D. Stoilova

Infrared study of some synthetic phases of malachite (Cu2(OH)2CO3)–hydrozincite (Zn5(OH)6(CO3)2) series☆

Synthetic malachite, hydrozincite and five monophasic mixed copper-zinc hydroxycarbonates have been studied by Fourier transform infrared (FTIR) spectroscopy at ambient and liquid nitrogen temperature in the region of 4000-400 cm(-1). The analysis of the spectra reveals that the samples containing up to 20% zinc retain the malachite lattice, thus forming solid solutions. The inclusion of zinc ions in malachite reflects on the positions and intensity of the bands corresponding to the internal modes of the carbonate ion, to the OH librations and to the Me-O interactions. For example, the higher and the lower frequency components of v3 shift to higher and lower frequencies, respectively. The intensity of the bands corresponding to v2 decreases with the zinc content increase. The spectrum of the sample Cu1.31Zn0.69(OH)2CO3 become diffuse and ill-resolved in the region of the Me-O interactions (region below 600 cm(-1)) and the corresponding bands are shifted to lower frequencies due to the weaker Zn-O interactions as compared with those of the copper ions. The internal modes of the carbonate ions in hydrozincite and aurichalcite are assigned and discussed taking into account the site symmetry and factor group symmetry. The OH and OD stretches (matrix-isolated HDO molecules) and the hydrogen bond strengths are interpreted in terms of Me-O interactions (synergetic effect), hydrogen bond angles and different hydrogen bond acceptor strengths of the oxygen atoms from the carbonate ions. It proves that the hydrogen bonds in hydrozincite are stronger as compared with those in malachite, irrespective of both the larger hydrogen bond lengths and the weaker Zn-O interactions in hydrozincite due to the higher hydrogen bond acceptor strength of the non-coordinated oxygen atom and the formation of bifurcated hydrogen bonds.

Infrared and Raman studies of the solids in the Mg(CH3COO)2–Zn(CH3COO)2–H2O system

Abstract The infrared and Raman spectra of Mg(CH3COO)2·4H2O, Zn(CH3COO)2·2H2O and the double salt MgZn(CH3COO)4·4H2O have been recorded and discussed with respect to the internal modes of the acetate ions and the water molecules. MgZn(CH3COO)4·4H2O crystallizes in the triclinic system with lattice parameters: a=10.441(3) A , b=10.353(3) A , c=8.949(3) A , α=105.67(2)°, β=114.77(2)°, γ=77.52(2)°, V=839.8(3) A 3 . The analysis of the spectra of MgZn(CH3COO)4·4H2O reveals the existence of probably at least three crystallographically non-equivalent acetate ions in the lattice. The strength of the hydrogen bonds in the three salts is studied by the method of IR matrix spectroscopy (matrix-isolated HDO molecules). The frequencies of the OD modes reveal that the acetate oxygens are stronger hydrogen bond acceptors than the water oxygens and the non-coordinated acetate oxygens show stronger acceptor abilities as compared to that of the coordinated ones. Comparatively strong hydrogen bonds are formed in Zn(CH3COO)2·2H2O. The number of the bands corresponding to the uncoupled OD vibrations in MgZn(CH3COO)4·4H2O evidences that at least four crystallographically different water molecules are expected to exist in the lattice. The water librations in the salts under study are also discussed.

Raman and IR study of cobalt acetate dihydrate

Abstract The Raman spectra in the region 40–3800 cm−1 and the IR spectra in the region 400–4000 cm−1 of cobalt acetate dihydrate (CADH) have been studied and compared to the corresponding spectra of cobalt acetate tetrahydrate (CATH). Spectral information on the existence of two different acetate ions in the lattice of CADH has been derived and some suggestions about the nature of the acetate groups and water molecules in the crystal have been put forward.

Vibrational behavior of the SO stretches in compounds with kröhnkite-type chains Na2Me(SeO4)2·2H2O with matrix-isolated SO42− and Me′2+ guest ions (Me = Mn, Co, Ni, Cu, Zn, Cd)

Abstract The infrared spectra of related compounds with krohnkite-type chains Na 2 Me(SeO 4 ) 2 ·2H 2 O (Me=Mn, Co, Ni, Cu, Zn, Cd) containing matrix-isolated SO 4 2− guest ions are reported and discussed with respect to the SO stretching modes ν 3 and ν 1 . Due to the low site symmetry C 1 of the SO 4 2− guest ions three bands for ν 3 and one band for ν 1 are seen in all spectra. When SO 4 2− guest ions are incorporated in the triclinic Na 2 Zn(SeO 4 ) 2 ·2H 2 O, Na 2 Co(SeO 4 ) 2 ·2H 2 O and Na 2 Ni(SeO 4 ) 2 ·2H 2 O host lattices the ν 3 stretching region resembles a higher local symmetry (A 1 ⊕E) of the SO 4 2− guest ions than the crystallographic one (i.e. Δ ν ab >Δ ν bc instead of Δ ν ab ≈Δ ν bc , a, b and c being three ν 3 components). Hence, the ratio between Δ ν ab and Δ ν bc additionally to Δ ν max (the difference between the highest and the lowest wavenumbered SO stretching modes) has to be taken into account when the SO 4 2− guest ion distortions are considered (the higher the ratio Δ ν ab /Δ ν bc is, the weaker the distortion is). Both the site group splittings of the triplet component ν 3 (Δ ν ac ) and Δ ν max values are an adequate measure for the SO 4 2− guest ion distortion when the guest ions are incorporated in the monoclinic Na 2 Cu(SeO 4 ) 2 ·2H 2 O, Na 2 Mn(SeO 4 ) 2 ·2H 2 O and Na 2 Cd(SeO 4 ) 2 ·2H 2 O (i.e. Δ ν ab ≈Δ ν bc ). In addition to the local potential at the lattice site of the host lattice, the metal environment of the SO 4 2− guest ions reflects on the guest ion distortions. A correlation between the SO 4 2− guest ion distortions and the metal electronic configurations has been found and discussed. Me′ 2+ guest ions incorporated additionally to the SO 4 2− guest ions in the selenate lattices do not influence practically on the vibrational behavior of the SO stretches.

Infrared study of νOD modes in isotopically dilute (HDO) kieserite-type compounds MXO4·H2O (M=Mn, Co, Ni, Zn, and X=S, Se) with matrix-isolated M′2+ and X′O42− guest ions

Abstract The hydrogen bond strength in kieserite-type sulfate and selenate monohydrates has been studied by the method of double-matrix spectroscopy. The infrared spectra of isotopically dilute (matrix-isolated HDO molecules) kieserite-type compounds MXO 4 ·H 2 O (M=Mn, Co, Ni, Zn, and X=S, Se) with matrix-isolated X′O 4 2− and M′ 2+ guest ions are presented and discussed in the region of the OD stretching modes. The OD frequencies indicate that the compounds under investigation form comparatively strong hydrogen bonds. The frequency shifts of the uncoupled OD stretching modes of the HDO molecules within the isostructural series and those influenced by the guest ions, and the strength of the hydrogen bonds formed, are discussed in terms of the respective O w ⋯O distances, which hint at stronger hydrogen bonds for the sulfate series than for the selenate one by mistake, the larger hydrogen bond acceptor capability of SeO 4 2− ions compared to SO 4 2− ones, the different metal–water interactions and repulsion potentials of the lattice, and the reorientation of the water molecules caused by the guest ions. The shifts of the OD stretches of the OD⋯OSe′O 3 bonds (Se′O 4 2− matrix isolated) to the lower wavenumbers as compared to the parent selenates are caused by the reorientation of the hydrate water molecules and strengthening the hydrogen bond to the stronger acceptor and vice versa. When smaller metal ions having smaller M–OH 2 bond lengths and, hence, stronger synergetic effect replace larger ones, the OD stretches are shifted to lower wavenumbers as compared to those due to the host M–O w ⋯O bonds and vice versa.

Raman study of complexation in aqueous solutions of magnesium acetate

Abstract Raman spectra of aqueous solutions of magnesium acetate at 293 K have been studied in the concentration range 0.65–3.24 M, as have the Raman spectra of the crystallohydrate Mg(CH 3 COO) 2 ·4H 2 O. Fourier deconvolution and band fitting techniques have been used to analyse the spectra in three characteristic regions. The gradual evolution of two new components, in addition to the component corresponding to the CC vibration of the free acetate ion, is observed in the CC region of the solutions. These are identified as belonging to mono- and bisacetato complexes. In saturated solutions the bisacetato complexes are the dominating metal-ligand species. Their presence is confirmed also by Fourier deconvolution of the in-plane rocking CO 2 vibration.

Infrared study of νOD modes in isotopically dilute (HDO) isostructural compounds M(HCOO)2·2H2O (M=Mn,Fe,Co,Ni,Cu,Zn) with matrix-isolated guest ions (Cu2+ in M(HCOO)2·2H2O and M2+ in Cu(HCOO)2·2H2O)

Abstract The infrared spectra of isotopically dilute (matrix-isolated HDO molecules) isostructural compounds M(HCOO) 2 ·2H 2 O (M=Mn,Fe,Co,Ni,Zn,Cu) are presented and discussed in the region of the OD stretching modes. According to the structural data the compounds under study are divided into two groups: in M(HCOO) 2 ·2H 2 O (M=Mn,Ni,Zn) the H 2 O(1) molecules form stronger hydrogen bonds as compared to H 2 O(2); in M(HCOO) 2 ·2H 2 O (M=Fe,Co,Cu) the H 2 O(2) molecules form stronger hydrogen bonds as compared to the H 2 O(1) molecules. The influence of the metal–water interactions (synergetic effect) and the unit-cell volumes (repulsion potential of the lattice) on the hydrogen bond strength within the isostructural series is discussed. The wavenumbers of the uncoupled OD stretching modes of the HDO molecules influenced by guest ions (Cu 2+ ions matrix-isolated in M(HCOO) 2 ·2H 2 O and M 2+ ions matrix-isolated in Cu(HCOO) 2 ·2H 2 O) are presented and commented. For example, the analysis of the spectra reveals that when Cu 2+ ions are included in the structure of M(HCOO) 2 ·2H 2 O the hydrogen bonds of the type M–OH 2 ⋯OCHO–Cu are considerably weaker as compared to those of the same type formed when M 2+ ions are included in the structure of Cu(HCOO) 2 ·2H 2 O if the cations remain unchanged.

Infrared study of νOD modes in isotopically dilute (HDO molecules) Na2Me(XO4)2·2H2O with matrix-isolated X′O42− guest ions (Me=Mn, Co, Ni, Cu, Zn, Cd, and X=S, Se)

Abstract The infrared spectra of related compounds with krohnkite-type chains Na 2 Me(XO 4 ) 2 ·2H 2 O (Me=Mn, Co, Ni, Cu, Zn, Cd, and X=S, Se) containing matrix-isolated X′O 4 2− guest ions and HDO molecules are presented and discussed in the region of the OD stretching modes. The strength of the hydrogen bonds formed in the compounds under study are discussed in terms of the hydrogen bond acceptor strength of the SO 4 2− and SeO 4 2− ions, the respective O w ⋯O bond lengths, the metal–water interactions (synergetic effect), the repulsion potential of the lattice (reduced unit-cell volume), the hydrogen bond acceptor capability of the oxygen atoms. The frequencies of the uncoupled ν OD stretches indicate the formation of stronger hydrogen bonds in the selenate series as compared to the respective compounds of the sulfate one due to the stronger hydrogen bond acceptor capability of the SeO 4 2− ions than that of the SO 4 2− ions. The frequency shifts of ν OD corresponding to the guest ions to higher or lower wavenumbers as compared to the parent compounds (i.e. SO 4 2− guest ions in Na 2 Me(SeO 4 ) 2 ·2H 2 O and SeO 4 2− guest ions in Na 2 Me(SO 4 ) 2 ·2H 2 O, respectively) are due to the translatory and rotatory reorientation of the H 2 O molecules adjacent to the guest ions.

Infrared spectroscopic study of mixed copper-cobalt and copper-nickel formate dihydrates (cation distribution in mixed crystals).

The infrared (IR) spectra of Co(HCOO)2 x 2H2O, Ni(HCOO)2 x 2H2O and Cu2Co(Ni)1-x (HCOO)2 x 2H2O mixed crystals (0 < x < or = 0.5) have been recorded and the internal modes of the formate groups and the water molecules are discussed. The analysis of the spectra of the mixed crystals reveals that when copper ions replace cobalt and nickel ions in Co(HCOO) x 2H2O and Ni(HCOO)2 x 2H2O, the Cu2+ ions are localized at the two available positions. However, the occupancy degree of the Me(1) and Me(2) sites by the different cations needs X-ray diffraction (XRD) studies of the single crystals. The new crystal phase Co0.17Cu0.83(HCOO)2 x 2H2O obtained from the Co(HCOO)2 x 2H2O-Cu(HCOO)2 x 2H2O-H2O system at 50 degrees C crystallizes in the monoclinic system with lattice parameters: a = 12.329(4); b = 7.241(2); c = 8.707(5) A and beta = 103.13(3) degrees (SG probably P2/c). The number of the bands corresponding to the uncoupled OD vibrations and the water librations shows that probably more than two water molecules are expected to exist in the structure. Furthermore, it is assumed that the water molecules bonded to the copper ions form stronger hydrogen bonds (stronger Cu-OH2 interaction) than those bonded to the cobalt ions.

Structural distortion of matrix-isolated SO42− guest ions in selenate crystal hydrates MeSeO4·nH2O (Me=Mg, Mn, Co, Ni, Cu, Zn, n=6, 5, 4)

Abstract We have investigated the vibrational behavior of the S–O stretching modes ν 3 and ν 1 of the matrix-isolated SO 4 2− guest ions isomorphously incorporated in selenate matrices of different crystal structure types: MeSeO 4 ·6H 2 O (Me=Mg, Co, Ni, Zn), MeSeO 4 ·5H 2 O (Me=Mn, Co, Cu, Zn) and MeSeO 4 ·4H 2 O (Me=Co, Ni). The spectra of the SO 4 2− guest ions exhibit less bands corresponding to the S–O stretching modes in all selenate matrices under study than deduced from the site-group analysis. These findings indicate a higher symmetry of the guest ions than the crystallographic one (so-called spectroscopic effective symmetry ). The spectroscopic data may be readily explained with effective symmetry D 2 d of the SO 4 2− guest ions in MeSeO 4 ·5H 2 O, MeSeO 4 ·4H 2 O and in the monoclinic MeSeO 4 ·6H 2 O lattices and with an effective symmetry close to ideal T d in the tetragonal selenate hexahydrate lattices. An adequate measure for the SO 4 2− guest ion distortions is the site group splittings of ν 3 (Δ ν ab ). The values of Δ ν ab are larger, i.e. the distortions increase on going from the hexahydrates to the tetrahydrates. The values of Δ ν ab correlate with the repulsion potential at the lattice sites of the host compounds, i.e. with the reduced cell-volumes.