Crystal Structure and Magnetic Properties of Pyridyl-Substituted Nitronyl Nitroxides

X-ray crystal structure and cryomagnetic properties of three organic radicals, 2-(2-pyridyl)-4, 4,5,5-tetramethyl-4,5-dihydro-1-H-imidazol-1-oxyl-3-N-oxide(NIT-oPy) 1, 2-(3-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-l-H-imidazol-1-oxyl-3-N-oxide(NIT-mPy) 2 and 2-(6-methyl-2-pyridyl)-4,4,5,5-tetramethyl-4, 5-dihydro-1-H-imidazol-1-oxyl-3-N-oxide(NIT-6M-oPy) 3 were investigated. The crystal structures of compounds 1-3 show the same feature of a P2₁/c space group of a monoclinic system. Two crystallographically independent molecules were found in the crystals of compounds 1-3. The temperature dependence of magnetic susceptibility of compounds 1-3 revealed an intermolecular antiferromagnetic exchange interaction.     

Synthesis,Structure and Magnetic Properties of dimeric Nickel(II) Benzoate with Pyridyl‐substituted Nitronyl Nitroxides

The novel heterospin complex [Ni₂(PhCOO)₄(NITpPy)₂]·2CH₃CN ( 1 ) was synthesized by the reaction of nickel benzoate and 2‐(4‐pyridyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide (NITpPy) in acetonitrile and dichloromethane solutions. The X‐ray structure determination shows that complex 1 consists of a symmetrical dimeric Ni^II benzoate paddle‐wheel core and pyridyl nitrogen atoms of radical ligands at the apical position, in addition, the temperature (2–300K) dependent magnetic susceptibility measurements indicate that 1 has antiferromagnetic behavior.     

Synthesis,Structure and Magnetic Properties of 1‐D Silver(I) Complexes with Benzoic Acids Bearing Ortho‐Imino Nitroxide and Para‐Nitronyl Nitroxide Radical Ligands

Two new 1‐D silver( I ) complexes, [Ag( I )1.5(IM‐oBA)(NO₃)0.5] ( 1 ) and [Ag( I )(NIT‐pBA)] ( 2 ), (IM‐oBAH = 2‐(2‐carboxyphenyl)‐4,4,5,5‐tetramethyl‐4,5‐dihydro‐1H‐imidazol‐1‐yloxyl, NIT‐pBAH = 2‐(4‐carboxyphenyl)‐4,4,5,5‐tetramethyl‐4,5‐dihydro‐3‐oxido‐H‐imidazol‐3‐ium‐1‐yloxyl) have been prepared and structurally characterized. Complexes 1 and 2 crystallized in the monoclinic space groups of C2/c and P2₁/c, respectively. In complex 1 , the structure consists of trinuclear Ag(I) atoms with different linkages of IM‐oBA and nitrates. The trinuclear Ag(I) atoms are further coordinated to the neighbor IM‐oBA radicals via self‐assembly of the nitrogen atom of imine moiety and extended into formation of a polymeric chain. Complex 2 is constructed from a bis(carboxylato‐O,O')‐bridged centrosymmetric dimeric subunit and extended into a polymeric chain through self‐assembly coordination between metal ions and nitroxide groups of NIT‐pBA radicals. Temperature dependence of magnetic susceptibility measurements showed a weak ferromagnetic coupling between nitroxide radicals in 1 and 2 with J = 5.62 for 1 and 6.62 cm^?1 for 2 , respectively.     

Syntheses,Structures, and Properties of Two New Tri‐spin Lanthanide‐Nitronyl Nitroxide (LnIII = GdIII and HoIII) Complexes

Abstract. Two radical–Ln^III–radical complexes, [Ln(hfac)₃(NITPh‐Ph)₂] [Ln = Gd ( 1 ) and Ho ( 2 ), hfac = hexafluoroacetylacetonate; and NITPh‐Ph = 4′‐biphenyl‐4, 4, 5, 5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide] were synthesized and characterized by X‐ray diffraction, elemental analysis, magnetic measurements, as well as IR and UV/Vis spectroscopy. X‐ray crystal structure analysis revealed that the structures of both complexes are isomorphous, the central Ln^III ions are coordinated by six oxygen atoms from three hfac ligand molecules and two oxygen atoms from nitronyl radicals. The temperature dependencies of the magnetic susceptibilities were studied. They showed that in the Gd^III complex, ferromagnetic interactions between Gd^III and the radicals and antiferromagnetic interactions between the radicals coexist in this system (with J_Rad–Gd = 0.1 cm^–1, J_Rad–Rad = –0.309 cm^–1).     

Crystal Structure and Magnetic Properties of a Copper(II) Chloride Complex with Nitronyl Nitroxide

A new compound [Cu(NITPhCH₃)₂Cl₂] (NITPhCH₃ 2-(4-methyl-phenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide) has been characterized spectroscopically. A crystal structure analysis has shown the copper ion to be planar, coordinated by two chlorine atoms and two oxygen (nitroxyl) atoms. Based on magnetic susceptibility measurements the compound was found to exhibit a moderately strong antiferromagnetic interaction (J= m 107.44 cm_-1) between copper(II) and the radical.     

Strong Antiferromagnetic Exchange Interactions in Cobalt(II) Complexes with 2-Pyridyl Substituted Nitronyl Nitroxide Ligand

Three new complexes, [Co(hfac)₂(NIToPy)] (1), [CoCl₂(NIToPy)₂] (2), and [Co(NIToPy)₃](ClO₄)₂ (3), with NIToPy = 2-(2-Pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-oxy-3-oxide, and hfac = hexafluoroacetylacetonate, have been synthesized. The compound 3 crystallized in the monoclinic space group P2₁, with two molecules in a unit cell of dimensions a = 10.565(4) Å, b = 14.714(9) Å, c = 14.596(7) Å, and β = 107.10(4)°. The temperature-dependent magnetic susceptibility measurements (4.2 K-300 K) for the complexes demonstrated strong antiferromagnetic exchange interaction between cobalt(II) ion and NIToPy radical spins with J = ?140.1 cm^?1 for 1, J = ?94.2 cm^?1 for 2, and J = ?161.8 cm^?1 for 3, respectively. The magneto-structural correlation in these complexes has been discussed.     

Four Discrete Transition Metal Complexes Involving Pyridyl‐substituted Nitronyl Nitroxide: Syntheses,Crystal Structures,and Magnetic Properties

Four discrete metal‐radical complexes, [Cu(p‐MePh‐COO)₂(NITpPy)₂] ( 1 ), [Ni(m‐MePhCOO)₂(NITpPy)₂(H₂O)₂] · (CH₃‐OH)₂ ( 2 ), [Mn(p‐MePhCOO)₂(NITpPy)₂(H₂O)₂] ( 3 ), and [Mn(m‐MePhCOO)₂(NITpPy)₂(H₂O)₂] ( 4 ) [NITpPy = 2‐(4‐pyridyl)‐4,4,5,5‐tetramethyl‐4,5‐dihydro‐1H‐imidazolyl‐1‐oxyl‐3‐oxide] were synthesized and characterized by elemental analyses, IR spectroscopy, PXRD, single‐crystal X‐ray diffraction, and magnetic susceptibility. For the four complexes, the crystal structural analyses indicate that the two radical ligands coordinated to the metal ions by the nitrogen atoms of the pyridine rings form three spin complexes, where toluates act as co‐ligands. Weak antiferromagnetic interactions [J_Cu–Rad = –6.75 cm^–1 ( 1 ), J_Co–Rad = –4.15 cm^–1 ( 2 ), J_Mn–Rad = –0.22 cm^–1 ( 3 ), and J_Mn–Rad = –3.74 cm^–1 ( 4 )] were observed, spin polarization mechanism and orbital symmetry are used to explain the magnetic coupling in these complexes.     

Synthesis,Crystal Structures,and Magnetic Properties of Two Copper(II) Radical Heterospin Complexes

Two heterospin complexes [Cu(NIT3Py)(cda)H₂O] · H₂O ( 1 ) and [Cu(NIT2Py)(cda)H₂O] · H₂O · CH₃OH ( 2 ) with Cu^II ions and pyridyl‐substituted nitronyl nitroxide radicals (NITxPy = 2‐(x′‐pyridyl)‐4,4,5,5‐tetramethyl‐imidazoline‐1‐oxyl‐3‐oxide, x = 3, 2; H₂cda = 4‐hydroxy‐pyridine‐2,6‐dicarboxylic acid) were synthesized and characterized structurally and magnetically. The single crystal structures show that the two complexes are both two‐spin complexes, in which the different radicals make the two complexes have different hydrogen bonding interactions to form 2D and 1D supramolecular network for complexes 1 and 2 , respectively. The magnetic measurements indicate that complexes 1 and 2 both exhibit antiferromagnetic interactions between Cu^II and radicals.     

Synthesis,Crystal Structure,and Magnetic Property of New Trispin Ln(III)‐Nitronyl Nitroxide Complexes

Four Ln(III) complexes based on a new nitronyl nitroxide radical have been synthesized and structurally characterized: {Ln(hfac)₃[NITPh(MeO)₂]₂} (Ln = Eu( 1 ), Gd( 2 ), Tb( 3 ), Dy( 4 ); NITPh(MeO)₂ = 2‐(3′,4′‐dimethoxyphenyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide; hfac = hexafluoroacetylacetonate). The single‐crystal X‐ray diffraction analysis shows that these complexes have similar mononuclear trispin structures, in which central Ln(III) ion is eight‐coordinated by two O‐atoms from two nitroxide groups and six O‐atoms from three hfac anions. The variable temperature magnetic susceptibility study reveals that there exist ferromagnetic interactions between Gd(III) and the radicals, and antiferromagnetic interactions between two radicals (J_Gd‐Rad = 3.40 cm^?1, J_Rad‐Rad = ?9.99 cm^?1) in complex 2 . Meanwhile, antiferromagnetic interactions are estimated between Eu(III) (or Dy(III)) and radicals in complexes 1 and 4 , and ferromagnetic interaction between Tb(III) and radicals in complex 3 , respectively.     

Three Nickel(II) and Zinc(II) Complexes with Two Novel Nitronyl Nitroxide Ligands: Syntheses,Crystal Structures,and Luminescent Properties

To explore the coordination abilities of nitronyl nitroxide ligands, two ligands substituted with quinoxaline ( L¹ ) and 2‐phenyl‐1, 2, 3‐triazole ( L² ) and their Ni^II and Zn^II complexes: Ni( L¹ )(hfac)₂ ( 1 ), Ni( L² )(hfac)₂ ( 2 ), and Zn( L² )(hfac)₂ ( 3 ) (hfac = hexafluoroacetylacetonate), were synthesized and characterized. X‐ray single‐crystal diffraction analysis shows that compound 1 has a mononuclear structure, which is further linked into a three‐dimensional (3D) supramolecular network by C–H ··· F hydrogen‐bonding, C–H ··· π, and π ··· π stacking interactions. Complexes 2 and 3 have similar mononuclear structures, which are further linked into one‐dimensional (1D) supramolecular chains by various intermolecular weak interactions, such as C–H ··· F hydrogen‐bonding, and π ··· π stacking interactions. The results indicate that the steric bulk of L¹ and L² and the existence of hexafluoroacetylacetonate (hfac) play important roles in controlling the formation of the final frameworks of complexes 1 – 3 . Moreover, the luminescent properties of the ligands and their complexes were investigated in detail.     

Synthesis,Crystal Structures and Magnetic Properties of Copper(II) Complexes with Nitronyl Nitroxide Radicals

Two new copper(II) compounds with imino nitroxide radicals [Cu(IM‐MeImz)₂ · (SCN)] 0.5[Cu(SCN)₄] ( 1 ) and [Cu(IM‐MeImz)₂ · (SCN)]ClO₄ · H₂O ( 2 ) (IM‐meImz = 2‐(5‐methylimidazol‐4‐yl)‐4,4,5,5‐tetramethyl‐2‐imidazoline‐1‐oxyl) have been synthesized and characterized structurally and magnetically. X‐ray analysis demonstrates that complex 1 contains Cu^II ions in both square‐pyramidal and square planar coordination. There are complete charge separation into [Cu(IM‐MeImz)₂(SCN)]⁺ cations and 0.5[Cu(SCN)₄]^? anions, in a 2:1 ratio. The complex 1 was connected as a one‐dimensional polymer by intermolecular interactions. In complex 2 , the coordination around the copper atom is distorted square pyramidal and the apical position is occupied by one nitrogen atom of SCN^? anion. The 2‐D network structure was formed and arranged through intermolecular H‐bonds interactions. The complex 1 exhibits intramolecular weak ferromagnetic coupling between Cu^II ion and the radicals.     

Synthesis,Structure and Magnetic Properties of a Novel Nickel(II) Radical Heterospin Complex with Salicylaldoxime

A novel heterospin complex containing both Ni^II and nitroxide radical ligands: [Ni(salox)₂(NIT4Py)₂] ( 1 ) (salox = salicylaldoxime, NIT4Py = 2‐(4′‐pyridyl)‐4,4,5,5‐ tetramethyl‐imidazoline‐1‐oxyl‐3‐oxide) has been synthesized and structurally characterized. The structure consists of neutral Ni(salox)₂(NIT4Py)₂ moieties bridged by intermolecular hydrogen bonds, forming a one‐dimensional chain structure. Magnetic measurements show intramolecular antiferromagnetic interactions between NIT4Py and Ni²⁺ ion.     

Synthesis and Magnetic Properties of (Pyrrolidin‐1‐oxyl)–(Nitronyl Nitroxide)/(Iminonitroxide)‐Dyads

Unlike extensively studied diradicals linked by π‐conjugated systems, only a few studies have investigated weakly coupled diradicals linked by an sp³ carbon atom. Herein, we prepared pyrrolidin‐1‐oxyl–(nitronyl nitroxide)‐dyad 5 and pyrrolidin‐1‐oxyl–iminonitroxide‐dyad 6 . From the observed temperature dependence of the magnetic susceptibility, 5 and 6 were determined to be in singlet ground states with 2J_intra/k_B=?35.2 K and ?13.6 K, respectively. From these results and theoretical calculations of related diradicals, the spin‐polarization model counting the small spin density of the sp³ carbon atom could be used as a spin‐prediction model.     

Structure and Magnetic Investigation of a Series of Rare Earth Heterospin Monometallic Compounds of Nitronyl Nitroxide Radical

Five rare earth heterospin complexes [Ln(hfac)₃(NITptBuPh)₂], [Ln^III = Eu ( 1 ), Tb ( 2 ), Dy ( 3 ), Ho ( 4 ), Er ( 5 )] (hfac = hexafluoroacetylacetonate), were synthesized with the radical ligand NITptBuPh [2‐(4′‐tert‐butylphenyl)‐4, 4,5, 5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide]. These complexes exhibit similar structures. All of them crystallize in the monoclinic space group P2₁/c, and consist of discrete mononuclear molecules. The central Ln^III ion is eight‐coordinate with a distorted dodecahedral environment. The NITptBuPh radical acts as monodentate ligand towards Ln^III ion through the NO group. The magnetic studies suggested weak antiferromagnetic interactions between Ln^III ion and radicals in 1 , 3 , 4 , and 5 , but weak ferromagnetic interaction in 2 .     

Tetranuclear Complexes with {M4O4} (M = CoII,NiII) Cubane‐Like Core: Synthesis,Crystal Structure,and Magnetic Properties

Two tetranuclear clusters of formula [M₄L₄(HOMe)₄] {H₂L = (E)‐1‐[(2‐(hydroxymethyl)phenylimino)methyl]naphthalen‐2‐ol} [M = Co ( 1 ), Ni ( 2 )] were hydrothermally synthesized by reaction of M(OAc)₂ · 4H₂O with H₂L and NaOH in MeOH. X‐ray crystal structure analysis revealed that complexes 1 and 2 are isostructural. In the core of the structures, four M^II ions and four oxygen atoms occupied alternate vertices of [M₄O₄] cubane. The magnetic property measurements of 1 and 2 revealed that overall ferromagnetic M^II ··· M^II exchange interactions exist in both complexes.     

A Novel Ruthenium(III) and Lithium Complex: Synthesis,Crystal Structure,and Magnetic Properties

A novel complex [Li₃{μ‐(H₂O)₆}(H₂O)₆]·[RuCl₆] has been synthesized and was characterized by single‐crystal X‐ray diffraction. The compound crystallizes in rhombohedral space group R3¯c, with the unit cell parameters a = b = 9.948(2)Å, c = 33.376(14)Å, γ = 120°, V = 2860.5(15)ų, Z = 6, D_c = 1.918 Mg m^—3, μ = 1.703 mm^—1, R = 0.0244, wR = 0.0478. The compound consists of a cation, which contains three lithium ions linked by six bridged water molecules, and an anion, which contains a ruthenium(III) ion. The whole complex can be described as a three‐dimensional structure linked by hydrogen bonds between cation and anion. The magnetic properties of the complex have been investigated. The IR, UV‐vis and EPR spectra are studied.     

Syntheses,Crystal Structures,and Magnetic Properties of Two Mononuclear Nickel‐Nitronyl Nitroxide Radical Compounds

Two nickel(II) complexes were synthesized and structurally as well as magnetically characterized by using two positional isomeric nitronyl nitroxide radical ligands and H₃cda as co‐ligand: [Ni(NIToPy)(cda)]H₂O · CH₃OH ( 1 ) and [Ni(IM4Py)₂(cda)H₂O] ( 2 ) [NIToPy = 2‐(3′‐pyridinyl)‐4,4,5,5‐tetramethyl‐4,5‐dihydro‐1H‐imidazolyl‐1‐oxyl‐3‐oxide; IM4Py = 2‐(4′‐pyridinyl)‐4,4,5,5‐tetramethylimidazoline‐l‐oxyl; H₃cda = 4‐hydroxypyridine‐2,6‐dicarboxylic acid]. Single‐crystal structures analyses show that both complexes have similar mononuclear structures, in which the central Ni^II ions are hexacoordinated with a distorted octahedral arrangement. The magnetic properties of 1 and 2 were studied, and antiferromagnetic interactions between Ni^II ion and radicals are observed.     

Zinc(II) and Nickel(II) Complexes Based on Schiff Base Ligands: Synthesis,Crystal Structure,Luminescent and Magnetic Properties

Three new phenolate oxygen bridged transition metal complexes [Zn₃(HL¹)₃(μ₃‐CH₃O)]·(ClO₄)₂(H₂O)₃ ( 1 ), [Ni₂(HL¹)₂(μ_1,1‐N₃)(o‐vanillin)]·H₂O ( 2 ), [Ni₃(HL²)₂(PhCOO)₂(PhCOOH)₂(EtOH)₂] ( 3 ) have been synthesized by metal ions and potentially multidentate Schiff base ligands (H₂L¹ = 2‐((1‐hydroxy‐2‐methylpropan‐2‐ylimino) methyl)‐6‐methoxyphenol; H₃L² = (E)‐1‐((2‐hydroxy‐3‐methoxy‐benzylidene)amino)ethane‐1,2‐diol). All the three complexes 1 , 2 , and 3 have been characterized by elemental analysis, FT‐IR spectroscopy, and single‐crystal X‐ray diffraction studies. Crystal structures reveal that complex 1 is a trinuclear incomplete cubane‐like zinc cluster whereas complex 2 is a dinuclear nickel complex bridged by azide, and compound 3 is a trinuclear nickel complex. The luminescent property for complex 1 and magnetic behaviors for complexes 2 and 3 have been investigated.     

Synthesis,Characterization, and Magnetic Behaviour of Dinuclear Nickel(II) Complexes of N,N′‐Substituted Dithiooxamides derived from α‐Amino Acids

New dinuclear complexes of the types [Ni₂(L)(H₂O)₂] and [Ni₂(L)(H₂O)₆] [H₄L = N,N′‐bis(carboxymethyl) dithiooxamide (H₄GLYDTO), N,N′‐bis(1‐carboxyethyl) dithiooxamide (H₄ALADTO), N,N′‐bis(1‐carboxy‐2‐methylpropyl) dithiooxamide (H₄VALDTO) and N,N′‐bis(1‐carboxy‐3‐methylbutyl) dithiooxamide (H₄LEUDTO)] have been prepared and characterized by IR and electronic absorption spectroscopy, and the structure of [Ni₂(ALADTO)(H₂O)₆] crystals has been determined by single crystal X‐ray analysis. This compound is composed of discrete dinuclear units in which two Ni^II atoms with NO₄S kernels are linked by a single [ALADTO]^4– group that coordinates through its carboxylato oxygen, amino nitrogen and thiolato sulphur atoms. In each dimer unit the two nickel(II) ions in distorted octahedral coordination are separated by 5.863(2) Å The temperature dependence of the magnetic susceptibility of the new compounds was measured over the range 2 to 300 K. In the complexes of [GLYDTO]^4– and [ALADTO]^4– the two Ni atoms are antiferromagnetically coupled, with J = –23.51(4) and –20.95(8) cm^–1, respectively. By constrast, [Ni₂(VALDTO)(H₂O)₂], [Ni₂(VALDTO)(H₂O)₆] and [Ni₂(LEUDTO)(H₂O)₂] remain paramagnetic down to 2 K, with magnetic moment values between 2.8 and 3.3 M.B.     

Structure and Magnetic Property of a Novel Nitronyl Nitroxide Biradical

A new biradical of nitronyl nitroxide, 1,3‐[di‐2‐(4,4,5,5‐tetramethyl‐4,5‐dihydro‐1H‐imidazolyl‐1‐oxyl‐3‐oxide) phenoxy]propane [BNITPhOPr ( 1 )], was prepared and characterized. The temperature dependence of the magnetic susceptibility values were observed for 1 in the range of 2–300 K. The observed data was successfully simulated giving the exchange integral J = ?0.47 cm^?1, θ = ?0.94 K. This result indicates a weak antiferromagnetic spin exchange interaction between the biradicals.