Photoinduced magnetization in molecular compounds

In this review, recent studies on photoinduced magnetization in molecular compounds are introduced. The magnetic materials presented here range from Prussian blue analogues to purely organic radicals. Various photomagnetic phenomena observed in those materials are briefly described. These are, for example, photoinduced magnetization, photoinduced demagnetization, photoinduced spin cluster, photoinduced magnetic-pole inversion, photoinduced spin flipping, light-induced excited spin state trapping, photoinduced valence tautomerism, etc. It is thought that these can be used for future high-density photo-recording media and optical switches in molecular devices.     

Photoinduced rearrangements in transition metal compounds

In this contribution a range of photoinduced ligand rearrangements observed for the 1st and 2nd row transition metal and organometallic compounds are discussed. The processes discussed include photoinduced ligand exchange, linkage isomerisation and changes occurring within the coordination sphere of the compounds such as cis–trans and fac–mer isomerisations. The relevance of these processes for photocatalytic cycles or their application as synthetic tools is discussed where appropriate.     

Theoretical study of isomerism of compounds of N2 and N2H2 molecules with aluminum clusters Al13 and Al12Ti

Segments of the potential energy surfaces corresponding to successive elementary stages of multistep fragmentation of nitrogen and diimine molecules upon their reaction with the aluminum cluster Al₁₃ and its doped analogue Al₁₂Ti have been calculated by the density functional theory method. The minimum energy pathways of these reactions have been calculated for the stages of physisorption, chemisorption, and N₂ and N₂H₂ fragmentation with different ways of insertion of fragments into the Al₁₃ and Al₁₂Ti cages. Relative energies, structural characteristics, and vibrational frequencies of coordinated and fragment isomers have been calculated, the barriers separating these isomers have been evaluated, and molecular diagrams of the reactions have been constructed. The effect of doping on the relative energies of intermediates and activation barriers has been considered. A conclusion has been drawn that doping with titanium should facilitate the reactions of molecular nitrogen with aluminum clusters. Unusual isomers with a five- and six-coordinate nitrogen atom N* have been localized. The results are compared with the data of analogous previous calculations of the PES of isomers corresponding to stepwise fragmentation of an acetylene molecule in related Al₁₃C₂H₂ and Al₁₂TiC₂H₂ derivatives.     

Photoinduced reactions of aryl-2H-azirines with carbonyl compounds. Preliminary communication

Irradiation of 3-phenyl-( 4 ), 2-methyl-3-phenyl-( 8 ), and 2,3-diphenyl-2H-azirine ( 10 ), in benzene solution in the presence of aldehydes, yields the corresponding aryl-3-oxazolines. Photochemical reaction of 4 and 10 with carbon dioxide leads to the formation of 4-phenyl- ( 15 ) and 2,4-diphenyl-3-oxazolin-5-one ( 16 ), respectively.     

Photoinduced Metallonitrene Formation by N2 Elimination from Azide Diradical Ligands

Transition-metal nitrides/nitrenes are highly promising reagents for catalytic nitrogen-atom-transfer reactivity. They are typically prepared in situ upon optically induced N₂ elimination from azido precursors. A full exploitation of their catalytic potential, however, requires in-depth knowledge of the primary photo-induced processes and the structural/electronic factors mediating the N₂ loss with birth of the terminal metal-nitrogen core. Using femtosecond infrared spectroscopy, we elucidate here the primary molecular-level mechanisms responsible for the formation of a unique platinum(II) nitrene with a triplet ground state from a closed-shell platinum(II) azide precursor. The spectroscopic data in combination with quantum-chemical calculations provide compelling evidence that product formation requires the initial occupation of a singlet excited state with an anionic azide diradical ligand that is bound to a low-spin d⁸-configured Pt^II ion. Subsequent intersystem crossing generates the Pt-bound triplet azide diradical, which smoothly evolves into the triplet nitrene via N₂ loss in a near barrierless adiabatic dissociation. Our data highlight the importance of the productive, N₂-releasing state possessing azide ππ* character as a design principle for accessing efficient N-atom-transfer catalysts.     

Mechanism of formation of short metal-ligand bonds in linear molecules CuCl2 and NiCl2 molecules

The electronic structures of the CuCl₂ and NiCl₂ linear molecules were analyzed in the framework of the extended version of the angular overlap model. The anomalously short metal-ligand bonds in these molecules were shown to be due to the strong sd-mixing of the orbitals of the metal ions.     

Photoinduced gelation by stilbene oxalyl amide compounds

Oxalyl amide derivatives bearing 4-dodecyloxy-stilbene as a cis-trans photoisomerizing unit were synthesized. The trans derivative acted as a versatile gelator of various organic solvents, whereas the corresponding cis derivative showed a poor gelation ability or none at all. In diluted solution (c = 2.0 x10(-5) mol dm(-3), ethanol), the cis isomer was photochemically converted into the trans isomer within 4 min. Depending on the radiation wavelength, the trans isomer was stable or liable to photodecomposition. When exposed to irradiation, a concentrated solution of the cis isomer (c = 2.0 x 10(-2) mol dm(-3), ethanol) turned into a gel. The FT-Raman, FT-IR, and 1H NMR spectra demonstrated that the gelation process occurred because of a rapid cis --> trans photoisomerization followed by a self-assembly of the trans molecules. Apart from the formation of hydrogen bonding between the oxalyl amide parts of the molecules, confirmed by FT-IR spectroscopy, it was assumed that the pi-pi stacking between the trans-stilbene units of the molecule and a lipophilic interaction between long alkyl chains were the interactions responsible for gelation.     

Photoinduced DNA end capping via N3-methyl-5-cyanovinyl-2'-deoxyuridine

A modified oligodeoxynucleotide (ODN) containing N(3)-methyl-5-cyanovinyl-2'-deoxyuridine reacts by photoirradiation at 366 nm with an adenine residue of a complementary template ODN to yield an end-capped ODN in 87% yield.     

Photoinduced reaction of dichloromaleimide with some aromatic compounds

Conclusions The photoreaction of dichloromaleimide with benzene, fluorobenzene, and anisole has been investigated. In the first two cases, the main process comprises the 1,2-addition of two dienophile molecules. The reaction with anisole proceeds exclusively by a scheme comprising substitution to form anisylmaleimides followed by photodimerization.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 401–404, February, 1979.     

Photoinduced reactions of organic compounds with transition metals 22. Polychromate-catalyzed photooxygenation of alkanes and other compounds by O2 OF air in CH2Cl2

Irradiation by light with >520 nm of solutions of cyclohexane, n-hexane, and ethylbenzene in CH₂Cl₂ in air in the presence of the complexes (Bu₄N)₂. Cr₂O₇, (Bu₄N)₂Cr₃O₁₀, or (Bu₄N)₂Cr₄O₁₃ results in formation (after GLC) of the corresponding alcohols and ketones. Under these conditions, styrene epoxide, benzaldehyde, and acetophenone are produced from styrene; alcohols are oxidized to carbonyl compounds; and triphenylphosphine forms triphenylphosphine oxide.For previous communication, see [1]. Preliminary reports have been published [2, 3].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2463–2468, November, 1991.     

Unstable complexes of sandwich compounds and small molecules. 5. Complex formation of carbon dioxide molecules with organometallic compounds of transition elements at low temperatures

Conclusions CO complexes with the cyclopentadienyl and arene complexes of transition metals are formed at 80–90 and 14–16 K on a cold substrate by direct synthesis. The structures of the complexes depend on experimental conditions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2298–2301, October, 1988.     

Electronic structure of chelate compounds of nickel(II) with azo compounds (coordination sites [2N, 2N], [2O, 2N], and [2S, 2N])

Journal of Structural Chemistry -     

Reactions of N2O4 with organic compounds

The previously described method for the one-step synthesis of aryltrinitromethanes from araldoximes may be utilized for the preparation of trinitromethyl derivatives of pyridine and thiophene. In the latter case, in addition to the conversion of the oxime group into the trinitromethyl group, nitration of the thiophene ring also occurs.For part VII, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 5, pp. 590–591, May, 1970.     

Inclusion of quaternary ammonium compounds by calixarenes

In weakly polar solvents, strong association occurs between calixarene anions and tetraalkylammonium cations, with the magnitude of the observed equilibrium constants depending upon the charge on the anion, the solvent, the ring size of the calixarene and the nature of the alkyl group of the cation. Large upfield shifts of the methyl resonances of the [(CH₃)₄N]⁺ cation in solutions of [(CH₃)₄N]₂[p-t-butylcalix[6]arene-2H] indicate cation inclusion in a structure which is possibly identical with that found for the solid salt by X-ray crystallography. This shows one of the cations to be included within a partial cone structure of a hinged 3-up, 3-down conformation of the calixarene. The functionalised tetramethylammonium ions, choline and acetyl choline, are also strongly included by various calixarene anions but attempts to detect significant modification of the reactivity of acetyl choline resulting from inclusion have not been successful.This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes.     

Yield of electronically excited N2 molecules from the dissociative recombination of N2H+ with e-

Quantitative spectroscopic observations of the N2 first positive band system (N2(B 3Pig-A 3Sigmau+))/electron in a recombining N2H+ flowing-afterglow plasma indicate that a substantial fraction of the product N2 molecules are formed in one or more of the low-lying triplet states, B 3Pig, A 3Sigmau+, and W 3Deltau. The total measured N2(B-A) emission intensity from N2(B,v' > or = 1) is equivalent to a yield of (19 +/- 8)%. The effect of rapid collision-induced transitions between states of the triplet manifold is discussed..