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

A Highly Electron-Deficient Analogue of Aniline, Soluble Oligomers, and Their Redox Properties

The synthesis and electrochemical oxidative coupling of a highly electron-deficient analogue of aniline results in the formation of soluble electron-deficient oligomers. Oligomers undergo related oxidation and reduction processes that are separated by a wide potential range. The mechanism behind this behavior is examined by cyclic voltammetry, optical absorption spectroscopy, 1H NMR spectroscopy, and density functional theory calculations. Mesomeric isomerization of the oxidized oligomers leads to a very stable oxidized state that requires a large (2.8 V) overpotential to return to the neutral form

A Highly Electron-Deficient Analogue of Aniline, Soluble Oligomers, and Their Redox Properties

The synthesis and electrochemical oxidative coupling of a highly electron-deficient analogue of aniline results in the formation of soluble electron-deficient oligomers. Oligomers undergo related oxidation and reduction processes that are separated by a wide potential range. The mechanism behind this behavior is examined by cyclic voltammetry, optical absorption spectroscopy, ¹H NMR spectroscopy, and density functional theory calculations. Mesomeric isomerization of the oxidized oligomers leads to a very stable oxidized state that requires a large (2.8 V) overpotential to return to the neutral form

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)

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)

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)

A Novel Bis Tridentate Bipyridine Carboxamide Ligand and Its Complexation to Copper(II): Synthesis, Structure, and Magnetism

A new bis tridentate ligand 2,2‘-bipyridine-3,3‘-[2-pyridinecarboxamide] H2L1 which can bind transition metal ions has been synthesized via the condensation of 3,3‘-diamino-2,2‘-bipyridine together with 2-pyridine carbonyl chloride. Two copper(II) coordination compounds have been prepared and characterized:  [Cu2(L1)(hfac)2]·3CH3CN·H2O (1) and [Cu2(L1)Cl2]·CH3CN (2). The single-crystal X-ray structures reveal that complex 1 crystallizes in the triclinic space group P1̄, with the unit cell parameters a = 12.7185(6) Å, b = 17.3792(9) Å, c = 19.4696(8) Å, α = 110.827(2)°, β = 99.890(3)°, γ = 97.966(3)°, V = 3868.3(3) Å3, Z = 4, R = 0.0321 and Rw = 0.0826. Complex 2 crystallizes in the monoclinic space group P21/n with the unit cell parameters a = 12.8622(12) Å, b = 9.6100(10) Å, c = 19.897(2) Å, β = 102.027(3)°, V = 2405.3(4) Å3, Z = 4, R = 0.0409 and Rw = 0.1005. In both complexes the ligand is in the dianionic form and coordinates the divalent CuII ions via one amido and two pyridine nitrogen donor atoms. In 1, the coordination geometry around both CuII ions is best described as distorted trigonal bipyramidal where the remaining two coordination sites are satisfied by hexafluoroacetylacetonate counterions. In 2 both CuII ions adopt a (4 + 1) distorted square pyramidal geometry. One copper forms a longer apical bond to an adjacent carbonyl oxygen atom, whereas the second copper is chelated to a neighboring Cu−Cl chloride ion to afford a μ-Cl-bridged dimerized [Cu2(L1)Cl2]2 complex. The magnetic susceptibility data for 1 (2 −270 K), reveal the occurrence of weak antiferromagnetic interactions between the CuII ions. In contrast, variable-temperature magnetic susceptibility measurements for 2 reveal more complex magnetic properties, with the presence of a weak antiferromagnetic exchange (J = −10.1 K) between the copper ions in each dinuclear copper complex and a stronger ferromagnetic exchange interaction (J = 32.9 K) between the CuII ions of the Cu(μ-Cl)2Cu dimeric bridging units

A Novel Bis Tridentate Bipyridine Carboxamide Ligand and Its Complexation to Copper(II): Synthesis, Structure, and Magnetism

A new bis tridentate ligand 2,2‘-bipyridine-3,3‘-[2-pyridinecarboxamide] H2L1 which can bind transition metal ions has been synthesized via the condensation of 3,3‘-diamino-2,2‘-bipyridine together with 2-pyridine carbonyl chloride. Two copper(II) coordination compounds have been prepared and characterized:  [Cu2(L1)(hfac)2]·3CH3CN·H2O (1) and [Cu2(L1)Cl2]·CH3CN (2). The single-crystal X-ray structures reveal that complex 1 crystallizes in the triclinic space group P1̄, with the unit cell parameters a = 12.7185(6) Å, b = 17.3792(9) Å, c = 19.4696(8) Å, α = 110.827(2)°, β = 99.890(3)°, γ = 97.966(3)°, V = 3868.3(3) Å3, Z = 4, R = 0.0321 and Rw = 0.0826. Complex 2 crystallizes in the monoclinic space group P21/n with the unit cell parameters a = 12.8622(12) Å, b = 9.6100(10) Å, c = 19.897(2) Å, β = 102.027(3)°, V = 2405.3(4) Å3, Z = 4, R = 0.0409 and Rw = 0.1005. In both complexes the ligand is in the dianionic form and coordinates the divalent CuII ions via one amido and two pyridine nitrogen donor atoms. In 1, the coordination geometry around both CuII ions is best described as distorted trigonal bipyramidal where the remaining two coordination sites are satisfied by hexafluoroacetylacetonate counterions. In 2 both CuII ions adopt a (4 + 1) distorted square pyramidal geometry. One copper forms a longer apical bond to an adjacent carbonyl oxygen atom, whereas the second copper is chelated to a neighboring Cu−Cl chloride ion to afford a μ-Cl-bridged dimerized [Cu2(L1)Cl2]2 complex. The magnetic susceptibility data for 1 (2 −270 K), reveal the occurrence of weak antiferromagnetic interactions between the CuII ions. In contrast, variable-temperature magnetic susceptibility measurements for 2 reveal more complex magnetic properties, with the presence of a weak antiferromagnetic exchange (J = −10.1 K) between the copper ions in each dinuclear copper complex and a stronger ferromagnetic exchange interaction (J = 32.9 K) between the CuII ions of the Cu(μ-Cl)2Cu dimeric bridging units

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)

Bimetallic Iron(3+) Spin-Crossover Complexes Containing a 2,2′-Bithienyl Bridging bis-QsalH Ligand

We describe the synthesis of a new 3,3′-diethynyl-2,2′-bithienyl bridging bis-QsalH ligand (5), and the preparation of four bimetallic iron(3+) complexes containing 5 with Cl− (6), SCN− (7), PF6− (8), and ClO4− (9) counteranions. We show with variable temperature magnetic susceptibility, Mössbauer, and electron paramagnetic resonance (EPR) spectroscopy that each complex undergoes a spin-crossover in the solid state. In all four complexes, we observe very gradual and incomplete S = 5/2, 5/2 to S = 1/2, 1/2 spin-crossover processes, with three of the four complexes exhibiting nearly identical magnetic properties. We investigated the electronic properties of the complexes by cyclic and differential pulse voltammetry, and attempted electropolymerization reactions with acetonitrile solutions of the complexes, which were not successful. Each complex features a single iron(3+) reduction wave at approximately −0.7 V (versus ferrocene), and the oxidation of the 2,2′-bithienyl substituent occurs at +1.1 V. These materials represent a new structural paradigm for the study of rare bimetallic iron(3+) spin-crossover complexes