Joanne R. Rollo

The use of Raman spectroscopy as a probe for the intermolecular bonding in crystalline tetraphosphorus trisulphide

Abstract The temperature and pressure dependences of the internal and external first-order Raman-active phonons of crystalline α-P 4 S 3 are shown to provide a sensitive probe of the intermolecular bonding. Comparison with a similar study of α-P 4 Se 3 leads to the conclusion that while intra-intermolecular coupling is present, it is weaker in crystalline α-P 4 S 3 . Unlike α-P 4 Se 3 , no rigid layer mode is observed nor is there any softening of the A 1 mode at 440 cm −1 analogous to the 361 cm −1 soft mode of α-P 4 Se 3 . Weak intra-intermolecular coupling is also supported by an analysis of the implicit-explicit contributions to the observed temperature coefficients. A pressure dependent increase in the intensity of the A 1 mode at 440 cm −1 is compared to similar pressure dependent changes in intensity for phonons in other inorganic molecular solids.

An inorganic molecular glass: a glass transition for molecular tetraphosphorus triselenide

Abstract A differential scanning calorimetry study of the phase changes undergone by α′-P 4 Se 3 has resulted in a proposed third orientationally disordered phase, β′-P 4 Se 3 . Undercooling of this disordered β′-phase produces a molecular glass with T g ≅230 K. The glass phase observed when crystalline P 4 Se 3 is cooled from the melt supports the recent claim by Verrall and Elliot that vitreous P 2 Se is a molecular glass.

Phases of tetraphosphorus triselenide analysed by magic angle spinning 31P NMR and Raman spectroscopy, and the Raman spectrum of tetraphosphorus tetraselenide

Abstract The local environments of the cage molecules in the phases of P 4 Se 3 are analysed with 31 P MAS-NMR and Raman spectroscopy. The 31 P MAS-NMR spectra of the orientationally ordered α and α′,-phases have different chemical shifts for the apical P atom (α: 68.0, 86 and 88.0 ppm; α′: 75.8 ppm), but similar chemical shifts for the basal P atoms (α: −58.8 ppm, α′: −60.0 ppm). When either α or α′-P 4 Se 3 is heated above 358 K, the resulting β-P 4 Se 3 has a well-resolved, liquid-like spectrum, indicating extensive molecular re-orientation. The slowly quenched β-phase shows a remnant β-phase mixed with the α-phase as well as P 4 Se 4 . A rapidly quenched sample of β-P 4 Se 3 also shows a small remnant β-phase in the α-phase, but also a new phase with sharp resonances at 12.5, 3.6, 0.1 and −12 ppm. These are probably due to a P 4 Se 4 phase which may be orientationally disordered. The Raman spectrum of P 4 Se 3 heated above the α-β phase transition temperature shows a disappearance of the lattice modes and the 373 cm −1 mode as previously reported, but also shows some decomposition to P 4 Se 4 . The β-phase reverts into the α-phase on quenching, with only weak remnant bands attributable to P 4 Se 4 . The bands of P 4 Se 4 become more prominent as the temperature of the β-phase is raised, but above the β-∂ phase transition they are less prominent. The Raman spectrum of P 4 Se 4 is reported. The strongest band is at 350 cm −1 , with the next strongest band at 185 cm −1 . The spectra indicate that the dominant isomer is the selenium analogue of α-P 4 S 4 ( D 2 h ), confirming previous 31 P MAS-NMR studies.

Temperature dependences of the Raman spectra of the tetraphosphorus triselenodiiodides (α′-P4Se3I2 and β-P4Se3I2) and the tetraphosphorus trithiodiiodides (α-P4S3I2 and β-P4S3I2)

Abstract The Raman spectra of crystalline α′-P 4 Se 3 I 2 , β-P 4 Se 3 I 2 , α-P 4 S 3 I 2 , and β-P 4 S 3 I 2 have been measured as a function of temperature in the range 80–370 K at ambient pressure. In general, the internal and external first-order Raman-active phonons vary smoothly in wavenumber over this temperature interval, a behaviour typical of a molecular solid. Mode softening ( d v d T positive) of the 179.6 cm −1 phonon of β-P 4 Se 3 I 2 is attributed to intra-intermolecular coupling, similar to that observed for the parent molecule P 4 Se 3 .

Raman spectra of the tetraphosphorus trichalcogenide cage molecules P4S2Se and P4SSe2

Abstract Mixtures of the four cage molecules P 4 S x Se 3− x ( x =0, 1, 2, 3) were prepared from α-P 4 S 3 and α- P 4 Se 3 . The Raman-active bands of the mixed chalcogenide molecules have been identified and used together with the results of a normal coordinate analysis to provide assignments for 14 of the 15 normal modes of vibration of P 4 S 2 Se and P 4 SSe 2 . A decrease in wavenumber observed for the most intense Raman-active band of crystalline P 4 SSe 2 with increasing concentration in the mixed solids is attributed to intermolecular SeSe interactions weakening the intramolecular bonds.

The temperature and pressure dependence of the Raman spectrum of crystalline tetraphosphorus decasulphide

Abstract The pressure and temperature dependences of the Raman-active phonons of the molecular crystal P4S10 were investigated. The presence of weak intra-intermolecular coupling is indicated by the softening of the 718.7 and 190.7 cm−1 bands with pressure. Similarities between P4S10 and other phosphorus chalcogenides are thus revealed.