Synthesis,Structure, and Magnetic Properties of Heterospin Polymers MI[MII(Hfac)L2]

Russian Journal of Coordination Chemistry - Heterospin polymeric complexes based on Ni(II) and Co(II) hexafluoroacetylacetonates and deprotonated iminonitroxide,...     

Searching for Neutrino and Ultra-High-Energy Gamma-Ray Counterparts of the GCN Alerts

Physics of Atomic Nuclei - The Baksan Neutrino Observatory setups are currently performing search for neutrino and ultra-high-energy gamma-ray counterparts of the events on the Gamma-ray...     

Kinetic description of the hydrogenation of nitrobenzene and nitrosobenzene on skeletal nickel in aqueous solutions of propan-2-ol of different compositions

The kinetics of the hydrogenation of nitrosobenzene and nitrobenzene is simulated taking into account accompanying processes and specific features of the conversion of reactive groups. The constants of the hypothetical reaction steps are calculated. The influence of sodium hydroxide and acetic acid on the kinetic parameters of the reactions is discussed.     

Stereo sensitivity of exchange interactions in Ni<Superscript>II</Superscript> and Cu<Superscript>II</Superscript> heterospin complexes with 5-formylpyrrolyl-substituted nitroxides

5-Formylpyrrolyl-substituted nitronyl and imino nitroxide radicals HL¹ and HL² were synthesized. Their solid phases are formed by packing pairs of the molecules. In the {HL¹...HL¹} pairs, the dominant interaction is the ferromagnetic exchange with J/kB = 8.8 K (Hamiltonian \(H = 2J\left( {\overrightarrow {{s_1}} \overrightarrow {{s_2}} } \right)\)). The ferromagnetic exchange occurs also in the heterospin molecules [Ni(L¹)₂], [Cu(L¹)₂], and [Ni(L²)₂(MeOH)₂]. In the complexes [Ni(L¹)₂] and [Cu(L¹)₂], a small change in the mutual orientation of the coordinated ligands has a considerable effect on the value and the sign of the energy of exchange interactions between the unpaired electrons of the metal ion and paramagnetic ligands.     

Solid state NMR characterization of individual compounds and solid solutions formed in Sc(2)O(3)--V(2)O(5)--Nb(2)O(5)--Ta(2)O(5) system

In this study, (51)V, (45)Sc and (93)Nb MAS NMR combined with satellite transition spectroscopy analysis were used to characterize the complex solid mixtures: VNb(9(1-x))Ta(9x)O(25), ScNb((1-x))Ta(x)O(4) and ScNb(2(1-x))Ta(2x)VO(9) (x = 0, 0.3, 0.5, 0.7, 1.0). This led us to describe the structures of Sc and V sites. The conclusions were based on accurate values for (51)V quadrupole coupling and chemical shift tensors obtained with (51)V MAS NMR/SATRAS for VNb(9)O(25), VTa(9)O(25) and ScVO(4). The (45)Sc NMR parameters have been obtained for Sc(2)O(3), ScVO(4), ScNbO(4) and ScTaO(4). On the basis of (45)Sc NMR and data available from literature, the ranges of the (45)Sc chemical shift have been established for ScO(6) and ScO(8). The gradual change of the (45)Sc and (51)V NMR parameters with x confirms the formation of solid solutions in the process of synthesis of VNb(9(1-x))Ta(9x)O(25) and ScNb((1-x))Ta(x)O(4), in contrast to ScNb(2(1-x))Ta(2x)VO(9). The cation sublattice of ScNb((1-x))Ta(x)O(4) is found to be in octahedral coordination. The V sites in VNb(9(1-x))Ta(9x)O(25) are present in the form of slightly distorted tetrahedra. The (93)Nb NMR parameters have been obtained for VNb(9)O(25).     

Crystal chemistry of mercury(I) and mercury(I, II) minerals

The crystal structures of 16 mercury(I)- and mercury(I, II)-containing minerals having (Hg-Hg)²⁺ groups are considered. The Hg-Hg and Hg-X bond lengths and the HgHgX angles (X = Cl, Br, I, O, S) are analyzed. A comparative crystal chemical analysis of the environment of Hg atoms is carried out. The Hg-Hg and Hg-X distances vary within 2.43-2.60 and 1.93-2.43 å, respectively; the angles defining the deviation of the X-Hg-Hg-X groups from linearity are from 146 to 177?. In most cases, the coordination environment of the mercury atoms involves the metal atom of the (Hg-Hg)²⁺ dumbbell and the X atom, but in several compounds the coordination number of the mercury atoms increases due to the additional atoms lying 2.5–3.5 å away. In terlinguaite and kuznetsovite, the Hg₃ triangle is rather unusual; in the latter mineral, the Hg-Hg bonds are lengthened to 2.64-2.70 å. The review covers structural data up to May 1997.     

Synthesis, structure, and magnetic properties of (6-9)-nuclear Ni(II) trimethylacetates and their heterospin complexes with nitroxides

New polynuclear nickel trimethylacetates [Ni6(OH)4(C5H9O2)8(C5H10O2)4] (6), [Ni7(OH)7(C5H9O2)7(C5H10O2)6(H2O)] x 0.5 C6H14 x 0.5 H2O (7), [Ni8(OH)4(H2O)2(C5H9O2)12] (8), and [Ni9(OH)6(C5H9O2)12(C5H10O2)4] x C5H10O2 x 3 H2O (9), where C5H9O2 is trimethylacetate and C5H10O2 is trimethylacetic acid, have been found. Their structures were determined by X-ray crystallography. Because of their high solubility in low-polarity organic solvents, compounds 6-9 reacted with stable organic radicals to form the first heterospin compounds based on polynuclear Ni(II) trimethylacetate and nitronyl nitroxides containing pyrazole (L(1)-L(3)), methyl (L(4)), or imidazole (L(5)) substituent groups, respectively, in side chain [Ni7(OH)5(C5H9O2)9(C5H10O2)2(L(1))2(H2O)] x 0.5 C6H14 x H2O (6+1a), [Ni7(OH)5(C5H9O2)9(C5H10O2)2(L2)2(H2O)] x H2O (6+1b), [Ni7(OH)5(C5H9O2)9(C5H10O2)2(L(3))2(H2O)] x H2O (6+1c), [Ni6(OH)3(C5H9O2)9(C5H10O2)4(L(4))] x 1.5 C6H14 (6'), and [Ni4OH)3(C5H9O2)5(C5H10O2)4(L(5))] x 1.5 C7H8 (4). Their structures were also determined by X-ray crystallography. Although Ni(II) trimethylacetates may have varying nuclearity and can change their nuclearity during recrystallization or interactions with nitroxides, this family of compounds is easy to study because of its topological relationship. For any of these complexes, the polynuclear framework may be derived from the [Ni6] polynuclear fragment {Ni6(mu4-OH)2(mu3-OH)2(mu2-C5H9O2-O,O')6(mu2-C5H9O2-O,O)(mu4-C5H9O2-O,O,O',O')(C5H10O2)4}, which is shaped like an open book. On the basis of this fragment, the structure of 7-nuclear compounds (7 and 6+1a-c) is conveniently represented as the result of symmetric addition of other mononuclear fragments to the four Ni(II) ions lying at the vertexes of the [Ni6] open book. The 9-nuclear complex is formed by the addition of trinuclear fragments to two Ni(II) ions lying on one of the lateral edges of the [Ni6] open book. This wing of the 9-nuclear complex preserves its structure in another type of 6-nuclear complex (6') with the boat configuration. If, however, two edge-sharing Ni(II) ions are removed from [Ni6] (one of these lies at a vertex of the open book and the other, on the book-cover line), we obtain a 4-nuclear fragment recorded in the molecular structure of 4. Twinning of this 4-nuclear fragment forms highly symmetric molecule 8, which is a new chemical version of cubane.     

Copper(II) bis(hexafluoroacetylacetonate) complexes with 2-(2-methyltetrazolyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole 1-oxides

An efficient procedure was developed for the synthesis of alkyltetrazolyl-substituted nitronyl nitroxides (L ¹ and L ²). These compounds were used to prepare the first alkyltetrazolyl-substituted imino nitroxides (L ³ and L ⁴). The molecular structures of L ³ and L ⁴ were confirmed by X-ray diffraction. Investigation of the products prepared by the reaction of copper(II) bis(hexafluoroacetylacetonate), Cu(hfac)₂, with nitroxides made it possible to divide ligands L ¹—L ⁴ into two groups. The reactions of spin-labeled tetrazoles L ¹—L ³ with Cu(hfac)₂ afford the heterospin complexes Cu(hfac)₂L₂, whereas L ⁴ serves as a bidentate ligand in the Cu(hfac)₂ L ⁴ complex. In the solid Cu(hfac)₂L₂ complexes, antiferromagnetic exchange interactions between the unpaired electrons of the nitroxide fragments of the adjacent molecules prevail, due to which μ_eff decreases with decreasing temperature, and the spins of nitroxides are completely compensated at 5–10 K. The Cu(hfac)₂ L ⁴ complex displays strong intramolecular ferromagnetic coupling, due to which μ_eff at room temperature is close to 2.9 μ_B. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 64–70, January, 2006.     

Heterospin complexes based on dinuclear CuII triketonate and nitroxides

Heterospin complexes of bis(μ₂-1,1,2,2,8,8,9,9-octafluorononane-3,5,7-trionato)dicopper(II) ([Cu₂L₂]) with nitronyl nitroxides 2-(1-methyl-1H-pyrazol-4-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl 3-oxide (2) and 4,4,5,5-tetramethyl-2-(3-pyridinyl)-4,5-dihydro-1H-imidazole-1-oxyl 3-oxide (1) were synthesized and structurally characterized. Crystals of the complexes are formed by the discrete bis[1-methyl-4-(4,4,5,5-tetramethyl-3-oxide-1-oxyl-4,5-dihydro-1H-imidazol-2-yl)-1H-pyrazole]-bis (μ₂-1,1,2,2,8,8,9,9-octafluorononane-3,5,7-trionato)dicopper(II) etherate (3) and bis[3-(4,4,5,5-tetramethyl-3-oxide-1-oxyl-4,5-dihydro-1H-imidazol-2-yl)pyridine]-bis (μ₂-1,1,2,2,8,8,9,9-octafluorononane-3,5,7-trionato)dicopper(II) (4) molecules. Each Cu atom of the dinuclear chelate fragment coordinates one paramagnetic ligand through the N atom of the pyrazole or pyridine fragment, respectively. In complex 3, the paramagnetic ligands are located on one side of the plane of the chelate fragment, whereas the ligands in complex 4 are located above and below the plane of the chelate fragment. The magnetic properties of complexes 3 and 4 are determined by dominant antiferromagnetic exchange interactions between the unpaired electrons of the Cu^II atoms in the dinuclear Cu₂L₂ moiety. Dedicated to Academician O. M. Nefedov on the occasion of his 75th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1836–1840, November, 2006.