Hybrid Spin-Crossover Conductor Exhibiting Unusual Variable-Temperature Electrical Conductivity

We describe the multistep synthesis of a new terthienyl-substituted QsalH ligand and an iron(3+) spin-crossover complex (1) containing this ligand, which electropolymerizes to produce a hybrid-conducting metallopolymer film (poly1). Variable-temperature magnetic susceptibility measurements demonstrate that spin-crossover is operative in the polymer film, and resistivity measurements on indium−tin oxide coated glass slides containing the polymer film exhibit intriguing temperature-dependent profiles

Synthesis of Multitopic Verdazyl Radical Ligands. Paramagnetic Supramolecular Synthons

The syntheses of several verdazyl radical and diradicals containing pyridine-based multitopic coordination sites are described. These compounds were designed to be paramagnetic analogues of oligopyridine metallosupramolecular building blocks

Polynuclear Cu₄L₄ Copper(II) Aminyl Radical Coordination Complexes

We describe the structural features and magnetic properties of two polynuclear copper­(II) complexes containing a redox-active ligand. These neutral complexes each bear the formula RL₄Cu₄ (R = ^tBu, Me) with the ligand in a dianion-aminyl radical oxidation state. X-ray data and density functional theory calculations support an aminyl-type radical character in these complexes, making these the first polynuclear metal aminyl radical complexes

Synthesis, Structure, and Magnetism of Bimetallic Manganese or Nickel Complexes of a Bridging Verdazyl Radical

Two binuclear metal−radical complexes, formed by the reaction of M(hfac)2·2H2O (M = Mn or Ni; hfac = hexafluoroacetylacetonate) with the 1,5-dimethyl-3-(4,6-dimethylpyrimidin-2-yl)-6-oxoverdazyl radical (3), were synthesized. The binuclear Mn complex 5 (i.e., 3[Mn(hfac)2]2) crystallizes in the monoclinic space group C2/c:  C30H17N6O9F24Mn2, a = 29.947(3), b = 17.143(3), c = 16.276(3) Å, β = 123.748(3)°, Z = 4. The compound consists of two pseudo-octahedral Mn(II) ions, both bearing two hfac ancillary ligands, bridged by the bis(bidentate) radical 3. The temperature dependence of the magnetic susceptibility of 5 reveals moderate antiferromagnetic exchange between each of the Mn(II) ions and the verdazyl radical (J = −48 cm-1). The S = 9/2 ground spin state of the complex was corroborated by low-temperature magnetization versus field measurements. In contrast, the magnetic susceptibility versus temperature behavior of 6 (whose molecular structure is presumed to be analogous to that of 5) indicates that the two Ni(II) ions are strongly ferromagnetically coupled to the verdazyl radical (J = +220 cm-1). The magnetization versus field behavior of 5 is consistent with an S = 5/2 ground-state species

Verdazyl Radicals as Oligopyridine Mimics: Structures and Magnetic Properties of M(II) Complexes of 1,5-Dimethyl-3-(2,2‘-bipyridin-6-yl)-6-oxoverdazyl (M = Mn, Ni, Cu, Zn)

The verdazyl radical 1,5-dimethyl-3-(2,2‘-bipyridin-6-yl)-6-oxoverdazyl (3) was prepared, and its homoleptic metal complexes M(3)22+·2X- (5, M = Mn(II); 6, M = Ni(II); 7, M = Cu(II); 8, M = Zn(II); X = ClO4, PF6) were characterized by single-crystal X-ray diffraction and variable-temperature magnetic susceptibility measurements. Relevant crystallographic parameters are as follows:  5, monoclinic space group Pna21, a = 18.755(4) Å, b = 11.154(3) Å, c = 16.594(4) Å, α = 90.00°, β = 90.00°, γ = 90.00°, V = 3471.4(13) Å3, and Z = 4; 7, triclinic space group P1̋, a = 9.4638(18) Å, b = 9.8442(19) Å, c = 18.769(4) Å, α = 103.746(3)°, β = 92.925(3)°, γ = 94.869(3)°, V = 1687.8(6) Å3, and Z = 2; 8, triclinic space group P1̋, a = 9.4858(14) Å, b = 9.7919(14) Å, c = 18.889(3) Å, α = 104.196(3)°, β = 92.855(3)°, γ = 94.216(3)°, V = 1692.1(4) Å3, and Z = 2. In all cases, the two verdazyl-based ligands bind almost perpendicular to each other in meridional positions, yielding pseudooctahedral metal complexes whose general structural features are strongly reminiscent of metal bis(terpyridine) complexes. The intramolecular metal−verdazyl magnetic exchange coupling is strongly ferromagnetic in 6 (JNi-vd= +240 cm-1), and strongly antiferromagnetic in 5 (JMn-vd= −93 cm-1). Complex 7 exhibits weak ferromagnetic coupling (JCu-vd = −4.5 cm-1). Intramolecular radical−radical coupling in the zinc complex 8 was found to be weakly antiferromagnetic (Jvd-vd = −8 cm-1). Intramolecular radical−radical exchange was generally weak in the four metal complexes, ranging from −10 cm-1 (for 5) to +2 cm-1 (for 7). The low-temperature magnetic behavior of 7 and 8 is complex, possibly arising from a combination of intra- and intermolecular interactions

Molecular and Electronic Structures of Complexes Containing 1‑(2-pyridylazo)-2-phenanthrol (PAPL): Revisiting a Redox-Active Ligand

Herein we report the molecular structures and electronic properties of neutral, homoleptic, six-coordinate complexes of the general formula M­(PAPL)₂, where PAPL is the monoanion of 1-(2-pyridylazo)-2-phenanthrol (M = Mn, Ni, Zn). Although, the coordination chemistry of PAPL has been investigated in a few previous reports in the 1970s and 1980s, there are, to our knowledge, no reported single crystal X-ray diffraction studies of any complexes, or any other electronic property or computational studies of complexes containing the PAPL anion until now. The electronic structures of the complexes are probed with a combination of cyclic voltammetry, UV–vis spectroscopy, and spectroelectrochemical measurements. Density functional theory calculations support the redox-active nature of the PAPL ligand. In all complexes we observe two reversible ligand-centered reduction processes, suggesting it may be possible to access the open-shell radical-anionic state of the ligand

Molecular and Electronic Structures of Complexes Containing 1‑(2-pyridylazo)-2-phenanthrol (PAPL): Revisiting a Redox-Active Ligand

Herein we report the molecular structures and electronic properties of neutral, homoleptic, six-coordinate complexes of the general formula M­(PAPL)₂, where PAPL is the monoanion of 1-(2-pyridylazo)-2-phenanthrol (M = Mn, Ni, Zn). Although, the coordination chemistry of PAPL has been investigated in a few previous reports in the 1970s and 1980s, there are, to our knowledge, no reported single crystal X-ray diffraction studies of any complexes, or any other electronic property or computational studies of complexes containing the PAPL anion until now. The electronic structures of the complexes are probed with a combination of cyclic voltammetry, UV–vis spectroscopy, and spectroelectrochemical measurements. Density functional theory calculations support the redox-active nature of the PAPL ligand. In all complexes we observe two reversible ligand-centered reduction processes, suggesting it may be possible to access the open-shell radical-anionic state of the ligand

π-Extended and Six-Coordinate Iron(II) Complexes: Structures, Magnetic Properties, and the Electrochemical Synthesis of a Conducting Iron(II) Metallopolymer

Herein, we describe the preparation of three new bidentate π-extended derivatives of the ligand N-phenyl-2-pyridinalimine (ppi) containing a 3-thienyl (4) substituent at position 4 of the aniline ring or 2-thienyl (6) or phenyl (2) substituents at each of the 2,5 positions of the aniline rings. Three iron(2+) complexes (7–9) containing these ligands were prepared by combining two equivalents each of 2, 4, or 6 with Fe(NCS)2, and the resulting neutral, six-coordinate complexes were fully characterized, including with single crystal X-ray diffraction experiments in the case of complexes 7 and 9. Variable temperature magnetic susceptibility and Mössbauer experiments confirm the presence of spin-crossover in complexes 7 and 8, and the unusual solid state variable temperature magnetic properties of complex 9 likely result from crystal packing forces. Electropolymerization of the 2,5-dithienyl-substituted complex (9) produces a conducting and electrochromic metallopolymer film (poly-9)

Weak Magnetic Coupling of Coordinated Verdazyl Radicals through Diamagnetic Metal Ions. Synthesis, Structure, and Magnetism of a Homoleptic Copper(I) Complex

Weak Magnetic Coupling of Coordinated Verdazyl Radicals through Diamagnetic Metal Ions. Synthesis, Structure, and Magnetism of a Homoleptic Copper(I) Comple

Synthesis, Structure, and Magnetism of Bimetallic Manganese or Nickel Complexes of a Bridging Verdazyl Radical

Two binuclear metal−radical complexes, formed by the reaction of M(hfac)2·2H2O (M = Mn or Ni; hfac = hexafluoroacetylacetonate) with the 1,5-dimethyl-3-(4,6-dimethylpyrimidin-2-yl)-6-oxoverdazyl radical (3), were synthesized. The binuclear Mn complex 5 (i.e., 3[Mn(hfac)2]2) crystallizes in the monoclinic space group C2/c:  C30H17N6O9F24Mn2, a = 29.947(3), b = 17.143(3), c = 16.276(3) Å, β = 123.748(3)°, Z = 4. The compound consists of two pseudo-octahedral Mn(II) ions, both bearing two hfac ancillary ligands, bridged by the bis(bidentate) radical 3. The temperature dependence of the magnetic susceptibility of 5 reveals moderate antiferromagnetic exchange between each of the Mn(II) ions and the verdazyl radical (J = −48 cm-1). The S = 9/2 ground spin state of the complex was corroborated by low-temperature magnetization versus field measurements. In contrast, the magnetic susceptibility versus temperature behavior of 6 (whose molecular structure is presumed to be analogous to that of 5) indicates that the two Ni(II) ions are strongly ferromagnetically coupled to the verdazyl radical (J = +220 cm-1). The magnetization versus field behavior of 5 is consistent with an S = 5/2 ground-state species