V. Koleva

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.

Facile synthesis of LiMnPO4 olivines with a plate-like morphology from a dittmarite-type KMnPO4·H2O precursor.

Dittmarite-type compound KMnPO(4)·H(2)O was used as a new precursor for the synthesis of nanostructured LiMnPO(4) phospho-olivines with a plate-like morphology at low temperature (about 200 °C) and a short reaction time (90-180 min). The dehydration of KMnPO(4)·H(2)O was studied by DTA and TG analysis. Structural and morphological characterization of both KMnPO(4)·H(2)O and LiMnPO(4) was performed by powder XRD, SEM and TEM analyses. The formation of nanostructured LiMnPO(4) was examined by electron paramagnetic resonance spectroscopy and TEM. It was found that the reaction between KMnPO(4)·H(2)O with the LiCl-LiNO(3) mixture includes a fast ionic exchange of K(+) with Li(+) in the framework of the dittmarite structure, followed by H(2)O release and the formation of the olivine-type structure. The morphology and texture of the dittmarite-type precursor results in a plate-like morphology of LiMnPO(4) with a preferred orientation along the [100] direction. The plate-like morphology of LiMnPO(4) is stable after annealing at 500 °C. The plates are composed of nanocrystallites, with various sizes in the range 10-20 nm. The EPR signal of LiMnPO(4) is due to the exchange-coupled Mn(2+) ions. It was demonstrated that the EPR line-width correlates with the Scherrer crystallite size.

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) 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.

Competitive lithium and sodium intercalation into sodium manganese phospho-olivine NaMnPO4 covered with carbon black

In this contribution we provide novel data on the reversible lithium and sodium ion intercalation into a sodium-manganese phospho-olivine NaMnPO4, when it is used as a cathode in model lithium-ion cells. The ion-exchange reaction involving the participation of KMnPO4·H2O dittmarite as precursor was chosen for the preparation of NaMnPO4. The NaMnPO4 particles were covered with carbonaceous materials to improve the electrical conductivity and electrolyte wetting. The procedure includes ball-milling of NaMnPO4 with conductive carbon black additives Super C/65, followed by thermal treatment. The mechanically treated samples consist of well crystallized phospho-olivine phase NaMnPO4 free of any anti-site defects and disordered carbon species with graphite like medium-range order. The composite NaMnPO4/C material manifests a reversible capacity between 80–85 mA h g−1 in model lithium cells versus lithium anode. Prior to the electrochemical test, the chemical inertness of NaMnPO4 in the lithium electrolyte is studied by soaking phospho-olivines in the solution of LiPF6 in EC:DMC. The mechanism of the reversible intercalation/deintercalation cycling is investigated using ex situ X-ray powder diffraction, TEM and high-angle annular dark field STEM analysis, infrared spectroscopy and electron paramagnetic resonance spectroscopy (EPR). The study demonstrates, for the first time, that NaMnPO4 is able to intercalate reversibly both Na+ and Li+ ions following the chemical reaction LixNa1−xMnPO4 ↔ Li0.0Na0.5MnPO4 (0.25 ≤ x ≤ 0.45).

Precursor-based methods for low-temperature synthesis of defectless NaMnPO4 with an olivine- and maricite-type structure

We report precursor-based methods for low-temperature synthesis of two structure modifications of NaMnPO4. The maricite phase is thermodynamically more stable, while the olivine phase is of great interest as a positive-electrode material for lithium and sodium ion batteries. The advantage of synthetic procedures is the formation of defectless NaMnPO4 in the temperature range of 200–400 °C. The structure and morphology characterizations of two modifications are performed by powder XRD, SEM and TEM analyses. The oxidation state of the Mn ions in NaMnPO4 is determined by X-ray photoelectron spectroscopy. The local environment of Na in both structure modifications is assessed by 23Na MAS NMR spectroscopy. The synthesis methods are based on the formation of appropriate precursors that are easily transformed to target NaMnPO4. Thermal decomposition of freeze-dried phosphate–formate precursor yields NaMnPO4 with a maricite structure at 400 °C. KMnPO4·H2O with a dittmarite-type structure acts as a structure-template precursor for the preparation of NaMnPO4 with an olivine structure by an ion exchange reaction. Both olivine and maricite NaMnPO4 do not accommodate any anti-site mixing and Na,Mn deficiency. The morphology of NaMnPO4 consists of nano-sized particles (less than 50 nm) that are closely bound together into aggregates, the shape of the aggregates being dependent on the synthesis procedure used.

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.