Gayane A. Kirakosyan

Speciation of heptavalent technetium in sulfuric acid: structural and spectroscopic studies

The speciation of Tc(vii) was studied in 12 M H(2)SO(4) by NMR, UV-visible and XAFS spectroscopy. Experimental results and density functional calculations show the formation of TcO(3)(OH)(H(2)O)(2).

Macrocyclic receptor for pertechnetate and perrhenate anions

The design and synthesis of a neutral macrocyclic host that is capable of perrhenate and pertechnetate recognition is described. The anion affinities and underlying coordination modes were estimated by several experimental and theoretical methods including a new technique--reverse (99)Tc NMR titration.

A Molecular Chameleon: Reversible pH- and Cation-Induced Control of the Optical Properties of Phthalocyanine-Based Complexes in the Visible and Near-Infrared Spectral Ranges

A series of novel nonperipherally substituted tetra-15-crown-5-dibutoxyoxanthrenocyanines (H2, Mg, Zn), acting as chameleons with the unique properties of switchable absorption and emission in the near-infrared (NIR) spectral range have been synthesized and characterized by X-ray diffraction. The attachment of 15-crown-5-α-dibutoxyoxanthreno moieties to phthalocyanine is responsible for the high solubility of the resulting molecules and the red shift of the Q band to the NIR region and offers a unique possibility for postsynthetic modification of the optical properties of the molecules. Both aggregation of phthalocyanine and its participation in an acid-base equilibrium strongly alter their optical properties. For example, the absorption of complexes can be reversibly tuned from 686 up to 1028 nm because of the cation-induced formation of supramolecular dimers or subsequent protonation of meso-N atoms orf macrocycle, in contrast to peripherally substituted tetra-15-crown-5-phthalocyanines without oxanthrene moieties. The reversibility of these processes can be controlled by the addition of [2.2.2]cryptand or amines. All investigated compounds exhibit fluorescence with moderate quantum yield, which can also be switched between the ON and OFF states by the action of similar agents.

Oxygen isotope effect on NMR parameters of pertechnetate anion TcO 4

The effects of oxygen isotope substitution 16O ↔ 17O ↔ 18O in the coordination sphere of the pertechnetate anion (TcO4−) on the NMR 99Tc chemical shifts and 99Tc-17O and 17O-99Tc spin coupling constants have been studied by 17O and 99Tc NMR. The isotope shifts 16/17Δ and 16/18Δ in 99Tc NMR and the spin coupling constants of the Tc16O217O2−, Tc 16O318O−, Tc 16O317O−, Tc 16O217O18O−, and Tc16O218O2− isotopomers have been measured. For the Tc 16O318O− and Tc 16O317O− anions in an ammonium pertechnetate solution, the temperature dependences of the isotope shift in the temperature range 278–333 K are described by linear relationships 16/18Δ = −0.616 + 6.45 × 10−4T (ppm) and 16/17Δ = −0.302 + 2.67 × 10−4T (ppm), respectively. For the Tc16O317O− anion in a sodium pertechnetate solution, the magnitude of the 1Δ(16/17O) isotope shift nonlinearly decreases with increasing temperature. The nonlinear temperature dependence of the J(99Tc-17O) spin coupling constant and the extreme point on the curve of the 1Δ(16/18O) isotope shift versus temperature for the isotopomers in an NaTcO4 solution are presumably related to equilibrium between contact and water-separated ion pairs.

Cation-Induced Dimerization of Crown-Substituted Phthalocyanines by Complexation with Rubidium Nicotinate As Revealed by X-ray Structural Data

The supramolecular dimeric complex [(μ-oxo)bis(tetra-15-crown-5-phthalocyaninato)(nicotinato)aluminum(III)]tetra(rubidium) bis(nicotinate) was prepared by addition of an excess of a methanol solution of rubidium nicotinate to a chloroform solution of the aluminum crown-phthalocyaninate, [(HO)Al(15C5)4Pc]. A single-crystal X-ray diffraction study of {[Rb4(NicAl(15C5)4Pc)2(μ-O)]2+(Nic-)2}·2.36HNic·11H2O demonstrated that two molecules of the aluminum crown-phthalocyaninate nicotinate are connected through an Al-O-Al bridge supported by sandwiching of crown ether moieties by Rb+ cations.

16O/18O oxygen isotope exchange kinetics in MnO4− as probed by 55Mn NMR

The effect of the 16O ↔ 18O substitution in the coordination sphere of permanganate anion MnO4− on the chemical shift of 55Mn nuclei have been studied by 17O and 55Mn NMR. Time constants τn,k of oxygen exchange in the water–permanganate anion system have been estimated. In nearly neutral solutions (pH ≈ 6.8–7.2), the oxygen exchange time is on the order of tens of hours. Bubbling gaseous HCl through this solution for a few seconds leads to the equilibrium distribution of oxygen isotopes in the manganese coordination sphere. The observed temperature dependences of isotope-induced 55Mn NMR shifts in Mn16 O44-n18On– (n = 0–4) have been treated as a result of rovibrational averaging of Mn–O bond lengths. The change in the Mn—O bond length in caused by the 16O → 18O isotope substitution is on the order of 10–4 Å.

CCDC 1566600: Experimental Crystal Structure Determination

Related Article: Lyudmila A. Lapkina, Vladimir E. Larchenko, Gayane A. Kirakosyan, Aslan Yu. Tsivadze, Sergey I. Troyanov, Yulia G. Gorbunova|2017|Inorg.Chem.|||doi:10.1021/acs.inorgchem.7b01983

Gallium(III) and Indium(III) Complexes with meso-Monophosphorylated Porphyrins: Synthesis and Structure. A First Example of Dimers Formed by the Self-Assembly of meso-Porphyrinylphosphonic Acid Monoester

The synthesis and structural characterization, both in solution by means of 1H and 31P NMR and UV-vis spectroscopies and in the solid state by X-ray diffraction on single crystal, of a series of gallium(III) and indium(III) meso-mono(diethoxyphosphoryl)porphyrins bearing different peripheral substituents as well as the corresponding monoesters and phosphonic acids are reported. This work describes the first example of the X-ray structure of a self-assembled dimer formed via strong binding between the oxygen atom of the phosphonate substituent and the gallium(III) cations of adjacent porphyrin molecules [Ga-O = 1.9708(13) Å].