Spectroscopic assignments of the excited states of trans-(N2)2M(Ph2PCH2CH2PPh2)2(M = W, Mo)

Abstract

infrared spectrum reported by Barrowcliffe et al.25 Further, formally forbidden modes appear in the infrared spectrum of CszIn11'o,5SbVo,5C16, but in this case their intensity is independent of temperature." It was postulated that the space group of both compounds is lower than Fm3m and that CszSbC16 might undergo a phase change as the temperature is lowered resulting in increased localization of the two S b valencies in the crystal, in contrast to the mixed-metal In"',Sbv salt which shows no evidence of such a transition.We have found that CszSbC16 shows superlattice ordering of SbC163-and SbC16-and the space group is M,/amd. Sb"' and SbV occupy sites of symmetry D2d, no longer possessing a center of inversion. Taking into account the descent in symmetry from an 0, site to a D2d site, we find that uz and u5 should become infrared active. Indeed, u2v, ugV, and vJ1" are observed in the infrared spectrum of CszSbC16. The appearance of ulV and vll'I cannot be explained by using the site-group symmetry properties. Further, u3 and u4 become Raman active and this might explain the appearance of ujV in the resonance Raman spectrum.In the primitive unit cell of Cs2SbC16, there are two Sb111C163-and two SbVC16-ions, the full factor-group symmetry being D4,,, which possesses a center of inversion. The symmetries of the vibrational modes at the zone center involving the Sb"'Cls3-and SbVC16-units can be obtained by the method of ascent in symmetryZ7 whereby a representation of a subgroup (i.e. Dzd) can be correlated with those representations of the supergroup (i.e. D4*) that are obtained as ascent in symmetry. However, even allowing for the full factor-group symmetry, it is not possible to account for the appearance of ullI1 and ulV in the infrared spectrum of CS2SbC16. (27) Boyle, L. L. Acta Crystallogr., Sect. A 1972, A28, 172. (28) Tovborg-Jensen, A.; Rasmussen, S . E. Acta Chem. Scand. 1955,9,708.We have also studied the evolution of the structure of CszM1l10 3 b V o ,Cl, (M = Sb, Bi, T1) with temperature. No evidence of a phase transition is apparent between 5 and 423 K. The structure is tetragonal a t all temperatures, and the only effect present is that of thermal expansion (approximately isotropic). The tetragonal distortion measured by the c/a ratio is effectively constant as are the DZd distortions of the individual SbVC16-and Sb111C163-ions. Hence the change in intensity of the "forbidden" peaks in the infrared spectrum does not seem to arise from a corresponding evolution of the crystal structure. It is worth noticing that similar "forbidden" peaks, though temperature independent, appear in the infrared spectrum of CszInl*10 5Sbvo 5C16, whose structure is strictly cubic at low temperatures. The SbvCl, and In"'Cls3-ions are constrained by symmetry to be octahedral in this case. Thus it seems more plausible that the origin of these "forbidden" peaks may lie in the involement of vibrational modes away from the Brillouin zone center." Such phonon dispersion may result in the breakdown of the selection rules. Furthe...

The Effect of the Diphosphine Basicity on the Excited-State Properties of trans-(N2)2W(R2PCH2CH2PR2)2: Identification of Near-Degenerate, Luminescent 3MLCT and 3LF Terms

“…Lifetime versus temperature profiles for the three complexes are shown in Figure . Data for the 4-Ph−H complex agree with those measured previously by Brummer and Crosby …”

“…This spacing is too high to be assigned to a W−P stretching mode but is similar to the 555-cm -1 (Nujol mull) infrared band observed for each complex that has been assigned to a W−N stretching mode . It is also similar to the totally symmetric resonance at 525 ± 3 cm -1 observed in the Raman spectrum of the 4-H−Ph complex (298 K, C 6 H 6 ) . We tentatively assign the vibronic structure on the emission bands to a W−N stretching mode coupled to the b 2g ← a 1g electronic transition.…”

A Photochemical Activation Scheme of Inert Dinitrogen by Dinuclear RuII and FeII Complexes

“…[78,79] for a mechanistic study on photochemically induced N 2 loss from trans-[(N 2 ) 2 W(dppe) 2 ] with dppe = 1,2-bis-diphenylphosphinoethane); the excited states of this complex were later assigned by Brummer and Crosby. [80] Such side processes might be overcome by the use of a tailored laser wavelength in order to exactly meet the excitation energy for the S 0 !S 1 transition.…”

Nature of the lowest emitting states of trans-(N2)2W(dppe)2

“…A complete report of this study, including spectroscopic data on inz«s-(N2)2Mo(dppe)2 and symmetry assignments of the lowest states of the tungsten molecule, will be published elsewhere. 5…”