A novel route to spin-labeled dihydrooxepines and o-benzoquinones

A reaction of a lithiated derivative of 4,4,5,5-tetramethyl-3-oxido-4,5-dihydro-1H-imidazole 1-oxyl with 3,6-di-tert-butyl-o-benzoquinone at ?80 °C predominantly gave spin-labeled dihydrooxepine via nucleophilic 1,2-addition of the paramagnetic carbanion to the CO group of the benzoquinone followed by insertion of the O atom into the ring. At lower temperatures, this reaction was accompanied by 1,4-addition of the organolithium compound to the benzoquinone followed by oxidation of the resulting adduct into spin-labeled o-benzoquinone. This ??one pot?? process is a novel approach to organic derivatives that can further be converted into di- and polyradicals combining nitronyl nitroxide and semiquinolate fragments.     

Heterospin Copper(II) Catecholate Complex with the TEMPO–Iminopyridine Ligand

Russian Journal of Coordination Chemistry - The heterospin copper(II) complex, ((pyridin-2-ylmethylene)-4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl)-3,6-di-tert-butylcatecholatocopper(II) (I), is...     

"Jumping crystals": oxygen-evolving metal-nitroxide complexes

The crystals of heterospin complexes [M(hfac)(2)L(2)] (where M = Cu, Ni, Co, or Mn; hfac = hexafluoroacetylacetonate; and L = nitronyl nitroxide, 4,4,5,5-tetramethyl-2-(1-methyl-1H-imidazol-5-yl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl) were found to make unusual jumping motions. Under ambient conditions, the jumping and various displacements of crystals lasted for several weeks. The mechanical motion was accompanied by the cracking and disintegration of crystals, and a solid [M(hfac)(2)(L(1))(2)] complex with the corresponding imino nitroxide 4,4,5,5-tetramethyl-2-(1-methyl-1H-imidazol-5-yl)-4,5-dihydro-1H-imidazole-1-oxyl (L(1)) was detected. The jumping was accompanied by the spontaneous elimination of oxygen, the source of which was the nitronyl nitroxyl fragment of coordinated L. An X-ray study of [M(hfac)(2)L(2)] (where M = Cu, Ni, Co, or Mn) showed that the molecular structure of all [M(hfac)(2)L(2)] and their packing in the solid state were identical. The packing of [M(hfac)(2)L(2)] was concluded to be critical to the mechanical effect. In complexes with different stoichiometries or different sets of diamagnetic ligands ([Cu(hfac)(2)L](2), [Cu(hfac)(acac)L]·EtOH, [CuPiv(2)L(2)]·2CH(2)Cl(2), and [Cu(hfac)(2)L(2)Cu(2)Piv(4)]·3C(7)H(8) (where acac is acetylacetonate and Piv is trimethylacetate), or free L), the effect vanished when the packing changed.     

Synthesis and characterization of Li(I)-M(II) (M = Co, Ni) heterometallic complexes as molecular precursors for LiMO2

Lithium-containing heterometallic complexes with cobalt (Li₂Co₂(Piv)₆(2,4-Lut)₂ (2, Piv is the pivalate anion) and Li₂Co₂(O₂CCH₂Bu^t)₆(2,4-Lut)₂ (3)) and with nickel (Li₂Ni₂(Piv)₆(DME)₂ (4) and Li₂Ni₂(Piv)₆(2,2′-bpy)₂ (5)) were synthesized. The structures of the complexes were established by X-ray diffraction. The magnetic properties of complexes 2 and 4 were studied. The thermal behavior of compounds 2, 3, and 5 was investigated. It was shown that the compounds under study can be used as molecular precursors for the synthesis of lithium cobaltate and nickelate.     

New high-spin iron complexes based on bis(imino)acenaphthenes (BIAN): synthesis,structure, and magnetic properties

The reactions of iron diiodide with one and two equivalents of the monopotassium salt of 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-BIAN) in diethyl ether gave the complexes [(dpp-BIAN)FeI]₂ (1) and (dpp-BIAN)₂Fe (2), respectively. The bis-ligand complex (tms-BIAN)₂Fe (3) was synthesized by the exchange reaction of the monosodium salt of 1,2-bis(trimethylsilylimino)acenaphthene (tms-BIAN) with iron diiodide. The reaction of FeI₂ with tms-BIAN affords the chelate complex (tms-BIAN)FeI₂ (4), whereas the reaction of FeBr₂·2H₂O with tms-BIAN is accompanied by elimination of trimethylsilyl groups to form the tris-ligand acenaphthene-1,2-diimine complex [(H₂BIAN)₃Fe][FeBr₃·THF]₂ (5) containing two types of iron ions. Compounds 1–5 were characterized by IR spectroscopy and elemental analysis. The molecular structures of 1–5 were determined by single-crystal X-ray diffraction. For high-spin complexes 1–3, the temperature-dependent magnetic susceptibilities were measured in the range of 4–300 K.     

Synthesis, X-ray spectral, and magnetochemical study of copper complexes based on tridentate azomethines of 3-allylsalicylaldehyde

Tridentate azomethine ligands (H₂L) based on 3-allylsalicylaldehyde and o-aminophenol, o-aminothiophenol, or 2-ethylamino-5-nitroaniline were synthesized and identified by IR and ¹H NMR spectroscopies. The structure of complexes (Ia-Ic) was studied by magnetochemistry and EXAFS spectroscopy. Complexes Ia and Ib (X = O, S) are binuclear and exhibit antiferromagnetic exchange interaction: 2J = ?36.5 and ?950 cm^?1, respectively. Complex Ic (X = NC₂H₅) is mononuclear (μ_eff = 1.75 μ_B at 275 K and does not change as temperature decreases).     

Novel Dinuclear Redox‐isomeric Complexes with a Tetrapodal Pyridine‐based Ligand

Tris‐o‐semiquinonato cobalt complexes react with a tetrapodal pyridine‐derived ligand to form dinuclear cobalt compounds of general formula (OMP)[CoQ₂]₂, where OMP = 2,2′‐(pyridine‐2,6‐diyl)bis(N¹,N¹,N³,N³‐tetramethylpropane‐1,3‐diamine), Q = mono‐ or dianion of 3,6‐di‐tert‐butyl‐o‐benzoquinone (complex 1 ) and it derivatives: 3,6‐di‐tert‐butyl‐4,5‐N,N′‐piperazino‐o‐benzoquinone (complex 2 ), and 3,6‐di‐tert‐butyl‐4‐Cl‐o‐benzoquinone (complex 3 ). Single crystal X‐ray crystallography of 1 and 3 indicates two bis‐quinonato cobalt units bound by an OMP ligand, which acts as a bridge. Each central cobalt atom is chelated by one N¹,N¹,N³,N³‐tetramethylpropane‐1,3‐diamine and two o‐quinonato fragments. The nitrogen atom of the pyridine ring is uncoordinated. All complexes were characterized by NIR‐IR and EPR spectroscopy, precise adiabatic vacuum calorimetry, and by variable‐temperature magnetic susceptibility measurements. All data indicate a reversible thermally driven redox‐isomeric (valence tautomeric) transformation in the solid state for all complexes.     

Synthesis, structure, electrochemical and magnetic properties of 2,6-bis(5-trifluoromethylpyrazol-3-yl)pyridine and its NiII complexes

2,6-Bis(5-trifluoromethylpyrazol-3-yl)pyridine (H₂L) and its mono-, tri-, and tetranuclear NiII complexes were synthesized for the first time. All the obtained compounds were characterized by single-crystal X-ray diffraction analysis. In the complexes, 2,6-bis(5-trifluoromethylpyrazol-3-yl)pyridine exists in the neutral and dianionic forms and exhibits different coordination modes (??³-, ??²-??³:??¹-, and ??³-??³:??¹:??¹). The electrochemical and magnetic properties of all compounds were studied. The tetranuclear Ni^II complex with the L^2? dianion is reduced in two sequential reversible one-electron steps.     

Syntheses, structures, and properties of the Co(II), Ni(II), and Cu(II) complexes with 5-carboxy- and 5-methoxycarbonylpyrazoles

New cobalt(II), nickel(II), and copper(II) complexes based on 5-methoxycarbonyl-3-me-thylpyrazole (MePzCOOMe), [Co(MePzCOOMe)₂(H₂O)₂](NO₃)₂ (I), [Ni(MePzCOOMe)₂(H₂O)₂] (NO₃)₂ (II), and [Cu(MePzCOO)₂(H₂O)] · 3H₂O (III), were synthesized. The compounds were studied by X-ray diffraction analysis, IR spectroscopy, and static magnetic susceptibility. The molecular and crystal structures of complexes I and III were determined by X-ray structure analysis.     

Synthesis, molecular and electronic structure of an incomplete cuboidal Re3S4 cluster with an unusual quadruplet ground state

A Re(IV) cluster complex [Re(3)(μ(3)-S)(μ-S)(3)(dppe)(3)Br(3)](+) with nine cluster skeletal electrons (CSE) and a quadruplet ground state has been prepared by treatment of [Re(3)S(7)Br(6)]Br with 1,2-bis(diphenylphosphino)ethane (dppe) in MeCN.