Crystal Structure of Copper(II) and Cobalt(II) Hexafluoroacetylacetonate Complexes with 2,2,5,5-Tetramethyl-4-phenyl-3-imidazoline-1-oxyl-3-oxide

The crystal structures of the copper(II) and cobalt(II) hexafluoroacetylacetonate complexes with the nitroxide 2,2,5,5-tetramethyl-4-phenyl-3-imidazoline-1-oxyl-3-oxide (PhImOx) Cu(hfac)₂(PhImOx), Co(hfac)₂(PhImOx), and Co(hfac)₂(PhImOx)₂ have been determined. The former two are chain type complexes, whereas the latter has a molecular structure. The coordination polyhedra of the copper and cobalt atoms are tetragonally distorted octahedra. In the two chain type compounds, the octahedra are formed from the hfac anion, nitroxyl, and N-oxide O atoms; in the molecular complex, the O atoms of the NO groups are not coordinated to the metal atoms. In the structure of Cu(hfac)₂(PhImOx), F...F contacts equal to 2.805 have been found.     

Weak-localization effect for light backscattered by surfaces with a complex structure

Results of laboratory measurements of the weak-localization effect for light scattered by surfaces with different characteristics are presented. The measurements were made in a range of phase angles of 0.2°–3.5°. The aim of the measurements was to study the influence of the choice of surface material (metal, dielectric), the size of particles of the scattering surface, their packing density, the reflectivity of a sample, and the wavelength of incident radiation on the effect. For the measurements, both nonpolarized and linearly polarized light was used. Powders of dielectric materials were found to enhance the weak-localization effect with increasing particle size, but the effect weakened starting with a certain size of the order of wavelength. The pressing of powders of dielectric transparent materials enhanced the opposition effect. This was most pronounced for samples with small-sized particles. The phase dependence of brightness became wider and more linear with decreasing reflectivity of the surface. A qualitative difference in the behavior of the phase dependence for the ratio of cross-and copolarized components was observed. For metals and metal-like materials, the ratio increased with decreasing phase angle. Dielectrics were found to have an opposite dependence.     

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.     

Interpretation of X-ray photoelectron spectra of free nitroxyl radicals

N1s and O1s X-ray photoelectron spectra of stable nitroxyl radicals (substituted piperidine-1-oxyl, 2-imidazoline-1-oxyl, and 2-imidazoline-3-oxide-1-oxyl) and also diamagnetic derivatives with a {ONCNO} fragment are measured. It is shown that the structure of N1s and O1s X-ray photoelectron spectra of nitroxyls is determined by charge transfer processes between different parts of the molecule to screen the X-ray hole and the spin-spin interaction of unpaired electrons on the HOMO and 1s level.     

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.     

Molecular magnets based on chain polymer complexes of copper(II) bis(hexafluoroacetylacetonate) with isoxazolyl-substituted nitronyl nitroxides

First isoxazolyl-substituted nitronyl nitroxides (L and $L^{Me_2 }$ ) were synthesized and characterized. Their reactions with Cu(hfac)₂ and Mn(hfac)₂ (hfac is hexafluoroacetylacetonate) afford the heterospin complexes [Cu(hfac)₂L] _n , [Cu₂(hfac)₄L] _n , $\left[ {Cu_2 (hfac)_4 L^{Me_2 } } \right]_n$ , $\left[ {Cu(hfac)_2 L^{Me_2 } } \right]_n$ , $\left[ {Cu(hfac)_2 L^{Me_2 } _2 } \right]$ , $\left[ {Cu(hfac)_2 L^{Me_2 } (MeCN)} \right]$ , [Mn(hfac)₂]₃L₄, and $\left[ {Me(hfac)_2 L^{Me_2 } } \right]_2$ . In the ligand L, the N atom of the isoxazole ring (NIz) has weak electron-donating properties. For example, the paramagnetic ligand in the chain polymer complex [Cu(hfac)₂L] _n acts as a bidentate bridging ligand coordinated through both O atoms of the nitronyl nitroxide group (O_N-O); the N_Iz and O_Iz atoms are not involved in the coordination. The introduction of Me groups into the isoxazole substituent results in an increase in the electron density on the N_Iz atom and enables the synthesis of the chain polymer complex $\left[ {Cu(hfac)_2 L^{Me_2 } } \right]_n$ , in which the bidentate bridging ligand $L^{Me_2 }$ is coordinated through the O_N-O and N_Iz atoms. In the mononuclear complexes $\left[ {Cu(hfac)_2 L^{Me_2 } _2 } \right]$ and $\left[ {Cu(hfac)_2 L^{Me_2 } (MeCN)} \right]$ , the paramagnetic ligand is coordinated only through the N_Iz atom. The solid heterospin Mn complexes [Mn(hfac)₂]₃L₄ and $\left[ {Mn(hfac)_2 L^{Me_2 } } \right]_2$ have a molecular structure. In these complexes, strong antiferromagnetic intracluster exchange interactions arise. The residual magnetic moments of the exchange clusters in the complex [Mn(hfac)₂]₃L₄ are ferromagnetically coupled, resulting in the increase in the effective magnetic moment (??_eff) of the complex with decreasing temperature in the range of 300??30 K. The thermomagnetic study of the complexes [Cu(hfac)₂L] _n , [Cu₂(hfac)₄L] _n , and $\left[ {Cu_2 (hfac)_4 L^{Me_2 } } \right]_n$ in the range of 2?C300 K revealed the ferromagnetic ordering at temperatures below 5 K. The ESR study of the solid complex $\left[ {Cu(hfac)_2 L^{Me_2 } } \right]_n$ showed that the decrease in its ??_eff in the temperature range of 30?C300 K is associated with the direct exchange interaction between the unpaired electrons of the nitronyl nitroxides of adjacent chains, whereas at temperatures below 30 K, only Cu²⁺ ions contribute to the magnetic susceptibility of the complex.     

Synthesis, structure, and properties of a new representative of the family of calix[4]arene-containing [MnII 2MnIII 2]-clusters

A new representative of calix[4]arene-containing tetranuclear manganese complexes of the [Mn^II ₂Mn^III ₂] type was obtained. According to the data of magnetoochemical studies, the complex exhibits properties of molecular magnet at the temperature below 5 K. Parameters of the exchange interaction and the activation energy were determined. The influence of the peripheral environment on the magnetic properties of the tetranuclear manganese framework in the structure of the complex was revealed.