Study of the bands attributable to crystallization water in hydrated metal acetates

Efflorescence on calcareous objects in museums: crystallisation, phase characterisation and crystal structures of calcium acetate formate phases

During the systematic investigation of the ternary system Ca(CH₃COO)₂-Ca(HCOO)₂-H₂O at room temperature, the congruent crystallisation of two solid calcium acetate formates was observed: the hitherto unknown Ca₃(CH₃COO)₄(HCOO)₂·4H₂O and the poorly characterised Ca(CH₃COO)(HCOO)·H₂O. The latter is a frequently observed efflorescence phase found on calcareous objects and it could be also identified as a corrosion phase in a natural history collection of birds' eggs. Elemental and thermal analyses were employed to determine the phase compositions and by Raman and IR spectroscopy the presence of acetate and formate anions in both solids was confirmed. Laboratory X-ray powder diffraction data were used to solve the crystal structures. Ca₃(CH₃COO)₄(HCOO)₂·4H₂O crystallises in a primitive tetragonal unit cell with space group P4₁2₁2 and lattice parameters of a = 6.8655(1) Å and c = 45.5454(6) Å, while Ca(CH₃COO)(HCOO)·H₂O crystallises in a primitive monoclinic unit cell with space group P2₁/c and lattice parameters of a = 9.2729(1) Å, b = 6.8002(1) Å, c = 11.2219(2) Å and β = 121.232(1)°. Calcium carboxylate zig-zag chains [Ca(μ₂-RCOO)⁺]_n (R = CH₃ or H) are the main motif of both crystal structures. In Ca₃(CH₃COO)₄(HCOO)₂·4H₂O these chains are exclusively composed of acetate anions, whereas in Ca(CH₃COO)(HCOO)·H₂O only formate anions are situated in the chains. The remaining places in the 7-8 fold coordination sphere of the calcium cations are filled by water molecules and additional carboxylate anions that interconnect neighbouring chains, which eventually leads to layered motifs in both structures.

On verdigris, part II: synthesis of the 2-1-5 phase, Cu3(CH3COO)4(OH)2·5H2O, by long-term crystallisation from aqueous solution at room temperature

Long-term crystallisation led to the formation of the 2-1-5 verdigris phase (Cu₃(CH₃COO)₄(OH)₂·5H₂O). The crystal structure, as well as magnetic, thermal and spectroscopic properties, was investigated.

On verdigris, part I: synthesis, crystal structure solution and characterisation of the 1-2-0 phase (Cu3(CH3COO)2(OH)4)

Known synthesis approaches for basic copper(ii) acetates, the main components of historic verdrigis pigments were reinvestigated and revealed to be partially irreproducible. A modification of the reaction conditions led to the successful and reproducible synthesis of the 1-2-0 phase (Cu₃(CH₃COO)₂(OH)₄ = 1Cu(CH₃COO)₂·2Cu(OH)₂·0H₂O). The phase composition was derived from elemental and thermal analysis and confirmed by the crystal structure solution using synchrotron X-ray powder diffraction (XRPD) data. The 1-2-0 phase crystallises in space group Pbca with lattice parameters of a = 20.9742(1) Å, b = 7.2076(1) Å, and c = 13.1220(1) Å. The crystal structure consists of Cu₂(CH₃-COO)₂(OH)_4/3(OH)_2/2^1/3- dimers, which are interconnected by corner sharing Cu(OH)_2/3(OH)_2/2^1/3+ squares forming layers perpendicular to the a-axis. The deep blue color of the solid originates from a reflectance maximum at 472 nm and from an absorbance maximum at 676 nm that is comparable with other historic blue pigments like azurite or Egyptian blue. IR- and Raman-spectroscopic properties of the solid were investigated as well, which demonstrated that the obtained product is identical with a previously synthesised verdigris phase that was obtained by applying historical procedures. Therefore, our reference data for the title compound will help to improve the understanding of the multiphase mixtures occurring in historic verdigris samples. The magnetic properties of the 1-2-0 phase were also investigated. At low temperatures the magnetic susceptibility is well described by a spin-1/2 Heisenberg chain with uniform antiferromagnetic nearest-neighbour spin exchange coupling of only one of three Cu magnetic moments. Due to the very strong antiferromagnetic coupling of the Cu₂(CH₃-COO)₂(OH)_4/3(OH)_2/2^1/3- dimers their contribution to magnetism becomes relevant above ∼140 K, which results in the presence of two distinct temperature regions where Curie-Weiss behaviour of the magnetic susceptibility with different Curie constants and Weiss temperatures is found.

Converting Layered Zinc Acetate Nanobelts to One-dimensional Structured ZnO Nanoparticle Aggregates and their Photocatalytic Activity

We were successful in synthesizing periodic layered zinc acetate nanobelts through a hydrothermal solution process. One-dimensional structured ZnO nanoparticle aggregate was obtained by simple thermal annealing of the above-mentioned layered ZnO acetate nanobelts at 300 °C. The morphology, microstructure, and composition of the synthesized ZnO and its precursors were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and infrared spectroscopy, respectively. Low angle X-ray diffraction spectra reveal that as-synthesized zinc acetate has a layered structure with two interlayer d-spacings (one is 1.32 nm and the other is 1.91 nm). SEM and TEM indicate that nanobelt precursors were 100–200 nm in width and possesses length up to 30 μm. Calcination of precursor in air results in the formation of one-dimensional structured ZnO nanoparticle aggregates. In addition, the as-prepared ZnO nanoparticle aggregates exhibit high photocatalytic activity for the photocatalytic degradation of methyl orange (MO).

Metal isotope and density functional study of the tetracarboxylatodicopper(II) core vibrations

Vibrational spectra of tetrakis(acetato)diaquadicopper(II) complex have been deeply examined in order to provide a detailed description of dynamics of [Cu(2)O(8)C(4)] core being a typical structural unit of most copper(II) carboxylates. Low frequency bands related to significant motions of metal atoms were detected by metal isotope substitution. Observed spectra and isotope shifts were reproduced in DFT calculations. For clear presentation of computed normal vibrations, a D(4h) symmetry approximation was successfully applied. Basing on observed isotope shifts and calculation results, all skeletal vibrations have been analyzed including normal mode with the largest Cu...Cu stretching amplitude assigned to Raman band at 178 cm(-1).

Raman Spectroscopic Studies on Single Supersaturated Droplets of Sodium and Magnesium Acetate

Raman spectroscopy was used to study structural changes, in particular, the formation of contact-ion pairs in supersaturated aqueous NaCH(3)COO and Mg(CH(3)COO)(2) droplets at ambient temperatures. The single droplets levitated in an electrodynamic balance (EDB), lost water, and became supersaturated when the relative humidity (RH) decreased. For NaCH(3)COO droplet the water-to-solute molar ratio (WSR) was 3.87 without solidification when water molecules were not enough to fill in the first hydration layer of Na(+), in favor of the formation of contact-ion pairs. However, the symmetric stretching vibration band (nu(3) mode) of free -COO(-) constantly appeared at 1416 cm(-1), and no spectroscopic information related to monodentate, bidentate, or bridge bidentate contact-ion pairs was observed due to the weak interactions between the Na(+) and acetate ion. On the other hand, the band of methyl deformation blue shifted from 1352 to 1370 cm(-1) (at RH = 34.2%, WSR = 2.43), corresponding to the solidification process of a novel metastable phase in the highly supersaturated solutions. With further decreasing RH, a small amount of supersaturated solution still existed and was proposed to be hermetically covered by the metastable phase of the particle. In contrast, the interaction between Mg(2+) and acetate ion is much stronger. When WSR decreased from 21.67 to 2.58 for the Mg(CH(3)COO)(2) droplet, the band of C-C-symmetric stretching (nu(4) mode) had a blue shift from 936 to 947 cm(-1). The intensity of the two new shoulders (approximately 1456 and approximately 1443 cm(-1)) of the nu(3) band of free -COO(-) at 1420 cm(-1) increased with the decrease of WSR. These changes were attributed to the formation of contact-ion pairs with bidentate structures. In particular, the small frequency difference between the shoulder at approximately 1443 cm(-1) and the nu(3) band of the free -COO(-) group (approximately 1420 cm(-1)) was proposed to be related to the formation of a chain structure based on the contact-ion pairs of bridge bidentate. The continuous formation of various contact-ion pairs started at higher WSR value (WSR = 15.5) greatly reduced the hygroscopic properties of Mg(CH(3)COO)(2) droplet, so that the WSR of Mg(CH(3)COO)(2) droplets was even lower than that of NaCH(3)COO in the RH range of 40-60%.