simulation of the structure and dynamics of white phosphorus (P4) at low temperatures

Ab initio simulations of low-temperature white phosphorus (β-P4) were performed using Car–Parrinello density-functional-theory molecular dynamics and a plane-wave basis set. Gradient corrections to the local density approximation were used to obtain a better description of the weak intermolecular forces. Starting with unit-cell parameters and atomic coordinates recently verified using neutron scattering, molecular dynamics trajectories over 9–10 ps were obtained for temperatures of 50 and 145 K. The computations show that the distortions from ideal tetrahedral P4 molecules found in the reduction of the neutron data may be a finite-temperature effect and not an artifact of the data analysis. Examination of the molecular reorientational dynamics shows that orientational order persists throughout the simulations, which suggests that β-P4 is an orientational crystal.

The radical cation of tetraphosphorus: ESR spectra and structure

X- and Q-band ESR spectra were observed for ˙P4+ cations prepared by exposing solid solutions of P4 in Freon to X-rays or 60Co γ-rays at 77 K; excellent agreement between the observed and simulated spectra revealed that the cations are formed in a D2d‘butterfly’ structure, resulting from the simultaneous cleavage of two bent chemical bonds in the tetrahedral P4 molecule, induced by electron loss.

Crystal Structure of Ordered White Phosphorus(β-P)

Abstract The low-temperature form of white phosphorus (β-P, Ttrans= -76.4°C) is triclinic, P1. The asymmetric unit contains 3 independent tetrahedral P4 molecules. Intramolecular angles are 60 ± 0.5° and the P-P distances are d=220.9(5) pm. The structure of β-P is related to that of γ-Pu, the Pu atoms being substituted by P4.

3p Orbitals, Bent Bonds, and the Electronic Spectrum of the P4 Molecule

The electronic spectrum of P4 has been calculated in the SCF–CI approximation using a 3p atomic orbital (AO) basis. The calculated spectrum is in semiquantitative agreement with that observed in the region 4–9 eV, and this agreement is taken to support the original premise of a 3p AO basis. Earlier work by others suggested that a 3p basis necessarily leads to bent bonds and a bent-bond strain energy. Our calculation predicts that strong pi bonds are present in the molecule, and their presence leads to a resonance which, in turn, vitiates the concepts of ``bend bonds'' and ``strain energy'' in P4. An electron density map is also derived for the valence-shell electrons, and it shows that the regions of highest density are situated symmetrically above each of the triangular faces of the tetrahedral P4 molecule, and, that although arcs of charge are present in the molecule, they do not connect the phosphorus nuclei, as might be expected for bent bonds.

The Tetrahedral P4 Molecule

The Tetrahedral P4 Molecule