D.B. Powell

Vibrational spectra of carboxylato complexes—III. Trinuclear ‘basic’ acetates and formates of chromium(III), iron(III) and other transition metals

Abstract The i.r. and Raman spectra of a series of complexes [M III 3 O(OOCR) 6 L 3 ]X· x H 2 O (M = Cr, Fe, Mn, Ru, Rh; L = H 2 O, pyridine, γ-picoline; X = Cl, Br, I, NO 3 , ClO 3 , ClO 4 , BF 4 ) have been analysed in detail. The vibrational modes of the central M 3 O and the three surrounding MO 4 units, are identified. The metal—nitrogen stretching vibrations and the MOH 2 modes are assigned. The ‘basic’ chromium(III) formate is shown to be [Cr 3 O(OOCH) 6 (OH 2 ) 2 (OOCH)] x H 2 O, containing monodentate, inner-sphere coordinated formate ion. The use of the symmetric and asymmetric OCO stretching frequencies in characterizing bridging carboxylate ions is discussed.

Vibrational spectroscopic characterisation of hydrogen bridged between metal atoms: A model for the adsorption of hydrogen on low-index faces of tungsten

Abstract Vibrational spectra of hydrogen chemisorbed on metal surfaces are discussed in the context of data from model cluster compounds and adsorption sites for hydrogen on low index planes of tungsten are suggested on the basis of reported electron energy loss spectra. A hydrogen adsorption site bridging two metal atoms is proposed for both the low coverage, β 2 , and the high coverage, β 1 , states of hydrogen on W(100) and the change in the symmetric metal-hydrogen stretching frequency is correlated with the reconstruction of the tungsten surface in the β 2 state.

Infrared and Raman spectra and the vCC stretching frequencies of some silver-olefin and platinum-olefin complexes

Abstract Raman spectra of aqueous solutions of some silver-olefin complexes and the i.r spectrum of a new platinum-olefin complex, [PtCl 2 (Me 2 CCMe 2 )] 2 , have been studied in an attempt to enlarge upon a recent suggestion that v CC in platinum-olefin complexes could be preferably assigned to a Raman band in the 1240 cm −1 region rather than at about 1500 cm −1 . We conclude that while it is possible to assign the 1240 cm −1 band in the platinum-ethylene complex to a mainly CC stretching vibration in the complexes with substituted olefins the 1500 cm −1 band should be assigned to a mainly CC stretching mode. However both these statements are over simplications, and the true situation is best discussed in terms of the percentage charge of each frequency on complex formation. The summed percentage charges give the best spectroscopic measure of the modification of the CC bond.

Vibrational spectra and the force field of ethylidyne tricobalt nonacarbonyl: analogies with spectra from the chemisorption of ethylene upon the Pt (111) crystal face

A detailed vibrational analysis is reported for CH3CCo3(CO)9 and for its deuterated analogue, and assignments have been confirmed by means of an approximate normal-coordinate analysis. Some significant revisions of an earlier assignment have been made. Comparison of these spectra with those obtained by electron energy-loss spectroscopy of a species resulting from the chemisorption of acetylene and ethylene on Pt (111) above 300 K supports the identification of the latter as containing a C·CH3 group. The two most probable alternatives are a CH3CHPt2 species or CH3CPt3+adsorbed hydrogen atoms.

Low-frequency vibrational spectra of triphenylphosphine and triphenylarsine complexes of d10 gold(1) and Ni(0)

Abstract The low frequency i.r. and Raman spectra have been obtained in the solid state of complexes of triphenylphosphine and triphenylarsine, Ni L (CO) 3 and Au L Cl(Br), [ L = (C 6 H 5 ) 3 P and (C 6 H 5 ) 3 As]. Raman polarisation data have also been obtained in solution. A vibrational assignment has led to the identification of metal—phosphorous and metal—arsenic stretching modes which have been compared with those of related phosphine complexes where L = PH 3 , P(CH 3 ) 3 and PF 3 .

Vibrational spectra of carboxylato complexes—I. Infrared and Raman spectra of beryllium(II) acetate and formate and of zinc(II) acetate and zinc(II) acetate dihydrate

Abstract The spectra of the title compounds have been recorded and interpreted. On this basis, the structures of the anhydrous compounds Be(OOCH) 2 , Be(OOCMe) 2 , Zn(OOCMe) 2 are predicted to have tetrahedral coordination with the carboxylate ions acting as bidentate ligands.

Vibrational spectra of carboxylato complexes—IV. Mixed-metal and mixed-valence oxo-trinuclear complexes

Abstract Infrared spectra of mixed-metal complexes [Cr 3- n Fe n O(OOCR) 6 L] + ( n = 1,2; R = H, CH 3 ; L = H 2 O, γ-picoline, pyridine), and of mixed-valence complexes [Fe III 2 Fe II O(OOCCH 3 ) 6 py 3 ], [Ru III 2 Ru II O(OOCCH 3 ) 6 L 3 ] (L = H 2 O, P(C 6 H 5 ) 3 ) are reported and compared with analogous symmetrical (Cr III ) 3 , (Fe III ) 3 and (Ru III ) 3 species. The effects of lowered symmetry are seen in the mixed-metal but not in the mixed-valence complexes.

Internal rotation of XH3 groups in the solid state

Abstract The infrared spectra of a number of solid compounds with coordinated NH3 and CH3 groups have been studied at temperatures from 90°K to 470°K. The changes observed in the band contours are considered in relation to the rotation of XH3 groups relative to the rest of the molecule. Compounds examined as KBr discs were trans [Pd(NH3)2X2]° (X  Cl or 1), and their deuterium analogues, and Au2I2(CH3)4. The latter compound has also been examined in solution and similar band contours were obtained to those in the solid state. The band contours of the perpendicular (E) vibrations have been compared with the calculated contours for free rotation and estimates of the Coriolis coupling constants have been made. Applying the procedure used by Bulanin and OrlovA for diatomic molecules in solution, potential barriers to internal rotation have been calculated for Pd(NH3)2I2 and Pd(NH3)2Cl2.

The M–H bond stretching frequencies of µ2-bridged metal hydrides and their relationship to the M–H–M interbond angle

A successful theoretical correlation is made of experimental data on the M–H bond stretching modes of µ2-bridged metal hydrides with the M–H–M interbond angle, based on the application of central or valence force field to the MHM unit.

[(η2-C2H4)Os(CO)4] as a vibrational model for type I′ ethene chemisorbed as a metallacyclopropane on metal surfaces

A comprehensive vibrational assignment of the hydrocarbon features in the infrared and Raman spectra of (η2-C2H4)Os(CO)4 has been achieved with the help of data from the (13C2H4) and (C2D4) isotopologues. Close analogies with the vibrational spectra of thiirane (ethene sulfide) assist in the assignment and emphasize the metallacyclopropane nature of the (C2H4Os) group. Comparisons are made with analogous spectra from (η2-C2H4)Fe(CO)4 and from Zeises salt, K[(η2-C2H4)PtCl3].Taking into account the metal–surface selection rule associated with on-specular vibrational electron energy loss or reflection–absorption infrared spectra, good agreement is found between the wavenumber/intensity pattern from the a1 modes of the complex and from ethene chemisorbed on metal surfaces previously designated Type I′.