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Synthesis, structure and properties of some transition metal hexafluorophosphate and hexafluoroarsenate complexes Morrison, Raymond Maxwell


A number of pyridine, 3-methylpyridine, and 4-methyl-pyridine complexes of cobalt(II), nickel(II), and copper(II) hexafluorophosphate and hexafluoroarsenate have been synthesized and characterized. The physical methods of investigation which were used include vibrational spectroscopy, electronic spectroscopy, elemental analysis, and magnetic susceptibility measurements. In addition characterization of some complexes included single crystal and powder X-ray diffraction studies, electron spin resonance spectroscopy, mass spectrometry, and differential thermal analysis. The compounds studied were of two types, those containing non-coordinated hexafluorometallate anions and those with coordinated anions. The compounds in the former class have the composition M(py)₆(EFg)₂, M(4mepy)₈(H₂O)₂ (EF₆)₂, M'(3mepy)₆(H₂O)₂(EF₆)₂, and M"L₄(EF₆)₂ ( where M is Co and Ni, M' is Co, Ni, and Cu, M" is Co, and L is pyridine, 3-methylpyridine, and 4-methylpyrid;ine, and E is P and As) The compounds in the latter class are NiL^(EF₆)₂ and CuL4(EF₆)₂. Spectral and magnetic studies on the M(py)₆(EF₆)₂ compounds show them to contain the cationic species M(py)₆²⁺, where six pyridine ligands are octahedrally coordinated to the metal ion. Single crystal X-ray diffraction studies on Co(4mepy)₈(H₂O)₂(PF₆)₂, Ni(4mepy)₈(H₂O)₂(PF₆)₂, and Ni(3mepy)₆₋ (H₂O)₂(PF₆)₂ show the metal ion to be coordinated by four nitrogen donors and two oxygen (H₂O) donors in these complexes. Based on comparisons of electronic spectra and magnetic properties, the structures of all M(4mepy)₈(H₂O)₂(EF₆)₂ and M'(3mepy) ₆ (H₂O)₂(EF₆)₂ compound are considered to be similar. Spectral and magnetic studies on the CoL₄(EF₆)₂ complexes indicate they contain the cationic species, CoL₄²⁺where four nitrogen ligands are tetrahedrally coordinated around the cobalt(II) ion. This structure has been confirmed by a single crystal X-ray diffraction study on Co(4mepy)^(PF₆)₂. The anion bands in the infrared spectra of this class of compounds indicate that the EF₆⁻ ions have octahedral (O[sub h]) symmetry, although low site symmetry effects are evident. Studies on the compounds containing coordinated anions, included a consideration of criteria for anionic coordination based on the electronic properties of the metal ion, molecular structure of the complex and vibrational spectra of the anions. The electronic properties of the metal ion in the NiL₄(EF₆)₂ complexes indicate that the four nitrogen donors are strongly bound with square planar stereochemistry about nickel. The infrared spectra of the anions and the results of a single crystal X-ray diffraction study on Ni(4mepy)₄₋ (PF₆)₂ indicate that the EF₆⁻anions are very weakly coordinated in axial positions. The complex, Ni(py)₄(AsF₆)₂, is unique in that, while its structure is like that of other NiL₄(EF₆)₂ complexes at room temperature, it undergoes an isomerization from 220 to 160 K to a different low temperature isomer. The electronic properties of the nickel(II) ion and the vibrational spectra indicate that the anions are more strongly coordinated in the low temperature isomer. The electronic properties and vibrational spectra of the CuL₄(EF₆)₂ complexes indicate that both the nitrogen ligands and the anions are coordinated to the copper, with tetragonally distorted octahedral stereochemistry around copper(II). The strength of anion coordination in these copper complexes is considered to be comparable to that present in the low temperature isomer of Ni(py)₄(AsF₆)₂ and to be significantly greater than that present in all other nickel complexes studied.

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