Andrew J. Hempleman

F.t.i.r. and Raman spectra of triphenylphosphine, triphenylarsine, triphenylstibine, and dibenzylsulphide

Abstract The f.t.i.r. and Raman spectra of triphenylphosphine, triphenylarsine, triphenylstibine, and dibenzylsulphide in the solid state at ca 80 K have been recorded over the ranges 3500-40 cm−1 (infra-red, 1 cm−1 resolution) and 1650-30 cm−1 (Raman, 2 cm−1 resolution). The data, particularly those in the low wavenumber region, are more extensive, more complete, and of higher quality than those obtained in previous studies. Detailed band assignments are given.

Rhodium-rhodium stretching frequencies in oxygen-16, oxygen-18, and trideuteromethyl derivatives of Rh2(O2CCH3)4(PPh3)2.

Considerable controversy has surrounded previous assignments of rhodium-rhodium stretching frequencies in dirhodium tetracarboxylate complexes. Detailed electronic, infrared, Raman, and resonance Raman studies of /sup 16/O, /sup 18/O and CD/sub 3/ derivatives are presented. Based on this data the nu(RhRh) is at 289.3 cm/sup -1/.

Infrared, resonance Raman, and excitation profile studies of Os2(O2CCH3)4Cl2 and Os2(O2CCD3)4Cl2. The assignment of the osmium-osmium stretching vibration for a complex involving an osmium-osmium multiple bond

Extensive Raman studies (1525-40 cm/sup /minus/1/) of Os/sub 2/(O/sub 2/CCH/sub 3/)/sub 4/Cl/sub 2/ have led to the identification of the three strong bands, /nu//sub 1/, /nu//sub 2/, and /nu//sub 3/, at 229, 393, and 292 cm/sup /minus/1/ to the key skeletal stretching modes, /nu/(OsOs), /nu/(OsO), and /nu/(OsCl), respectively. Raman spectra of the complex at resonance with the intense electronic band at /lambda//sub max/ = 383 nm lead to the development of a six-membered overtone progression in /nu//sub 1/ as well as combination band progressions in /nu//sub 1/ based upon one quantum of either /nu//sub 2/ or /nu//sub 3/. This indicates that the principal structural change attendant upon excitation to the resonant state is along the OsOs coordinate. Fourier transform infrared spectra (3500-40 cm/sup /minus/1/) have also been obtained. Acetate deuteriation provides conclusive evidence for many of the infrared and Raman band assignments. The study provides the first firm identification of /nu/(OsOs) for a multiply bonded species.

Infrared, resonance-Raman, and excitation profile studies of [Os2(O2CCH2Cl)4Cl2], [Os2(O2CC2H5)4Cl2], and [Os2(O2CC3H7)4Cl2]: assignment of osmium–osmium, osmium–oxygen, and osmium–chlorine stretching vibrations

Detailed Raman (1 600–35 cm–1) and Fourier-transform i.r. (3 500–40 cm–1) studies of the diosmium tetracarboxylate complexes [Os2(O2CR)4Cl2](R = CH2Cl, C2H5, or C3H7), coupled with related earlier studies of [Os2(O2CCH3)4Cl2] and [Os2(O2CCD3)4Cl2], have provided a basis for the identification of the three Raman-active (a1g) bands ν1, ν2, and ν3 at 236–228, 393–256, and 311–292 cm–1 respectively, to the key skeletal fundamentals ν(OsOs), ν(OsO), and ν(OsCl), respectively. Thus, while both ν(OsOs) and ν(OsCl) are relatively insensitive to the carboxylate R group, ν(OsO) is, as expected, highly sensitive thereto. Raman studies at resonance with the intense near-ultraviolet electronic band (406–383 nm) of each complex yields resonance-Raman spectra in each case characterised by the development of three overtone progressions in ν1. These reach 6ν1, 4ν1+ν2, and 4ν1+ν3 at most. The results are typical of A-term resonance-Raman scattering. The depolarisation ratio of the ν1 band at resonance with the ca. 390 nm band demonstrates that the latter arises from an axially polarised transition, consistent with an earlier assignment π(Cl)→π*(Os2).

Dirhodium(II,II) tetra-acetate complexes with axially co-ordinated triphenylstibine, triphenylarsine, and dibenzyl sulphide ligands. The syntheses, properties, and X-ray crystal structures of [Rh2(O2CMe)4(SbPh3)2], [Rh2(O2CMe)4(AsPh3)2], and [Rh2(O2CMe)4{S(CH2Ph)2}2]

The triphenylstibine and dibenzyl sulphide complexes [Rh2(O2CMe)4(SbPh3)2] and [Rh2(O2CMe)4{S(CH2Ph)2}2] have been synthesised for the first time, and their electronic and Raman spectra recorded together with those of [Rh2(O2CMe)4(AsPh3)2]. The triphenylstibine complex was isolated as light brown crystals belonging to space group P, with one centrosymmetric molecule per unit cell. The structure has been refined to an R value of 0.027 for 3 608 observed intensities measured on a diffractometer. The triphenylarsine complex was isolated as maroon needles also belonging to space group P with one centrosymmetric molecule per unit cell. The structure has been refined to R 0.022 for 2 969 observed intensities. The dibenzyl sulphide complex crystallises as burgundy-coloured thin plates with two centrosymmetric molecules per unit cell, space group P21/c. The final R value was 0.056 for 2 469 observed intensities. The dirhodium tetra-acetate nuclei in the three complexes are essentially identical with each other and with the nuclei found in analogous bis adducts. The Rh–Rh bond lengths are 2.421 (4), 2.427(1), 2.406(3)A for the triphenylstibine, triphenylarsine, and dibenzyl sulphide complexes, respectively, and the Rh–Sb, Rh–As, and Rh–S bond lengths are 2.732(4), 2.576(1), and 2.561(5)A, respectively. The Rh–Sb distance is the longest (by 0.13 A) axial rhodium-to-donor-atom bond length known for a bis adduct of dirhodium tetra-acetate. The syntheses of these complexes further demonstrate the versatility of the dirhodium tetra-acetate nucleus in co-ordinating a wide variety of different axial ligands.

Infrared, Raman and pre-resonance Raman spectroscopy of Rh2(O2CCH3)4(S(CH2Ph)2)2

Abstract The infrared (3500-40 cm −1 ), Raman and pre-resonance Raman spectra (3150-20 cm −1 ) of the complex Rh 2 (O 2 CCH 3 ) 4 (S(CH 2 Ph) 2 ) 2 have been studied in detail at ca. 80 K and compared with those of other dirhodium tetraacetate complexes. Assignments for the key skeletal modes, ν 1 [ν(RhRh)] and ν 2 [ν(RhO)], are given. Although resonance conditions could not be reached, owing to the short wavelength (290 nm) of the first allowed electronic transition of the complex, pre-resonance effects are evident from the substantial enhancement of both ν 1 and (especially) ν 2 with 363.8-nm excitation. The ν 1 value is in line with that expected on the basis of the previously established reciprocal relationship between the wavenumber of the rhodiumrhodium stretching fundamental and the rhodiumrhodium bond length.

Infrared, Raman, and resonance-Raman spectra of [Mo2(O2CCH3)4] and [Mo2(O2CCD3)4]

The i.r., Raman, and resonance-Raman spectra of [Mo2(O2CCH3)4] and [Mo2(O2CCD3)4] over the range 3 100–50 cm–1 have been measured, and the bands assigned. The band shifts on deuteriation are discussed in detail. In particular, ν(Mo–Mo) at 404 cm–1 is insensitive (as expected) to deuteriation, but the wavenumbers of many other modes [apart from the obvious ν(CH), CH3 deformation, and rocking modes], viz.ν(CC), ρr(COO), and δ(OCO), are sensitive to deuteriation. This implies extensive coupling of the ring co-ordinates. Raman spectra at resonance with transitions in the violet and ultraviolet display short overtone and combination-band progressions involving ν(Mo–Mo), ν(Mo–Mo), and ρr(COO) which indicate that the geometric changes on excitation occur all around the Mo–O–C–O–Mo rings but are small along any one co-ordinate.