Doina Sibiescu

Highly luminescent polystyrene embedded CdSe quantum dots obtained through a modified colloidal synthesis route

The present work describes a modified colloidal synthesis route for the preparation of CdSe nanocrystals, which were further embedded in a polystyrene matrix. Used as a reaction medium, glycerin makes it possible to obtain nanocrystals at lower temperatures in all process stages and an easier separation from the reaction mass. The influence of two different cadmium compounds used as primary cadmium sources over the quality of synthesized CdSe nanocrystals is established. Having a double role, namely in the formation of a cadmium precursor and that of a surface capping agent, three saturated monocarboxylic fatty acids are tested. The synthesis path is refined by evaluating the luminescent properties of CdSe nanocrystals resulting from each test. The obtained CdSe nanocrystals were further embedded in a polystyrene matrix, resulting in a highly luminescent composite. The solution-processed highly luminescent composite might be used as a conversion layer in various optoelectronic devices.

The study of new complex compounds of Ni (II) and Co (II) with N- hydroxy-succinimide and their potential applications as sensors

In this paper, the study of obtaining new coordination compounds of Ni (II) and Co(II) using as ligand, N-hydroxy-succinimide, was presented. Also, the stability constants of these compounds in aqueous medium were determined. The obtaining conditions and the stability of the new compounds were accomplished in aqueous solutions using characteristic methods for coordination compounds: pH-metry, conductometry and UV-VIS absorption spectroscopy. The combination ratios and the stability constants were determined with methods characteristic for studies in solutions. From experimental data resulted that the combination ratio of central metallic atoms with the ligand N-hydroxy-succinimide was: 1:1 and respectively 1:2. In the experiments were used salts of NiCl2·6H2O and CoCl2·6H2O. The optimal domain of pH stability of the studied compounds is limited between 5.74 - 5.86 for Co- N-hydroxy-succinimide (for molar ratio 1:1 and 1:2) and respectively 5.69 - 5.87 for Ni-N-hydroxysuccinimide( for molar ratio 1:1 and 1:2, too). It is important to mention that these compounds were used with very good results in determination of wastewaters from textile, metallurgical, chemical and food industry. Complexion reactions with this ligand are very sensitive for the cations in this paper mentioned. Therefore it is used most often with success in analytical chemistry and also it is posibil to use as sensors. The new complex compounds has electronics transitions at λ = 517 nm for both complexes Co-N-hydroxy-succinimide at molar ratio 1:1 and 1:2 and also at the same λ = 397nm for Ni-N-hydroxysuccinimide at molar ratio 1:1 and 1:2. These complexes compounds was separated and recrystallized from aqueous solution. From the spectrophotometric data it was determined the type and the nature of the electronics transitions by Dq parameters.

NEW COMPLEX COMPOUNDS WITH b-AMINOISOBUTYRIC ACID BIDENTATE LIGAND FOR POTENTIAL APPLICATION IN SUSTAINABLE AGRICULTURE

The synthesis and the study of the complexes obtained in this paper represent the beginning of our research for applied coordinative compounds of this type in agriculture. The analysis and the study of Mn(II) complexes with DL- -Aminoisobutyric acid as ligand were accomplished in aqueous and alcoholic solution and also in solid state.The composition ratios and the stability of the synthesised compounds were analysed with specific methods: conductance, pH measurements, spectrophotometry and thermogravimetry. There were obtained two complexes, at the metal:ligand molar ratio 1:1 and 1:2. In order to determine the structures of the new compounds, the following methods were applied: chemical analysis, IR, UV-VIS and XRD spectroscopy. The [MnLCl]2.2/5H2O and [MnL2].1/2H2O presented a triclinic and respectively, monoclinic crystalline structure. From the thermal decomposition data, the kinetic parameters of the studied compounds were calculated observing that both new complex compounds have a higher thermal stability than the ligand. The experimental data confirmed that ligand DL- -Aminoisobutyric acid presented a bi-dentate behavior towards Mn(II) ions in solution.

New complexes of silver (I) with N-hydroxy-succinimide

Over the last period of time silver was considerably studied due to its lower resistivity. In the field of materials science, silver was used in applications such as: microelectronics components of high – temperature superconductiviting materials, bactericidal coatings and others domains. This study presents the process of obtaining and characterization the new complexes of silver (I) with Nhydroxy- succinimide. In the process of obtaining the new complex compounds in aqous solution, first we have to look at conductometry and UV-Vis absorbtion spectroscopy in order to determine the molar ratio silver : N-hydroxysuccinimide and the stability constants. The obtained solid coordination compounds were characterized by elemental analysis, IR spectroscopy and also was investigated of their thermostability. The X-ray powder diffraction reflects that the complexes compounds of silver (I) with N-hydroxysuccinimide are amorphous. In our further studies we want to determine if the new synthetized compounds will present the same or improuved properties as in the above mentioned silver characteristics.

New coordination compounds of Cr(III) used in leather tanning

Some new coordination compounds of Cr(III) using as ligand N-hydroxy - succinimide, were obtained and studied. The combination ratio, central atom: ligand were 1:1; 1:2 and 1:3. The new complex compounds were studied using UV-Vis spectroscopy, conductance and pH measurements. The studies of obtaining and of stability of the new compounds were accomplished in aqueous solutions using methods characteristic for coordination compounds: conductance and pH measurements. The combination ratios and the stability constants were determined with methods characteristic for studies in solutions.

Studies of obtaining and stability in aqueous medium of new complex compounds of Ti(IV) and Zr(IV) used in ecological leather tanning

In this paper, the study of obtaining new coordination compounds of Ti(IV) and Zr(IV) using as ligand: D,L-β-iso-butyric acid, is presented. Also, the stability of these compounds in aqueous medium is studied. The studies of obtaining and of stability of the new compounds were accomplished in aqueous solutions using methods characteristic for coordination compounds: conductance and pH measurements. The combination ratios and the stability were determined with methods characteristic for studies in solutions. From experimental data resulted that the combination ratio of central metallic atoms with the ligand derived from D,L-β-iso-butyric acid was 1:2. From experimental data resulted that in strong acid and strong basic mediums, the coordination compounds could not be obtained. The optimal stability of the studied compounds is limited between 3-6, pH - values. This fact is in accordance with the conditions of using these compounds in ecological leather tanning. Of great importance is that these compounds were used with very good results in tanning processes of different types of leather. This fact evidenced that the ecological alternative of tanning is better than non-ecological tanning using chrome compounds. The importance of this paper consists in obtaining new coordination compounds that can be used in ecological leather tanning.

Aspects Regarding the Synthesis Mechanism and Kinetics of Some Co-Ordination Polymers

The paper presents some aspects regarding the kinetics and mechanisms of the reactions between the Fe(III) and Cr(III) acetylacetonates with phosphinic acids. The experimental data indicate that the mechanism of the studied reactions is an SN2.