The vibrational spectra of simple cobalt(III) and chromium(III) ammine complexes

Observation of surface‐enhanced Raman scattering for transition‐metal hexaammine cations at the outer Helmholtz plane: Implications for enhancement mechanisms at electrochemical interfaces

Abstract: Surface–enhanced Raman scattering (SERS) has been observed at silver electrodes for several transition‐metal hexaammine complexes even though these cations cannot bind to the metal surface and are excluded from the electrochemical inner layer by the presence of a monolayer of chloride or bromide anions The intensity of the SERS metal‐ammine stretching vibrations νM−N are comparable to those seen for closely related pentammine complexes that are bound to the surface via specifically adsorbed coordinated ligands For hexammineruthenium(III), changes in the νM−N frequency with potential indicate the presence of an interfacial Ru(NH3)3+/2+6 couple The formal potential of this couple obtained from the potential dependence of the SERS intensities is consistent with the Raman scattering ions being located at the outer Helmholtz plane The implications of these results to current models of SERS in electrochemical environments are noted

Vibrational spectra and pseudo-exact force constants of [Ni(NH3)6]2+, [Zn(NH3)4]2+, and [Zn(CN)4]2− with 58Ni/62Ni, 64Zn/68Zn and H/D isotopic substitution

Abstract: The vibrational spectra of [Ni(NH3)6]Cl2, [Ni(ND3)6]Cl2, [58Ni(NH3)6]Cl2, [62Ni(NH3)6]Cl2, [Zn(NH3)4]I2, K2[Zn(CN)4], K2[64Zn(CN)4], K2[(68Zn(CN)4] are reported. Two different methods have been developed which allow to calculate pseudo-exact force constants. It is shown for [Ni(NH3)6]]2+ and [Zn(NH3)4]2+ that reasonable force constants for the skeletons of hexammine and tetrammine metal complexes can be calculated from Raman and infrared data of the isotopically substituted ions using the point mass model, if the isotope shifts can be measured accurately. These force constants are more reliable than previously reported values. In complexes such as [Zn(CN)4]2−, where the ligand and skeletal vibrations are relatively strongly coupled, reliable force constants for part of the force field may under certain conditions be obtained from the “High Low Frequency Separation Method” employing isotopic data.

Raman study of ferric nitrate crystalline hydrate and variably hydrated liquids

Abstract: A Raman investigation on crystalline ferric nitrate enneahydrate (FNEH) has shown that NO3− and Fe(H2O)63+ ions are present in two distinct environments in the monoclinic unit cell of the crystal. In FNEH melt, it has been found that NO3− and Fe3+ ions form a complex in which water is also coordinated to the Fe3+ ion. Raman evidence is presented which indicates that NO3− ion in the nitrate complex is coordinated to the Fe3+ ion in monodentate fashion, with an appreciable covalency in the Fe3+–ONO2− bond. The addition of water to FNEH melt causes dissociation of the nitrate complex. This complex almost ceases to exist when the water content of the melt is raised to 28 mole of water per mole of the salt. A weak polarized band at ∼407 cm−1 in the Fe(NO3)3 · xH2O system (x ≥ 28) has been attributed to the presence of the hydrolysis product of Fe3+ ions. The effect of dilution and of temperature on this band has also been investigated. It is suggested that the hydrolysis product of the salt exists in the form ...

Far infra-red spectra and metal-ligand force constants of metal ammine complexes☆

Abstract: Infra-red spectra of the metal ammine complexes, [M(NH3)6]n+ (M:Co(III), Cr(III) and Ni(II)) and [Cu(NH3)4]SO4·H2O and the halogenoammine Cobalt complexes, trans-[CoX2(NH3)4]+(X:Cl and Br) and [CoX(NH3)5]2+ (X:F, Cl, Br and I), have been measured in the region 4000 cm−1 to 80 cm−1. Vibration assignments have been made at first on an experimental basis, on considering the frequency change with the central metal ion and with the substituted halogen. The infra-red dichroism measurement for trans-[CoCl2(en)2]+ has been also made in order to decide the vibrational modes of trans-[CoX2(NH3)4]+. A normal co-ordinate analysis of these complex ions has been made, including all the ligand atoms, in order to check the vibration assignments made experimentally and to clarify the normal modes of vibration for the observed bands. Force constants associated with the co-ordination bond as well as for the ligand vibrations have been calculated. The values of the metal—nitrogen stretching force constant vary in the sequence: Hg(II) > Co(III) > Cr(III) > Cu(II) > Ni(II) > Co(II). The stretching force constant for the Cobalt—halogen bond is smaller than that for the Cobalt—nitrogen bond, and that for the Platinum (or Palladium)—halogen bond as well.

Infrared spectroscopic study on the co-ordination bond-I: Infrared spectra of cobalt hexammine, pentammine and trans-tetraammine complexes

Abstract: Infrared spectra of [Co(NH3)6]3+, [Co(NH3)5X]2+ (X=F, Cl, Br and I), and trans- [Co(NH3)4X2]+ (X =Cl,Br) have been measured in the 4000-250 cm−1 region. In addition to the characteristic NH stretching and NH3 deformation vibrations, Co—ligand stretching and skeletal deformation vibrations have been observed near 500 cm−1 and near 300 cm−1, respectively. Normal coordinate treatment has been made and the observed frequencies have been quantitatively assigned on the basis of the potential energy distribution and L- matrix. The Co—ligand stretching force constant shows that this co-ordination bond should be appreciably covalent.