Systematic structural studies on cobalt(II) complexes of tricyclohexylphosphine oxide and related ligands

The new cobalt(II) phosphine oxide complexes Co(Cy₃PO)₂Cl₂ (1), Co(Cy₃PO)₂Br₂ (2), Co(Cy₃PO)₂I₂ (3), Co(Ph₂CyPO)₂Cl₂ (4), Co(Ph₂CyPO)₂Br₂ (5), Co(Ph₂CyPO)₂I₂ (6), Co(Ph₂EtPO)₂Br₂ (7), Co(Cy₃PO)₂(NCS)₂ (8) and Co(Cy₃PO)₂(NO₃)₂ (9) have been prepared mainly by the reaction of anhydrous CoX₂ (X = Cl, Br, I, NCS, NO₃) with the appropriate phosphine oxide. The complexes were characterised by single-crystal X-ray crystallography supported by IR and UV-Vis absorption spectroscopy. The structural analyses show that the cobalt(II) centre adopts a distorted tetrahedral coordination geometry except for 9 which displays an octahedral geometry. Systematic structural features of these complexes are explained within this paper.     

The absorption spectrum of phosphine (PH3) between 2.8 and 3.7 μm: Line positions, intensities, and assignments

Over 8000 line positions and intensities of phosphine (PH₃) at 3 μm have been measured at 0.0115 cm⁻¹ resolution with the McMath-Pierce Fourier Transform spectrometer at Kitt Peak. The observed line intensities ranged from 4.13 × 10⁻⁶ to 4.69 × 10⁻² cm⁻² atm⁻¹ at 296 K, for line positions between 2724.477 and 3601.652 cm⁻¹. This region spans eight interacting vibrational states: 3ν₂ (2940.8 cm⁻¹), 2ν₂ + ν₄ (3085.6 cm⁻¹), ν₂ + 2ν₄ (3214.9 cm⁻¹), ν₁ + ν₂ (3307.6 cm⁻¹), ν₂ + ν₃ (3310.5 cm⁻¹), 3ν₄ (∼3345 cm⁻¹), ν₁ + ν₄ (3426.9 cm⁻¹), and ν₃ + ν₄ (3432.9 cm⁻¹). Assignments have been determined for all the bands except 3ν₄ (a weak band in a highly congested area) for a total of 4232 transitions. The total integrated intensity for this region is 5.70 cm⁻² atm⁻¹ near 296 K, and assigned lines account for 79% of the observed absorption. The two strongest bands in the region are ν₁ + ν₄ and ν₃ + ν₄ with band strengths at 296 K of 1.61 and 2.01 cm⁻² atm⁻¹, respectively. An empirical database of PH₃ line parameters (positions, intensities, and assignments) is now available. Lower state energies (corresponding to assignments from this study) and line widths from the literature are included; default values are used for unassigned features.     

Phosphine-functionalised polymer resins as Pd scavengers

Three phosphine-functionalised polymer resins were used as scavengers of palladium catalysts from Buchwald-Hartwig aryl amination reactions. The purity of the products was assessed, and residual palladium analysed by ICP-AES. Scavenging efficiencies of up to >98.5% were demonstrated.     

A three-dimensional network structure built from selenodiphosphate(IV) and copper selenide tetrahedral building blocks: K3Cu3P3Se9

The reaction of red phosphorus, potassium polyselenide, and copper metal at moderate temperatures yields K₃Cu₃P₃Se₉. The structure was determined by single crystal X-ray diffraction (P2₁/c, a = 8.741(2) Å, b = 10.774(2) Å, c = 20.033(3) Å, β = 92.96(2)°). The structure consists of [P₂Se₆]^4?-anions that link [CuSe₄] tetrahedra in an open, three-dimensional, framework structure. A Valence Electron Concentration treatment of this structure reveals six different primary tetrahedral building blocks.     

N2-broadening coefficients in the ν2 and ν4 bands of PH3

N₂-broadening coefficients are measured for 61 transitions of PH₃ in the ^QR branch of the ν₂ band and the ^PP, ^RP, ^SP, and ^PQ branches of the ν₄ band, using a tunable diode-laser spectrometer. The recorded lines with J values ranging from 1 to 16 and K from 0 to 11 are located between 1008 and 1106 cm⁻¹. The collisional widths are determined by fitting each spectral line with a Voigt profile, a Rautian profile, and a speed-dependent Rautian profile. The latter models provide larger broadening coefficients than the Voigt model. These coefficients have also been calculated on the basis of a semiclassical model of interacting linear molecules by considering an atom-atom Lennard-Jones potential in addition to the electrostatic contributions. The theoretical results are in good agreement with the experimental data and reproduce the J dependence of the broadenings, but their decrease at high J values is overestimated for the ^QR (J, K) transitions.     

Chromatographic determination of phosphine (PH3) and hydrogen sulfide (H2S) in the headspace of anaerobic bacterial enrichments using flame photometric detection

Summary A gas chromatographic method is presented which distinguishes phosphine from hydrogen sulfide and other possible headspace gases of anaerobic microbial cultures. In anaerobic cultures spiked with phosphine, this gas is recovered in the liquid and gaseous phase down to 10 pg per ml of gas or liquid. No biogenically produced phosphine was found. Phosphine in amounts as small as 30 ng per 1 can be stored for several days in glass bottles covered with rubber septa, filled with nitrogen, in the presence or absence of water or of an anaerobic bacterial culture. Due to the selectivity of the detector and the retention characteristics of the porous layer open tubular polymer column alkanes, alkenes and organosulfur compounds routinely found in anaerobic bacterial headspaces do not interfere with the analytical quantification of phosphine.     

Ohmic Contacts to ZnSe-Based Materials

The formation of ohmic contacts to n- and p-type ZnSe is reviewed. The mechanisms for forming reasonable low-resistance ohmic contacts to n-ZnSe are well understood. This results from the fact that the Fermi energy level of ZnSe is unpinned and metals with sufficiently large work functions can make contact to n-type material. However, the situation is reversed for p-ZnSe where a large band gap and large electron affinity make it impossible to find metals with sufficiently large work functions to create an ohmic contact. Instead, the use of HgSe to form low barrier height Schottky contacts and of ZnSe/ZnTe multiple quantum wells (MQWs) to form ohmic contacts is reviewed. Although the MQWs can be used to form ohmic contacts to p-ZnSe, they degrade at high temperatures and high current densities. This is reviewed and shown to be a serious problem for applications to laser diodes.     

Synthesis of glyoxylyl peptides using a phosphine labile α,α′-diaminoacetic acid derivative

We describe in this letter the preparation of a novel protected α,α′-diaminoacetic acid derivative that acts as a masked glyoxylic acid equivalent. The reagent could easily be introduced on a peptide chain using standard Fmoc/tert-butyl solid-phase methods and resisted to the TFA treatment allowing the deprotection and cleavage of the peptide. Unmasking of the glyoxylyl group was performed in solution in the presence of a phosphine.