Crystals of the CuII complex with nitronyl nitroxide and imino nitroxide exhibiting mechanical activity

As part of continuing studies of multispin compounds capable of exhibiting chemomechanical activity, a series of heterospin solids of the composition [Cu(hfac)₂L _x L′_2?x ], [Cu(hfac)₂L′], [Cu₂(Piv)₄L′₂]·0.5C₆H₁₄, and [Cu₂(hfac)₂(Piv)₂L′2], where hfac is the hexafluoroacetylacetonate anion, L is 4,4,5,5-tetramethyl-2-(1-methyl-1H-imidazol-5-yl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl, L′ is the imino nitroxide analog of L, viz., 4,4,5,5-tetramethyl-2-(1-methyl-1H-imidazol-5-yl)-4,5-dihydro-1H-imidazole-1-oxyl, and Piv is the 2,2-dimethylpropionate anion, were synthesized and characterized. The packing of the synthesized crystals of the solid solutions [Cu(hfac)₂L _x L′_2-x ], where L predominates, is similar to that for [Cu(hfac)₂L₂], and these crystals are able to undergo chemomechanical motion. On the contrary, the crystals of [Cu(hfac)₂L _x L′_2?x ], where L′ predominates, have structural parameters similar to those of [Cu(hfac)₂L′₂] and do not exhibit thermally activated or photoactivated chemomechanical activity.     

Structures of cerium manganese pivalates

The Ce,Mn mixed-metal polynuclear compounds [Ce ₃Mn₆(O)₅(OH)₃Piv₁₂Cl₂(THF)₃]·2THF, [Ce₃Mn₈(O)₈Piv₁₆Cl₂(HPiv)₂]·C₇H₁₆, [Ce₁₀Mn₄(O)₆(OH)₁₂Piv₁₆Cl₂(THF)₂]·2THF·2H₂O, [CeMn₁₁Cl₃(O)₈Piv₁₅(H₂O)]·CH₂Cl₂, and [CeMn₈(O)₈Piv₁₂(HPiv)₂(THF)₂] were prepared and structurally characterized. The possibility of synthesizing p,d,f-heterospin complexes by replacing coordinated THF molecules by nitroxide molecules was exemplified by the reaction of [Ce₃Mn₆(O)₅(OH)₃Piv₁₂Cl₂(THF)₃]·2THF with nitronyl nitroxides (NIT-R is 2-R-4,4,5,5-tetramethyl-24midazoline-l-oxyl 3-oxide; R is Me or 4-Py). The X-ray diffraction study of these complexes showed that [Ce₃Mn₆(O)₅(OH)₃Piv₁₂Cl₂(HPiv)(NIT-Me)₂] and [CeMn₈(O)₈Piv₁₂(NIT4-Py) ₄] · 2C₆H₁₄ have a molecular structure and [Ce₃Mn₆(O)₅(OH)₃-Piv₁₂Cl₂(NIT-Me)(H₂O)] is an infinite chain.     

The structure and magnetic properties of pyrazolyl-substituted benzimidazole-1-oxyl

The structure and magnetic properties of the benzimidazole-based nitronyl nitroxide radical containing pyrazole as a substituent in its side chain were studied.     

2- and 3-phenylsulfonylindoles – synthetic equivalents of unsubstituted indole in N-alkylation reactions

The N-alkylation of 2- and 3-phenylsulfonylindoles under various conditions and the subsequent removal of the activating phenylsulfonyl group by reductive desulfonylation using Raney nickel leads to N-alkylindoles in high yield. 2-Phenylsulfonylindole readily undergoes the Mitsunobu reaction, while isomeric 3-phenylsulfonylindole is relatively inert under these conditions.     

Influence of deviation from stoichiometry on the plasticity and mechanism of fracture of the boron-alloyed intermetallic compound Ni3Al obtained by self-propagating high-temperature synthesis

We have studied the effect that deviation of the composition of an ally from stoichiometry has on the plasticity , strength _B, and the fracture mechanism of the intermetallic compound Ni₃Al obtained by self-propagating high-temperature synthesis. The variation of the tensile strength, plasticity, type of fracture, and the cohesive strength _coh of grains have been show to be correlated. The cohesive strength increases with the Al content in the alloy, most rapidly up to 24.0 at. % Al.V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk State University. Institute of Strength Physics and Materials Science, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 104–110, April, 1994.     

Structural characterization of isomeric 2,3,5‐substituted tetrahydropyrrolo[3,4‐d]isoxazole‐4,6‐diones prepared by cycloaddition of N‐methyl‐C‐arylnitrones to N‐phenyl‐ or N‐methylmaleimide

1,3‐Dipolar cycloaddition reactions of N‐methyl‐C‐arylnitrones with N‐phenyl‐ or N‐methylmaleimide were studied. The reaction of p‐dimethylamino‐, 4‐benzyloxy‐3‐methoxy‐, p‐nitro‐ and p‐chloro‐substituted phenylnitrones with N‐phenylmaleimide gave cis and trans cycloadducts but that of the corresponding phenylnitrones with N‐methylmaleimides only the cis adducts in the case of p‐dimethylamino and 4‐benzyloxy‐3‐methoxy substitution. All cis adducts attain a biased conformation whereas the trans forms are shown (by ¹H NMR at 233 K and ¹³C NMR at 208 K) to be mixtures of two invertomers, namely o‐(N‐lone pair antiperiplanar to 3H; minor) and i‐conformations (3H‐C‐C‐3aH dihedral angle close to 90°; major). PM3 and DFT calculations at the B3LYP/6–31G(d) level of theory prove qualitatively that these two conformers of the trans adduct are of comparable stability and represent energy minima.     

Mass spectrometric identification of ring-chain tautomers of 4-cyano-3-pyrazolidones in the gas phase

Analysis of the electron impact mass spectra of a series of 4-cyano-3-pyrazolidones, which manifest ring-chain tautomerism in polar solvents, showed that these compounds also exist in the gas phase as a mixture of tautomers, which undergo characteristic fragmentation. The quantitative tautomer ratio in this series is a function of electronic and steric substituent effects. The fragmentation pathways for each of the tautomers were determined using high-resolution mass spectrometry.M. V. Lomonosov Moscow State University, 119899 Moscow. Yerevan State University, 375025 Yerevan. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp 1525–1530, November, 1995 Original article submitted November 1, 1995.     

Magnetic properties of Cu(II) bischelate complexes with 3-imidazoline nitroxides. 2. Anab initio analysis of exchange interaction mechanisms

The mechanism responsible for the emergence of ferromagnetic exchange interactions in bischelate complexes of Cu²⁺ with enaminoketone derivatives of 3-imidazoline nitroxide CuL₂ is studied by ab initio quantum chemical methods. The parameters J_cu-L and J_L-L’ of exchange interactions between the unpaired electrons of the paramagnetic centers (Cu²⁺ ion and N-O groups of nitroxyl ligands L and L’) of these complexes were calculated in terms of the full 3x3 configuration interaction between the singlet states constructed in a basis set of molecular orbitals of unpaired electrons. It is shown that for variations of the structure of the coordination polyhedron around the Cu²⁺ ion from square planar to tetrahedral the exchange interactions between the unpaired electrons of the paramagnetic centers is ferromagnetic J_Cu-L >J_L -L’>0, which agrees with the data of magnetic measurements. The principal mechanism of exchange interactions in CuL₂ complexes is the delocalization mechanism that is due to a minor transfer of spin density from the 3d-orbitals of Cu²⁺ to the Σ-orbitals of the N-O groups of L and L’ ligands. Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 5, pp. 850–856, September-October, 1997.     

Crystal structure of cobalt(II) complexes with imidazoline nitroxide

The crystal structures of Co(II) coordination compounds CoL ₂-α modification (I), CoL₂(CH₃OH)₂ (II), and CoL₂Py₂(III) — where L is a stable nitroxide 4-(3′,3′,3′-trifluoro-2′-oxypropylene)-2,2,5,5-tetramethyl-3-imidazoline-l-oxyl (L), were determined. It was found that the tetrahedral surroundings of cobalt in I consist of the O and N donor atoms of the deprotonated enaminoketone groups of L. In II and III, the same atoms form the equatorial plane of the centrosymmetric octahedral environment of the central atom in which the axial positions are occupied by the methanol O atoms or the pyridine N donor atoms. In the octahedral coordination centers of II and III, the Co-O and Co-N distances exceed analogous distances in the tetrahedral coordination center of I, substantially increasing the chelate angle in I compared to II and III. In I, the Co-O and Co-N bond lengths and the OCoN chelate angles are, respectively, 1.921(4), 2.006(4) Å, 93.6(2)° in II, 2.014(4), 2.177(4), Co-O_OH 2.146(4) Å, 86.9(2)° in the two crystallographically independent molecules of III, 2.031(2) and 2.022(2), 2.170(2) and 2.193(2), Co-N_Py 2.213(2) and 2.219(2)Å, 87.04(7) and 87.20(7)°. Compounds I and III are molecular. Compound II in the solid state has a layered polymer structure due to hydrogen bonding between the O atoms of the nitroxyl groups of L and the O atoms of the coordinated alcohol molecules.