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.     

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.     

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.     

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 .     

Syntheses, crystal structures, magnetic properties of two new lanthanide-nitronyl nitroxide complexes (Ln = Gd, Nd)

Two new complexes based on lanthanide ions and nitronyl nitroxide radical, Ln(hfac)₃(NITPh-p-Cl)₂ (Ln = Gd(1), Nd(2); hfac = hexafluoroacetylacetonate; NITPh-p-Cl = 2-(4′-chlorphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) have been synthesized and characterized by single-crystal X-ray diffraction. The single-crystal structures show that two complexes have similar structures, which consist of radical-Ln-radical isolated molecules. The Ln(III) ions are eight-coordinated in slightly distorted dodecahedral geometry. NITPh-p-Cl molecules act as monodentate ligands linking two Ln(III) ions through the oxygen atoms of the N-O groups. The magnetic studies show that the spin coupling between the Gd(III) ion and the radicals in the complex 1 is weak ferromagnetic (J = 0.38 cm⁻¹), while complex 2 exhibits antiferromagnetic interactions (zJ′ = −0.36 cm⁻¹) between Nd(III) ion 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.     

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,Crystal Structure and Magnetic Properties of Zinc (II) Chloride Complexes with Pyridyl‐Substituted Nitronyl Nitroxides

ZnCl₂(NIT‐pPy) 1 , (NIT‐pPy = 2‐(4‐pyridyl)‐4,4,5,5‐tetramethyl‐4,5‐dihydro‐1H‐imidazolyl‐1‐oxyl‐3‐oxide) crystallizes in the orthorhombic space group Pnn2 with the cell parameters a = 9.4083(9), b = 39.686(3), c = 7.4417(14) Å. ZnCl₂(NIT‐6M‐oPy) 2 , (NIT‐6M‐oPy = 2‐(6‐methyl‐2‐pyridyl)‐4,4,5,5‐tetramethyl‐4,5‐dihydro‐1H‐imidazolyl‐1‐oxyl‐3‐oxide) crystallizes in the monoclinic space group Pn with a = 7.377(2), b = 19.096(4), c = 11.853(2) Å, β = 95.65(3)°. The temperature dependence magnetic susceptibility of complex 1 revealed an intermolecular ferromagnetic exchange interaction. A simple spin‐polarization model has been used to justify the observed ferromagnetic exchange interaction between the spins of the radical NO group in complex 2 .     

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.     

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.     

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.     

Syntheses,Crystal Structures,and Magnetic Properties of Three 1D Chain Metal–Nitroxide Complexes Bridged by ­Flexible Dicarboxylate Anions

Three new one‐dimensional (1D) chain metal–nitroxide complexes {[Cu(NIT4Py)₂(suc)(H₂O)] · 3H₂O}_n ( 1 ), {[Cd(NIT4Py)₂(suc)(H₂O)] · [Cd(NIT4Py)₂(suc)(H₂O)₂] · 3H₂O}_n ( 2 ), and {[Zn(NIT4Py)(glu)(H₂O)] · H₂O}_n ( 3 ) [NIT4Py = 2‐(4′‐pyridyl)‐4, 4, 5, 5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide, suc = succinate anion and glu = glutarate anion] were synthesized and structurally characterized. Single‐crystal X‐ray analyses indicate that the three complexes crystallize in neutral 1D chains in which the metal‐nitroxide units are linked by flexible dicarboxylate anions. The succinate anions only adopt trans configuration in complexes 1 and 2 , whereas the glutarate anion has gauche/anti conformation in complex 3 . Magnetic measurements show that complex 1 exhibits weak antiferromagnetic interactions between the copper ions and the nitroxides.     

Two Isostructural Layered Lanthanide(III) Complexes: Syntheses,Structures, Magnetic and Luminescent Properties

Two N'-(2-hydroxybenzylidene)pyridine N-oxide-carbohydrazide (H₃L)-based coordination complexes with the formula [Ln₂(DMF)₂(OAc)₂(HL)₂]_n (Ln = Dy for 1 and Eu for 2 ) were solvothermally synthesized. Crystal structures, thermal stabilities, magnetic and luminescent properties of the two complexes were fully investigated. Both complexes are isomorphic two-dimensional layers with centrosymmetric {Ln₂} subunits extended by doubly deprotonated HL^2– connectors. Complex 1 with highly anisotropic Dy^III spin exhibits slightly frequency-dependent magnetic relaxations under zero dc field with an effective energy barrier of ca. 6.84 K. Eu^III-based complex 2 displays only one weak fluorescent emission around 532 nm with the absence of characteristic emission of Eu^III ion. These results provide helpful hints of the hydrazide Schiff-functionalized organic ligands on the function modulations of the resulting Ln complexes.     

Triphenylamine Derivatives Containing Nitronyl Nitroxide and Iminyl Nitroxide‐Syntheses,Characterization, Crystal Structures and Magnetic Studies

New triphenylamine derivatives 1, 2, 3, and 4 were synthesized and characterized by IR, FAB‐MS, EPR and EA. All of them displayed similar absorption and fluorescence spectra except compound 1, for which a possible explanation was proposed. Quasi‐reversible oxidation waves at about 0.76 V (vs. SCE) and 1.1 V for nitronyl nitroxide and iminyl nitroxide respectively as well as irreversible one at about 1.5 V for triphenylamine group were detected with cyclic voltammetry for compounds 1, 2, 3 and 4. Crystal structures of 2 and 4 were determined by X‐ray diffraction analysis. Their crystal data are as follows: for 2: monoclinic, C2/c, a = 1.69914 (4), b = 1.37435(5), c = 1.24621(5) ran, β= 106.553(2)°, V = 2.7896(2) nm³ Z = 4; for 4: orthorhombic, Pbca, a = 1.95970(6), b = 1.33096(4), c = 4.84691(14) nm, V = 12.6421(7) nm³, Z = 8. Magnetic studies indicated that all of them showed antiferromagnetic properties in solid state, but with strong intermolecular spin‐spin coupling as indicated by the relatively large values of 6, in particular for 4 (θ = ?12 K). Possible spin‐spin interaction mechanism was suggested based on the crystal structures of 2 and 4.     

两个氮氧自由基的合成与晶体结构：双自由基与阳离子自由基

合成并表征了2个氮氧自由基：2,2′-(2,5-二甲基苯基)-1,4-双(4,4,5,5-四甲基咪唑啉-3-氧化-1-氧基)自由基1和水合碘化m-N,N′,N″-三甲基苯铵基)-4,4,5,5-四甲基咪唑啉-3-氧化-1-氧基自由基2。双自由基1和阳离子自由基2均结晶于单斜晶系,P2₁/c空间群。通过分子间的氢键作用,2个化合物形成三维超分子体系。     

两个双核稀土-自由基化合物的合成、结构及磁性

以乙酰丙酮为共配体的稀土配合物与2-羟基苯取代的自由基配体进行反应得到2个新颖的稀土-自由基配合物[Ln₂（acac）₄（NIT-PhO）₂]（Ln=Tb（1）,Y（2）;acac=乙酰丙酮,NIT-PhOH=2-（2''-hydroxyphenyl）-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide）。2个配合物的结构相同,均是通过2个自由基配体上的羟基氧原子桥联2个稀土离子构成双核结构。直流磁化率的研究表明配合物2具有弱的反铁磁性质。     

Three Phenoxo‐Bridged Dinuclear Lanthanide Complexes: Syntheses,Crystal Structures,and Magnetic Properties

Three dinuclear lanthanide complexes [Ln₂(H₂L)₂(NO₃)₄] [Ln = Dy ( 1 ), Tb ( 2 ), and Gd ( 3 )] [H₃L = 2‐hydroxyimino‐N′‐[(2‐hydroxy‐3‐methoxyphenyl)methylidene]‐propanohydrazone] were solvothermally synthesized by varying differently anisotropic rare earth ions. Single‐crystal structural analyses demonstrate that all the three complexes are crystallographically isostructural with two centrosymmetric Ln^III ions aggregated by a pair of monodeprotonated H₂L^– anions. Weak intramolecular antiferromagnetic interactions with different strength were mediated by a pair of phenoxo bridges due to superexchange and/or single‐ion anisotropy. Additionally, the Dy^III‐based entity shows the strongest anisotropy exhibits field‐induced single‐molecule magnetic behavior with two thermally activated relaxation processes. In contrast, 3 with isotropic Gd^III ion has a significant cryogenic magnetocaloric effect with the maximum entropy change of 25.7 J · kg^–1 · K^–1 at 2.0 K and 70.0 kOe.     

Synthesis,Crystal Structure and Magnetic Behaviour of Two 1‐D Chain Manganese‐Nitroxide Complexes Bridged by Isophthalate Anions

Two one‐dimensional (1‐D) chain manganese‐nitroxide complexes {[Mn(NIT4Py)₂(ip)(H₂O)₂]·4H₂O}_n ( 1 ) and [Mn(IM4Py)₂(ip)(H₂O)₂]_n ( 2 ) (NIT4Py = 2‐(4′‐pyridinyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide, IM4Py = 2‐(4′‐pyridinyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl and ip = isophthalate anion) have been synthesized and characterized by elemental analyses, IR spectrum and electronic absorption spectra. Complex 1 was structurally characterized and it crystallizes in neutral 1‐D chains where Mn^II nitroxide units [Mn(NIT4Py)₂(H₂O)₂] are linked by isophthalate anions. The magnetic measurements show that complex 1 exhibits antiferromagnetic couplings, while complex 2 exhibits ferromagnetic interactions between the Mn^II ion and the nitroxide radicals.     

Three New Lanthanide Coordination Polymers Built from H2bpdc Ligands: Syntheses,Structures, and Properties

Three new lanthanide‐organic coordination polymers, {[Ln₂(bpdc)₂(H₂O)₆(NO₃)] · NO₃} [Ln = La ( 1 ), Ce ( 2 ), Pr ( 3 )] (H₂bpdc = 2, 2′‐bipyridine‐6, 6′‐dicarboxylic acid) were synthesized under hydrothermal conditions and structurally characterized by elemental analysis, IR spectroscopy as well as single‐crystal and powder X‐ray diffraction. Single‐crystal X‐ray diffraction analysis revealed that compounds 1 – 3 are isostructural, composed of two dimensional honeycomb network linked by bpdc ligands. The magnetic property of compound 3 was investigated.     

三个镧系金属氮氧自由基配合物的合成、结构及磁性

以氮氧自由基为配体,合成了3例氮氧自由基-稀土三自旋单核配合物[Ln（hfac）₃（NIT-Ph-4-Br）₂]（Ln=Gd（1）,Tb（2）,Dy（3）,hfac=六氟乙酰丙酮,NIT-Ph-4-Br=4,4,5,5-四甲基-2-（4''-溴）-咪唑啉-3-氧化-1-氧基自由基。单晶结构分析表明3个配合物均属单斜晶系P2₁/c空间群,配合物中的Ln（Ⅲ）离子为八配位模式,并且拥有相似的自由基-稀土-自由基单核结构。对配合物的磁性测试结果表明,配合物1中自由基与Gd（Ⅲ）离子之间存在着铁磁相互作用,自由基与自由基之间存在着反铁磁相互作用;配合物2,3中,稀土离子与自由基之间存在弱的反铁磁相互作用。