A new nitronyl nitroxide radical L (L = 2-(4-(5-methyl-carbonyl-3-pyriyl)benzoxo)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) containing N–O groups and the pyridyl nitrogen group was designed and synthesized as a multidentate ligand to obtain compounds with interesting structures and magnetic properties from 3d or 3d-4f precursors. The reaction of Cu(hfac)2 and/or Gd(hfac)3·2H2O (hfac = hexafluoroacetylacetonate) with L resulted in a rare S = 13/2 high spin ground state CuII complex [(Cu(hfac)2)7(L)6] (1) and a CuII–GdIII chain complex [Gd(hfac)3Cu(hfac)2(L)2]n·0.5CH2Cl2 (2). Single crystal X-ray diffraction studies indicate that the N–O groups of the L radicals are all axially bound to CuII ions in complex 1, which result in the ferromagnetic exchange between CuII and radicals and an S = 13/2 high spin ground state. While adding Gd(hfac)3 units to the system of Cu(hfac)2 and L radical, a one dimension chain structure is obtained, and there are ferromagnetic GdIII-radical interactions and antiferromagnetic radical–radical coupling in the chain.

Three novel mononuclear lanthanide complexes coordinated with 1-methylimidazole [Ln(hfac)3·(1-MeIm)2] (Ln = Dy(1), Tb(2) and Ho(3), hfac = hexafluoroacetylacetonate, 1-MeIm = 1-methylimidazole) have been designed and characterized by single-crystal X-ray diffraction, luminescence and magnetic measurements. Studies indicate that the metal ions of all three mononuclear complexes adopt a slightly distorted D4d [LnO6N2] coordination environment, which is formed by two terminal 1-methylimidazole ligands and three bischelating hfac− anions. Frequency dependent out-of-phase signals were observed for complex 1 in dynamic magnetic susceptibility measurements, which indicates single-molecule magnetic behavior.

Three new lanthanide complexes [Ln(hfac)3(pz)2] (Ln = Dy (1), Tb (2), Ho (3); hfac = hexafluoroacetylacetonate; pz = pyrazole) based on pyrazole have been prepared and characterized structurally. X-ray crystallographic analysis reveals that all three complexes are isomorphous. The crystal structures of these complexes consist of a mononuclear molecule unit in which the center LnIII ion is surrounded with a slightly distorted D2d-dodecahedron LnO6N2 coordination sphere from three hfac anions and two pyrazole ligands. Both static and dynamic magnetic properties were studied for complex 1, which is proved to be a rarely reported D2d-symmetry DyIII mononuclear single-molecule magnet containing a monodentate N-heterocyclic donor ligand, and the luminescence characterization of complexes 1–3 in both visible and NIR regions is also studied.

Three new LnIII complexes based on 2,2′-bipyridine [Ln(hfac)3(bpy)] (Ln = Dy (1), Tb (2), or Ho (3); hfac = hexafluoroacetylacetonate; and bpy = 2,2′-bipyridine) have been synthesized and characterized structurally and magnetically. Single-crystal X-ray analysis shows that all these complexes contain one [Ln(hfac)3(bpy)] unit in which a center LnIII ion is surrounded with a slightly distorted square-antiprismatic LnO6N2 coordination sphere formed by three bischelate hfac anions and one bpy ligand. Both static and dynamic magnetic properties were studied for complex 1, which is proved to be a new single-ion magnet. The luminescence characterizations of complexes 1 and 2 are also studied in this paper.

Three heterospin complexes [M(NIT4Py)2(cda)H2O] (M = Cu(II) (1), Ni(II) (2), Co(II) (3)) with various paramagnetic 3d metal ions and pyridyl-substituted nitronyl nitroxide radical (NIT4Py = 2-(4′-pyridyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide, H2cda = 4-hydroxy-pyridine-2,6-dicarboxylic acid) have been synthesized, characterized structurally and magnetically. The single crystal structures show that complexes 1–3 are isomorphic, and have 2D supramolecular network consisting of [M(NIT4Py)2(cda)H2O] with three paramagnetic centers. The magnetic measurements indicated that complexes 1–3 exhibit all antiferromagnetic interactions between M(II) and radicals with JCu–rad = −7.30 cm−1, JNi–rad = −3.58 cm−1 and JCo–rad = −1.85 cm−1, respectively. Their magnetic behaviors were interpreted in terms of the spin polarization mechanism of the π-electrons of NIT4Py and the orthogonality of 3d magnetic orbital of M(II) ion and the 2pπ orbital on the pyridine rings of NIT4Py.Graphical abstractThree heterospin complexes with paramagnetic 3d metal ions (Cu(II), Co(II), Ni(II)) and pyridyl-substituted nitronyl nitroxide radical have been synthesized and structurally characterized. The magnetic behaviors of the three complexes exhibit all antiferromagnetic M(II)–radical interactions. And the magnetic properties were studied based on the orthogonality of orbitals and spin polarization mechanism of radical.Highlights► Three 3d metal–radical heterospin complexes were successfully synthesized. ► Complexes 1–3 are described as 2D supramolecular network with 3d paramagnetic centers. ► The magnetic measurements indicated that complexes 1–3 exhibit all antiferromagnetic interactions between 3d metal and radicals.

Four new copper(II) complexes containing different nitronyl nitroxide radicals have been synthesized, characterized structurally and magnetically: [(Cu(hfac)2)3(NITPh-3-Br-4-OMe)2] (1), [(Cu(hfac)2)3(NITPyOMe)2] (2), [Cu(hfac)2(2-QNNN)] (3) and [Cu(hfac)2(NITmNO2)2] (4) (hfac = hexafluoro-acetylacetonate; and NITPh-3-Br-4-OMe = 2-3′-Br-4′-methoxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, NITPyOMe = 2-4′-methoxy-3′-pyridyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide, 2-QNNN = 2-2′-quinolyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, NITmNO2 = 2-(3-nitrophenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide). The X-ray crystal structure analyses show that complexes 1 and 2 have similar centrosymmetric five-spin structures built by three Cu(hfac)2 units bridged by two nitroxide ligands through their NO groups. While complex 3 consists of isolated molecule where the nitronyl nitroxide radical acts as chelating ligand towards copper(II), and complex 4 is a rare mononuclear tri-spin compound, in which central Cu(II) ion is coordinated by two hfac and two NITmNO2 radicals. The variable-temperature magnetic susceptibility studies reveal strong antiferromagnetic interactions between Cu(II) ions and radicals in complexes 1–2, practically diamagnetic in complex 3 and weak ferromagnetic interaction in complex 4.Four novel Cu(hfac)2 complexes based on different nitronyl-nitroxide radicals have been synthesized, and steric hinderance greatly affects the structure of complexes.

A new cyano-bridged TbIII–CrIII heterometallic complex [Tb(H2O)2(DMF)4{Cr(CN)6}]·H2O (DMF = dimethylformamide) (1), assembled from paramagnetic hexacyanochromium(III) [Cr(CN)6]3− building block and highly anisotropic terbium(III) ion has been prepared and structurally and magnetically characterized. Complex 1 shows one-dimensional (1D) zig-zag chain-like structural motif which is further extended into three-dimensional network through hydrogen-bonding interactions. The long-range magnetic ordering observed in complex 1, which is possibly due to interchain magnetic dipolar interactions, illuminates that this complex is a molecule-based magnet with critical temperature of about 5 K. This higher critical temperature among those of LnIII–CrIII heterometallic complexes exhibiting long-range magnetic ordering is probably due to the introduction of highly anisotropic terbium(III) ion.

Seven Ln(III) complexes based on a novel nitronyl nitroxide radical have been synthesized and characterized structurally and magnetically: [Ln(hfac)3(NITNapOMe)2] (Ln = Pr(1), Gd(2), Tb(3), Dy(4), Ho(5), Er(6), Tm(7); hfac = hexafluoroacetylacetonate; NITNapOMe = 2-6′-methoxy-2′-naphthyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide). The single-crystal analyses show that these complexes have similar mononuclear tri-spin structures, in which central Ln(III) ions are eight coordinated by three hfac molecules and two NITNapOMe radicals. The variable-temperature magnetic susceptibility studies reveal the ferromagnetic interactions between Ln(III) ion and radicals in complexes 3, 4, and 7 and antiferromagnetic interactions in complexes 1, 2, 5, and 6.

Four Ln(III) complexes based on two nitronyl nitroxide radicals with different steric hindrance have been synthesized, characterized structurally and magnetically: [Ln(hfac)3(NITPhOEt)]n (Ce (1), Pr (2); hfac = hexafluoroacetylacetonate; and NITPhOEt = 4′-ethoxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide); [Ln(hfac)3(NITPhOCH2Ph)2] (Ce (3), Pr (4); NITPhOCH2Ph = 4′-benzyloxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide). The X-ray crystal structure analyses show that small steric hindrance of the radical makes complexes 1 and 2 show similar linear chain structures composed of Ln(hfac)3 units bridged by NITPhOEt radicals through their N–O groups. While the larger steric hindrance of the radical induces complexes 3 and 4 to be mononuclear tri-spin compounds, in which central Ln(III) ions are coordinated by three hfac and two NITPhOCH2Ph radicals. The variable-temperature magnetic susceptibility studies reveal that there are antiferromagnetic interactions between the paramagenetic ions (Ln(III) and radical) in all four complexes.

The reaction of [Mo(CN)8]3− with Dy3+ in DMF solvent leads to a new binuclear complex, [Mo(CN)8Dy(DMF)4(H2O)3]·H2O (1) (DMF = N,N′-dimethylformamide). Magnetic measurements confirm that 1 presents probably a ferromagnetic interaction between the binuclear complexes.Construct a binuclear MoV–DyIII complex, in which the coordination sphere of Dy and Mo atoms lie in a slightly distorted trigonal dodecahedron geometry and linked by cyanide group.Research Highlights► Magnetic analysis. ► The magnetic anisotropy of DyIII ion. ► The progressive depopulation of excited Stark sublevels of DyIII ion.

Three Radical–Ln(III)–Radical complexes based on nitronyl nitroxide radicals have been synthesized, structurally and magnetically characterized: [Gd(hfac)3(NITPhOEt)2] (1) (hfac=hexafluoroacetylacetonate, and NITPhOEt=4′-ethoxy-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), [Gd(hfac)3(NITPhOCH2Ph)2] (2) (NITPhOCH2Ph=4′-benzyloxy-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) and [Lu(hfac)3(NITPhOCH2Ph)2] (3). The X-ray crystal structure analyses show that the structures of the three compounds are similar and all consist of the isolated molecules, in which central ions GdIII or LuIII are coordinated by six oxygen atoms from three hfac and two oxygen atoms from nitronyl radicals. The magnetic studies show that in both of the two GdIII complexes, there are ferromagnetic GdIII–Rad interactions and antiferro-magnetic Rad–Rad interactions in the molecules (with JRad−Gd=0.27 cm−1, jRad–Rad=−2.97 cm−1 for 1: and JRad−Gd=0.62 cm−1, jRad–Rad=−7.01 cm−1 for 2). An analogous complex of [Lu(hfac)3 (NITPhOCH2Ph)2] (3) containing diamagnetic LuIII ions has also been introduced for further demonstrating the nature of magnetic coupling between radicals.Two tri-spin complexes based on gadolinium-radical have been synthesized and characterized, the magnetic studies show that in the two complexes the Gd–radical interaction is ferromagnetic and the radical–radical interaction is antiferromagnetic. An analogous complex containing the diamagnetic LuIII ions has also been synthesized to further demonstrate the nature of the magnetic coupling between radicals.

A new cyano-bridged TbIII–CrIII heterometallic complex [Tb(H2O)2(DMF)4{Cr(CN)6}]·H2O (DMF = dimethylformamide) (1), assembled from paramagnetic hexacyanochromium(III) [Cr(CN)6]3− building block and highly anisotropic terbium(III) ion has been prepared and structurally and magnetically characterized. Complex 1 shows one-dimensional (1D) zig-zag chain-like structural motif which is further extended into three-dimensional network through hydrogen-bonding interactions. The long-range magnetic ordering observed in complex 1, which is possibly due to interchain magnetic dipolar interactions, illuminates that this complex is a molecule-based magnet with critical temperature of about 5 K. This higher critical temperature among those of LnIII–CrIII heterometallic complexes exhibiting long-range magnetic ordering is probably due to the introduction of highly anisotropic terbium(III) ion.