Tigran Kurtikyan - Academia.edu (original) (raw)
Uploads
Papers by Tigran Kurtikyan
Inorganica Chimica Acta
Abstract The adducts of Co(II)(TPP) and Fe(II)TPP (TPP is meso-tetraphenyl-porphyrinato dianion) ... more Abstract The adducts of Co(II)(TPP) and Fe(II)TPP (TPP is meso-tetraphenyl-porphyrinato dianion) with carbon monoxide in Ar matrix at 10 K have been studied by FTIR spectroscopy using CO, C18O and their equimolar mixture. It is shown that both metals may form mono-carbonyl adducts with CO, however formation of bis-carbonyl adduct was confirmed only for iron porphyrin. These results refute an earlier assumption regarding existence of Co(TPP)(CO)2 in Ar matrix.
Inorganic Chemistry, 2013
The oxy-cobolglobin models of the general formula (Py)Co(Por)(O2) (Por = meso-tetraphenyl- and me... more The oxy-cobolglobin models of the general formula (Py)Co(Por)(O2) (Por = meso-tetraphenyl- and meso-tetra-p-tolylporphyrinato dianions) were constructed by sequential low-temperature interaction of Py and dioxygen with microporous layers of Co-porphyrins. At cryogenic temperatures small increments of NO were introduced into the cryostat and the following reactions were monitored by the FTIR and UV-visible spectroscopy during slow warming. Similar to the recently studied (NH3)Co(Por)(O2) system (Kurtikyan et al. J. Am. Chem. Soc., 2012, 134, 13671-13680), this interaction leads to the nitric oxide dioxygenation reaction with the formation of thermally unstable nitrato complexes (Py)Co(Por)(η(1)-ONO2). The reaction proceeds through the formation of the six-coordinate peroxynitrite adducts (Py)Co(Por)(OONO), as was demonstrated by FTIR measurements with the use of isotopically labeled (18)O2, (15)NO, N(18)O, and (15)N(18)O species and DFT calculations. In contrast to the ammonia system, however, the binding of dioxygen in (Py)Co(Por)(O2) is weaker and the second reaction pathway takes place due to autoxidation of NO by rebound O2 that in NO excess gives N2O3 and N2O4 species adsorbed in the layer. This leads eventually to partial formation of (Py)Co(Por)(NO) and (Py)Co(Por)(NO2) as a result of NO and NO2 reactions with five-coordinate Co(Por)(Py) complexes that are present in the layer after the O2 has been released. The former is thermally unstable and at room temperature passes to the five-coordinate nitrosyl complex, while the latter is a stable compound. In these experiments at 210 K, the layer consists mostly of six-coordinate nitrato complexes and some minor quantities of six-coordinate nitro and nitrosyl species. Their relative quantities depend on the experimental conditions, and the yield of nitrato species is proportional to the relative quantity of peroxynitrite intermediate. Using differently labeled nitrogen oxide isotopomers in different stages of the process the formation of the caged radical pair after homolytic disruption of the O-O bond in peroxynitrite moiety is clearly shown. The composition of the layers upon farther warming to room temperature depends on the experimental conditions. In vacuo the six-coordinate nitrato complexes decompose to give nitrate anion and oxidized cationic complex Co(III)(Por)(Py)2. In the presence of NO excess, however, the nitro-pyridine complexes (Py)Co(Por)(NO2) are predominantly formed formally indicating the oxo-transfer reactivity of (Py)Co(Por)(η(1)-ONO2) with regard to NO. Using differently labeled nitrogen in nitric oxide and coordinated nitrate a plausible mechanism of this reaction is suggested based on the isotope distribution in the nitro complexes formed.
Inorganic Chemistry, 2003
Interaction of a low-pressure NO 2 with sublimed layers of (meso-tetraphenylporphyrinato)cobalt(I... more Interaction of a low-pressure NO 2 with sublimed layers of (meso-tetraphenylporphyrinato)cobalt(II) (Co(TPP)) leads to formation of 5-coordinate nitro complex Co(III)(TPP)(NO 2). Upon exposure of these layers to pyridine vapors, the fast reaction with formation of 6-coordinate nitro-pyridine porphyrins (Py)Co(III)(TPP)(NO 2) occurs. By means of IR spectroscopy and use of nitrogen oxide isotopomers, it is shown that an oxo-transfer reaction occurs from 5-coordinate species to free nitric oxide (NO) while the 6-coordinate complex is rather inert. It is also demonstrated that the stepwise addition of low-pressure NO 2 to nitrosyl complex Co(TPP)(NO) leads to formation of the nitro complex most likely by an exchange reaction.
European Journal of Inorganic Chemistry, 2003
The low-temperature interaction of NO(15NO ) with sublimed layers of meso-mono-4-pyridyl-tri-phen... more The low-temperature interaction of NO(15NO ) with sublimed layers of meso-mono-4-pyridyl-tri-phenyl- and meso-mono-3-pyridyl-tri-phenyl-porphyrinatocobalt(II) ( CoM4PyTPP (I) and CoM3PyTPP (II), respectively) has been investigated by means of FTIR and UV-visible spectroscopy. In addition to the stable five-coordinate nitrosyl complexes that are similar to the closely-related meso-tetraphenylporphyrinatocobalt(II)-nitrosyl Co(TPP)(NO) complex, a new type of complex with coordinated NO (15 NO ) has been found for the layers that were maintained at room temperature overnight before addition of nitric oxide at low temperature. The ν{ NO (15 NO )} in this species are more than 20 cm−1 lower than in five-coordinate compounds. These adducts are assigned to six-coordinate nitrosyl complexes, in which the fifth coordination site is occupied by the pyridyl group of the adjacent I (II) molecules. Warming the layers containing six-coordinate nitrosyl complexes of I almost completely transforms them to stable five-coordinate nitrosyl species indicating oligomers' disruption rather than loss of nitric oxide. In the case of II, however, a noticeable fraction of the six-coordinate species is left upon warming. Introducing new portions of NO to these layers at low temperature leads to formation of additional quantities of the six-coordinate species. Hence, part of six-coordinate complexes in II decomposed upon warming by releasing NO instead of by breaking Co -pyridyl bonds, therefore leaving free the sixth coordination sites in these layers. This result suggests a good possibility for creating solid state NO storage devices in which nitrogen monoxide can be kept and easily released by warming of the system.
Inorganic …, 2005
Derivatives of (nitro)cobalt picket fence porphyrin with oxygen-donating ligands have been prepar... more Derivatives of (nitro)cobalt picket fence porphyrin with oxygen-donating ligands have been prepared in solution and in the solid state. Crystal structures of two of these derivatives, (H 2 O)CoTpivPP(NO 2 ) and (CH 3 OH)CoTpivPP(NO 2 ), have been determined. The ethanol ...
Inorganica Chimica Acta
Abstract The adducts of Co(II)(TPP) and Fe(II)TPP (TPP is meso-tetraphenyl-porphyrinato dianion) ... more Abstract The adducts of Co(II)(TPP) and Fe(II)TPP (TPP is meso-tetraphenyl-porphyrinato dianion) with carbon monoxide in Ar matrix at 10 K have been studied by FTIR spectroscopy using CO, C18O and their equimolar mixture. It is shown that both metals may form mono-carbonyl adducts with CO, however formation of bis-carbonyl adduct was confirmed only for iron porphyrin. These results refute an earlier assumption regarding existence of Co(TPP)(CO)2 in Ar matrix.
Inorganic Chemistry, 2013
The oxy-cobolglobin models of the general formula (Py)Co(Por)(O2) (Por = meso-tetraphenyl- and me... more The oxy-cobolglobin models of the general formula (Py)Co(Por)(O2) (Por = meso-tetraphenyl- and meso-tetra-p-tolylporphyrinato dianions) were constructed by sequential low-temperature interaction of Py and dioxygen with microporous layers of Co-porphyrins. At cryogenic temperatures small increments of NO were introduced into the cryostat and the following reactions were monitored by the FTIR and UV-visible spectroscopy during slow warming. Similar to the recently studied (NH3)Co(Por)(O2) system (Kurtikyan et al. J. Am. Chem. Soc., 2012, 134, 13671-13680), this interaction leads to the nitric oxide dioxygenation reaction with the formation of thermally unstable nitrato complexes (Py)Co(Por)(η(1)-ONO2). The reaction proceeds through the formation of the six-coordinate peroxynitrite adducts (Py)Co(Por)(OONO), as was demonstrated by FTIR measurements with the use of isotopically labeled (18)O2, (15)NO, N(18)O, and (15)N(18)O species and DFT calculations. In contrast to the ammonia system, however, the binding of dioxygen in (Py)Co(Por)(O2) is weaker and the second reaction pathway takes place due to autoxidation of NO by rebound O2 that in NO excess gives N2O3 and N2O4 species adsorbed in the layer. This leads eventually to partial formation of (Py)Co(Por)(NO) and (Py)Co(Por)(NO2) as a result of NO and NO2 reactions with five-coordinate Co(Por)(Py) complexes that are present in the layer after the O2 has been released. The former is thermally unstable and at room temperature passes to the five-coordinate nitrosyl complex, while the latter is a stable compound. In these experiments at 210 K, the layer consists mostly of six-coordinate nitrato complexes and some minor quantities of six-coordinate nitro and nitrosyl species. Their relative quantities depend on the experimental conditions, and the yield of nitrato species is proportional to the relative quantity of peroxynitrite intermediate. Using differently labeled nitrogen oxide isotopomers in different stages of the process the formation of the caged radical pair after homolytic disruption of the O-O bond in peroxynitrite moiety is clearly shown. The composition of the layers upon farther warming to room temperature depends on the experimental conditions. In vacuo the six-coordinate nitrato complexes decompose to give nitrate anion and oxidized cationic complex Co(III)(Por)(Py)2. In the presence of NO excess, however, the nitro-pyridine complexes (Py)Co(Por)(NO2) are predominantly formed formally indicating the oxo-transfer reactivity of (Py)Co(Por)(η(1)-ONO2) with regard to NO. Using differently labeled nitrogen in nitric oxide and coordinated nitrate a plausible mechanism of this reaction is suggested based on the isotope distribution in the nitro complexes formed.
Inorganic Chemistry, 2003
Interaction of a low-pressure NO 2 with sublimed layers of (meso-tetraphenylporphyrinato)cobalt(I... more Interaction of a low-pressure NO 2 with sublimed layers of (meso-tetraphenylporphyrinato)cobalt(II) (Co(TPP)) leads to formation of 5-coordinate nitro complex Co(III)(TPP)(NO 2). Upon exposure of these layers to pyridine vapors, the fast reaction with formation of 6-coordinate nitro-pyridine porphyrins (Py)Co(III)(TPP)(NO 2) occurs. By means of IR spectroscopy and use of nitrogen oxide isotopomers, it is shown that an oxo-transfer reaction occurs from 5-coordinate species to free nitric oxide (NO) while the 6-coordinate complex is rather inert. It is also demonstrated that the stepwise addition of low-pressure NO 2 to nitrosyl complex Co(TPP)(NO) leads to formation of the nitro complex most likely by an exchange reaction.
European Journal of Inorganic Chemistry, 2003
The low-temperature interaction of NO(15NO ) with sublimed layers of meso-mono-4-pyridyl-tri-phen... more The low-temperature interaction of NO(15NO ) with sublimed layers of meso-mono-4-pyridyl-tri-phenyl- and meso-mono-3-pyridyl-tri-phenyl-porphyrinatocobalt(II) ( CoM4PyTPP (I) and CoM3PyTPP (II), respectively) has been investigated by means of FTIR and UV-visible spectroscopy. In addition to the stable five-coordinate nitrosyl complexes that are similar to the closely-related meso-tetraphenylporphyrinatocobalt(II)-nitrosyl Co(TPP)(NO) complex, a new type of complex with coordinated NO (15 NO ) has been found for the layers that were maintained at room temperature overnight before addition of nitric oxide at low temperature. The ν{ NO (15 NO )} in this species are more than 20 cm−1 lower than in five-coordinate compounds. These adducts are assigned to six-coordinate nitrosyl complexes, in which the fifth coordination site is occupied by the pyridyl group of the adjacent I (II) molecules. Warming the layers containing six-coordinate nitrosyl complexes of I almost completely transforms them to stable five-coordinate nitrosyl species indicating oligomers' disruption rather than loss of nitric oxide. In the case of II, however, a noticeable fraction of the six-coordinate species is left upon warming. Introducing new portions of NO to these layers at low temperature leads to formation of additional quantities of the six-coordinate species. Hence, part of six-coordinate complexes in II decomposed upon warming by releasing NO instead of by breaking Co -pyridyl bonds, therefore leaving free the sixth coordination sites in these layers. This result suggests a good possibility for creating solid state NO storage devices in which nitrogen monoxide can be kept and easily released by warming of the system.
Inorganic …, 2005
Derivatives of (nitro)cobalt picket fence porphyrin with oxygen-donating ligands have been prepar... more Derivatives of (nitro)cobalt picket fence porphyrin with oxygen-donating ligands have been prepared in solution and in the solid state. Crystal structures of two of these derivatives, (H 2 O)CoTpivPP(NO 2 ) and (CH 3 OH)CoTpivPP(NO 2 ), have been determined. The ethanol ...