Electron spin resonance spectra and crystal and molecular structures of magnetic-dipole coupled bis(1,4-dioxane-O)bis[(p-methoxybenzoyl)-trifluoroacetonato-O,O′]copper(II) bis(1,4-dioxane) solvate and catena-µ-(1,4-dioxane-O,O′)-bis[(p-nitrobenzoyl)trifluoroacetonato-O,O′]-copper(II)

Abstract

The crystal and molecular structures of the title compounds, [Cu(mbtfac)2(diox)₂]·₂diox [mbtfac =(p-methoxybenzoyl)trifluoroacetonate, diox = 1,4-dioxane] and [{Cu(nbtfac)₂(diox)}_n][nbtfac =(p-nitrobenzoyl)trifluoroacetonate] are reported. The former compound belongs to the triclinic space group C¹_i, with unit-cell parameters a= 12.635(4), b= 11.513(3), c′= 8.094(3)Å, α= 70.57(2), β= 81.07(3), γ= 70.47(2)°, and Z= 1 and consists of isolated, tetragonally distorted, octahedral molecular units with a pair of trans monodentate dioxane ligands and two lattice molecules of dioxane per copper. The latter is monoclinic with unit-cell parameters a= 15.753(4), b= 11.262(3), c= 7.587(2)Å, β= 91.72(2)°, and Z= 2 and involves a similar copper co-ordination geometry, but with the axial bonds being in this case to bridging dioxane ligands which link the metal ions to form an infinite, one-dimensional polymer. Both compounds show unusual, nine-line e.s.r. spectra when the magnetic field lies parallel or close to the shortest crystal axis. This is interpreted as being caused by a combination of magnetic-dipole coupling with the unpaired electron spins of the copper ions located at ± one unit along this axis, and the copper hyperfine interaction, the electron–electron dipolar splitting approximately equalling one-half the hyperfine interaction. In both complexes the electron exchange between the copper ions is slower than the e.s.r. time-scale. The lineshapes and anisotropy of the single-crystal e.s.r. spectra can be satisfactorily simulated using a simple point-dipole model which involves an inter-dipole separation and orientations of the molecular units which are in satisfactory agreement with those suggested by the X-ray structure determinations.