Anton M. Heyns

The vibrational spectra of the copper(II) formates: Part II. The internal formate and lattice modes of Cu(HCOO)2·2H2O

Abstract The infrared and Raman spectra of Cu(HCOO) 2 ·2H 2 O and its deuterated analogues have been recorded and the internal formate and lattice modes of these compounds are reported. Some of the internal formate modes reflect the existence of two crystallographically independent formate ions. These ions are arranged in an anti-anti and anti-syn way in the crystal lattice but specific internal formate ions representing the two differently bonded groups do not show large frequency separations, with the exception of the asymmetric CO stretching mode. The fact that the frequency separation between the asymmetric and asymmetris CO stretching modes is significantly larger than in Cu(HCOO) 2 ·4H 2 O and other covalent metal(II) formates, is explained in terms of different CO bond lengths within each formate group. Many of the lattice modes could only be assigned tentatively mainly because of very small isotopic shifts of the formate modes upon deuteration and also because of coupling which occurs between the lattice modes as a result of the low symmetry of the different groups in Cu(HCOO) 2 ·2H 2 O. The librational modes of the formate groups which have a large wagging character, can be assigned with a fair amount of certainty.

Study of the Hydrolysis of Sodium Polyphosphate in Water Using Raman Spectroscopy

Raman spectroscopy is used to monitor hydrolysis of a polyphosphate dissolved in water at pH = 0. It is found that this reaction is of zeroth-order and obeys the Arrhenius equation with Ea = 57 kJ·mole−1. Hydrolysis predominantly takes place at terminal phosphate units, and, although random hydrolysis might be involved in the process, its contribution is shown to be very small with respect to the overall process.

The effect of pressure on the Raman spectra of solids. III. Sodium formate, NaHCOO

The pressure dependence of the Raman bands of NaHCOO has been studied at 298 K and three different phases were identified up to pressures of 30 kbar. Phase II is the one stable at ambient conditions, and when heated to 500 K at ambient pressures it undergoes a transition to phase I. This transition has also been studied and the frequencies of the Raman‐active librations of NaHCOO I resemble those of aqueous solutions of formate ions. From the shifts in the librations which accompany the I–II transition it can be concluded that the Na+–HCOO− interactions are much weaker in phase I than phase II. The Raman spectrum of KHCOO II at ambient conditions is also reported and resemblances between this spectrum and that of NaHCOO III are discussed.

The vibrational spectra of the copper(II) formates: Part III. The vibrations of the water molecules in Cu(HCOO)2 · 2H2O

Abstract The infrared spectra of Cu(HCOO) 2 · 2H 2 O and its deuterated analogues are reported at ambient and liquid nitrogen temperatures. The internal OH modes as well as the librations of the water molecules are discussed and it is shown that the OH and O—D stretching and bending vibrations which have been observed, occur at very low frequencies. This behaviour is explained in terms of the existence of strong hydrogen bonds and also strong copper—water interactions in the crystal. Evans holes are evident in the OH and O—D stretching frequency ranges. The in-plane rocking librations of the water molecules are coupled to the symmetrical OCO bending vibration of the formate groups. The rocking modes and some of the wagging librational modes of the water molecules are positively identified but the twisting modes are only tentatively assigned.

A RAMAN AND INFRARED STUDY OF (NH4)2ZRF6

Abstract The infrared and polarized Raman spectra of diammonium hexafluorozirconate, (NH 4 ) 2 ZrF 6 , are reported over a wide temperature range. It is shown that the Raman spectrum of (NH 4 ) 2 ZrF 6 is characteristic of a compound containing Zr 2 F 12 chains and both ZrF(terminal) and ZrF(bridging) modes have been identified in the ZrF stretching frequency range. The N-D stretching modes of isolated NH 3 D + -ions in the lattice reveal only four distinct absorption peaks at lower temperatures instead of the four quartets predicted. Weak shoulders and the breadth of the infrared bands, however, suggest the presence of an undetermined number of features in the infrared spectra of the isolated NH 3 D + -groups. The NH 4 + -ions, or some of them, display dynamic behavior and the strength of the hydrogen bonds varies from weak to medium/strong and both normal and bifurcated bonds are present in (NH 4 ) 2 ZrF 6 . The changes which occur in the infrared and Raman spectra of (NH 4 ) 2 ZrF 6 upon heating the samples are reported and the final decomposition product ZrO 2 is obtained in a very pure and well-characterized state.

Raman Spectroscopic Investigations of ZrSiO4:V4+, the Blue Zircon Vanadium Pigment

Powdered and single-crystal samples of the vanadium-containing zircon pigment ZrSiO4:V4+ were investigated by means of Raman spectroscopy, the spectra being recorded between 200 and 1100 cm−1 at ambient conditions. V–O vibrational bands could be identified by comparison with spectra of pure ZrSiO4. The possibility of V4+ occupation of the interstitial 8d site withC2hsymmetry was excluded on group theoretical grounds. V—O bond lengths for ZrSiO4:V4+ were estimated to be between 172 and 175 pm from the Raman band wavenumbers; these bond lengths are much shorter than those (204 and 227.6 pm) expected for V4+ on the Zr4+ site, but similar to that for V4+ on the Si4+ site (175.8 pm). This would indicate substitution on the Si4+ site, 4b, rather than the Zr4+ site, 4a. This conclusion is supported by the influence of V4+ and dopants such as Cr4+, Pr4+ and others on the zircon crystal lattice. The changes in the strengths of Si—O bonds with the change of chromophore incorporated into the structure are reflected in the shifts in wavenumber of the Raman-active zircon modes.

The spin-transition complexes [Fe(Htrz)3](ClO4)2 and [Fe(NH2trz)3](ClO4)2 I. FT-IR spectra of a low pressure and a low temperature phase transition

Abstract Infrared spectra of two spin-transition polymers, [Fe(Htrz) 3 ](ClO 4 ) 2 and [Fe(NH 2 trz) 3 ](ClO 4 ) 2 , were investigated. In the structure, the metal centers are bridged through nitrogen atoms in the 1- and 2-positions of the three triazole ligands, each iron being sixfold coordinated to nitrogen. For comparison, Fourier transform infrared (FT-IR) spectra of a similar, but permanently low-spin compound, [Fe(Htrz) 3 ]Cl 2 , and a permanently high-spin compound, [Fe(Htrz) 3 ]SO 4 , were recorded. Mid-infrared spectra indicate bidentate bridging of triazole ligands. Far-infrared spectra of low-spin [Fe(Htrz) 3 ](ClO 4 ) 2 and [Fe(Htrz) 3 ]Cl 2 indicate six equal FeN bonds for the low-spin coordination sphere. Far-infrared spectra of high-spin [Fe(Htrz) 3 ](ClO 4 ) 2 , [Fe(NH 2 trz) 3 ](ClO 4 ) 2 , and [Fe(Htrz) 3 ]SO 4 indicate weakening of all six FeN bonds in the high-spin state, two of the bonds being weakened to a lesser degree than the other four. A low- to high-spin transition is observed for [Fe(Htrz) 3 ](ClO 4 ) 2 upon lowering the pressure to 110 mbar. The low-temperature high- to low-spin transition of [Fe(NH 2 trz) 3 ](ClO 4 ) 2 was investigated by far-infrared spectroscopy.

Vibrational spectra of NaVO3, KVO3 and the solid solutions (Na0.88K0.12)VO3 and (Na0.5K0.5)VO3

Abstract The phase transition in KVO 3 involving changes in the dielectric properties was investigated by means of Raman spectroscopy. A temperature dependence study of the Raman active modes did not reflect the reported changes in the dielectric properties of the compound around 593 K. Infrared and Raman spectra of the two solid solutions, (Na 0.88 K 0.12 )VO 3 and (Na 0.5 K 0.5 )VO 3 are presented in comparison with those of KVO 3 and α-NaVO 3 . The translational modes of the cations could accordingly be identified unambiguously. The frequency dependence of the various vibrational, rotational and translational modes of the VO − 3 chain on composition is also reported and compared to high pressure behaviour of some NH 4 VO 3 vibrations.

An infrared study of the nitro—nitrito linkage isomerization in solid nitro- and nitritopentamminecobalt(III) chloride

Abstract The photochemical isomerization reaction of [Co(NH3)5NO2]Cl2 to [Co(NH3)5ONO]Cl2 has been studied in the solid state by means of i.r. spectroscopy. The reaction is first order with k = 2.53±0.05 × 10−4s−1 and is much faster (t 1 2 =49min) than the well-known spontaneous nitrito → nitro isomerization (t 1 2 = 6 days). The i.r. bands of both the NH3 and ONO− -groups in the range 4000-50 cm−1 indicate minor differences between the structures of freshly and photochemically prepared [Co(NH3)5ONO]Cl2. The far i.r. spectra indicate the disorder existing in the intermediate products during the isomerization processes.

The polymorphism of alkali metal formates—Part I. A Raman study of the II-I transition in NaHCOO

Abstract The II-I phase transition at 500 K in NaHCOO has been studied by means of Raman spectroscopy. X-ray powder diffraction techniques and DTA measurements. The phase transition is of the first-order and the supercooled phase I was obtained and investigated at ambient temperatures. The Raman spectra of phase I can be interpreted in terms of a structure (space group Pc-Cs2) similar to, or even identical with that of NH4HCOO. In this structure the cations are tetrahedrally co-ordinated by four oxygen atoms belonging to four different formate groups. Some crystallochemical trends in the alkali metal formate series are discussed.