Brandon Djukic

Preparation and Magnetic Properties of Iron(3+) Spin-Crossover Complexes Bearing a Thiophene Substituent: Toward Multifunctional Metallopolymers

The synthesis of a new 3-ethynylthienyl-substituted QsalH ligand (QsalH is the short form for N-(8-quinolyl)salicylaldimine) (ThEQsalH 3), and the preparation, electronic, and magnetic properties of three homoleptic and cationic iron(3+) complexes containing this ligand with PF(6)(-) 4, SCN(-) 5, and ClO(4)(-) 6 counteranions are reported. In all three complexes a spin-crossover is observed in the solid state by variable temperature magnetic susceptibility measurements and Mossbauer spectroscopy, indicating that the synthetic modification of the QsalH ligand has not significantly altered the electronics at the metal center. This includes the observation of a very rare S = 5/2 to 3/2 spin-crossover in a non-porphyrin iron(3+) complex 5. The molecular structure and magnetic properties of an unusual iron(2+) complex 7 generated by reduction of complex 6 serendipitously during a recrystallization attempt in aerobic acetone solution is also reported. Complexes 4-6 feature iron(3+) reduction and oxidation of the thiophene ring at potentials of approximately -0.7 and +1.2 V (vs Fc), respectively.

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.

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).

Synthesis of bromine- or aryl-substituted ditopic Schiff base ligands and their bimetallic iron(II) complexes: electronic and magnetic properties

Syntheses of three new ditopic Schiff base ligands bearing bromine, phenyl or 2-thienyl substituents are described. Bimetallic iron(II) complexes were prepared from these ligands and were characterized. Electrochemical measurements suggest no measurable electronic coupling between the metal ions in each complex. Variable temperature magnetic susceptibility measurements indicate gradual spin-crossover is operative in the complexes studied, with the low-spin state as the ground state in all cases. Density functional theory calculations corroborate these experimental observations. Attempts to electropolymerize the 2-thienyl-substituted complexes were not successful.

5,7-Di-2-pyridyl-2,3-dihydro­thieno[3,4-b][1,4]dioxine

The title compound, C16H12N2O2S, was prepared by a Neigishi cross-coupling reaction to investigate the coordination chemistry of thiophene-containing ligands. In the molecule, the pyridine rings are twisted from the thiophene ring by 20.6 (1) and 4.1 (2)°. The six-membered dihydrodioxine ring is in a half-chair conformation.

N′-(3-Thienylmethyl­ene)pyridine-2-carbohydrazide

The title compound, C11H9N3OS, was prepared to investigate the coordination chemistry of thiophene-containing ligands as precursors to interesting metallopolymers. The molecule is nearly planar. The angle between the thiophene and pyridine rings is 8.63 (4)° and features the expected trans configuration about the imine bond. The structure is stabilized by a weak intermolecular N—H⋯O hydrogen bond. The distance between centroids of adjacent thiophene rings [3.67 (8) Å] suggests the presence of π–π interactions.