| 1. |
- Martinez, Francisco, et al.
(författare)
-
Short lead(II) soaps: from weakly fluorescent crystals to strongly phosphorescent and structurally varied vitreous phases. A thermal, structural and spectroscopic study
- 2014
-
Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7526. ; 2:44, s. 9489-9496
-
Tidskriftsartikel (refereegranskat)abstract
- Short lead(II) alkanoates, from propionate to heptanoate, show a very intricate and reversible thermal behaviour, presenting crystalline phases and three different glass states (regular or amorphous, liquid crystal and rotator glasses) with different degrees of ordering depending on the alkyl chain length. A thorough thermal study was carried out in order to study the different phases and to analyze the thermodynamic parameters. The crystal structures of the compounds were solved by X-ray diffraction, showing similar arrangements of the 2D molecular stacking. PDF analyses of the local order in the glass structures showed shorter first neighbour lead-lead interatomic distances than in the crystalline structures. This allows establishment of a direct relationship between the structure and optical properties. Luminescence properties are, in fact, impressively enhanced in the glass states, passing from weak fluorescence at 77 K in the crystal phase to strong phosphorescence in the frozen glasses, which persists at room temperature. The high variability and the structure-property relationship described here pave the way for the design of materials with varied luminescence properties based on fine-tuning of their local structure.
|
|
| 2. |
- Martinez, Francisco, et al.
(författare)
-
Unraveling the Decomposition Process of Lead(II) Acetate : Anhydrous Polymorphs, Hydrates, and Byproducts and Room Temperature Phosphorescence
- 2016
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 55:17, s. 8576-8586
-
Tidskriftsartikel (refereegranskat)abstract
- Lead(II) acetate [Pb(Ac)2, where Ac = acetate group (CH3-COO-)2] is a very common salt with many and varied uses throughout history. However, only lead(II) acetate trihydrate [Pb(Ac)2·3H2O] has been characterized to date. In this paper, two enantiotropic polymorphs of the anhydrous salt, a novel hydrate [lead(II) acetate hemihydrate: Pb(Ac)2·1/2H2O], and two decomposition products [corresponding to two different basic lead(II) acetates: Pb4O(Ac)6 and Pb2O(Ac)2] are reported, with their structures being solved for the first time. The compounds present a variety of molecular arrangements, being 2D or 1D coordination polymers. A thorough thermal analysis, by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), was also carried out to study the behavior and thermal data of the salt and its decomposition process, in inert and oxygenated atmospheres, identifying the phases and byproducts that appear. The complex thermal behavior of lead(II) acetate is now solved, finding the existence of another hydrate, two anhydrous enantiotropic polymorphs, and some byproducts. Moreover, some of them are phosphorescent at room temperature. The compounds were studied by TGA, DSC, X-ray diffraction, and UV-vis spectroscopy.
|
|
| 3. |
- Ramos Riesco, Miguel, et al.
(författare)
-
New Advances in the One-Dimensional Coordination Polymer Copper(II) Alkanoates Series: Monotropic Polymorphism and Mesomorphism
- 2015
-
Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 15:4, s. 2005-2016
-
Tidskriftsartikel (refereegranskat)abstract
- The polymorphism in the copper(II) alkanoates, recently discovered for one member, has been thoroughly studied for the whole series, from 3 to 16 C atoms. Three polymorphic phases have been found, all of them sharing the same molecular unit, the paddle-wheel, which grows forming a 1D coordination polymer or catena. The three polymorphs are defined by a different packing of these catenae and a specific arrangement of the alkyl chains. Ten new crystal structures of those compounds have been solved by high resolution powder diffraction and presented in this paper. The polymorphism in this series has been found to be monotropic and is responsible for the complex thermal behavior observed. The most characteristic feature, the endothermic−exothermic effect, has been explained for the first time in these compounds by a combination of data from differential scanning calorimetry (in normal and modulated modes), powder X-ray diffraction and Fourier transform infrared spectroscopy. These techniques, together with small-angle X-ray scattering and optical microscopy, were used to analyze the hexagonal columnar discotic liquid crystal phase of copper(II) alkanoates. Thus, new information has been found in the packing and stacking of the discs formed by the paddle-wheel units, also maintained in the mesophase.
|
|
