a Study of the Structural, Magnetic, Optical, and Electronic Properties of Several New Copper(ii) Halide and Copper(ii, i) Halide Compounds in the Solid State.
Abstract
The synthesis, x-ray crystal structures, magnetic susceptibilities, and ligand field transition energies are reported for several A_2Cu _2X_6 (A = organic cation; X = Cl, Br) compounds. The structure of the Cu _2Br_6^{2 -} dimer within these solids is correlated to their magnetic exchange and ligand field spectral results; the critical structural parameters tied to these properties are the geometry of the X-Cu-X bridge, and the coordination geometry about the metal centers. Spectral assignments are made in light of EHMO calculations. The synthesis, x-ray structures, and the polarized ligand field and charge transfer absorption results on the two room temperature phases of ((C_3 H_7)_4N) _2Cu_2Br _6 are presented. Striking piezochromic and thermochromic phase transitions are observed between these two phases. The optical properties associated with these phase transitions are explained in terms of a difference in orientation of the Cu_2Br _6^{2-} chromophore within each of the two phases. An absorption band unique to the dimer (not observed in the CuBr_4^ {2-} monomer) is assigned to a ligand to metal charge transfer transition, and not to a simultaneous ligand field transition occurring on each metal center. The synthesis, x-ray structure, absorption spectroscopy, magnetic susceptibility, and electronic conductivity results for a series of mixed-valence Cu(II,I) halide compounds are reported. These compounds fall into the following two categories: a family of pseudo 1-D compounds with the stoichiometry ACu_2X_4 (A = tetraalkylammonium cation, X = Cl, Br), and the compound (hydrazinium)_2Cu _3Cl_6. All of the compounds contain bridges of the type Cu(I)-X-Cu(II). It is shown via absorption spectroscopy and EHMO results that all of these compounds contain intervalence charge transfer bands. The 1-D salts show semiconductive behavior. The physical properties of the 1-D salts are rationalized in terms of band calculations. All compounds are assigned to Class II in the Robin and Day classification scheme. A series of compounds of the stoichiometry (paraquat)Cu _2X_4 (X = Cl, Br, I) are investigated using x-ray crystallographic, EPR, magnetic susceptibility, differential scanning calorimetry, and electrical conductivity techniques. X-ray results show all three compounds to be pure copper(I) in character. Magnetic susceptibility results show small copper(II) contributions in the chloride and bromide analogs. In the chloride salt the copper(II) ions appear to be incorporated into the (Cu_2Cl_4) _infty chain, with accompanying vacancies to provide for charge balance. In the bromide salt a Cu_2Br_6^ {2-} dimer appears to be incorporated into the chain structure. The chloride and iodide salts show insulating behavior, but the bromide salt shows enhanced conductivity.
- Publication:
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Ph.D. Thesis
- Pub Date:
- 1990
- Bibcode:
- 1990PhDT.......323S
- Keywords:
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- Chemistry: Physical; Chemistry: Inorganic; Physics: Condensed Matter