Robbie G. McDonald

Notes. Electronic spectrum and metal–ligand bonding parameters of the V(H2O)63+ ion

The electronic spectrum of a crystal of NH4V(H2O)6(SO4)2·6H2O is reported and the transition energies interpreted in conjunction with previously reported magnetic susceptibility data using the angular overlap model. Satisfactory agreement with experiment can be obtained only if the π bonding in the plane of each water molecule is significantly weaker than that perpendicular to this plane.

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)

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 C1i, with unit-cell parameters a= 12.635(4), b= 11.513(3), c′= 8.094(3)A, 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)A, 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.

Normal coordinate analyses for the planar CuCl42− and CuCl2(H2O)2 complexes and their six coordinate analogues, the CuCl46− and CuCl4(H2O)22− anions

Abstract The vibrational data for the four coordinate trans square planar CuCl 2 (H 2 O) 2 complex are compared with those of the planar CuCl 4 2− anion. The results of normal coordinate calculations using a general valence force field approach are presented, and force constants obtained for CuCl 4 2− are used to define the force field of the CuCl 2 (H 2 O) 2 complex and to assign the (ClCuCl) out-of-plane bending mode of a u symmetry. The force constants calculated for the planar CuCl 4 2− and CuCl 2 (H 2 O) 2 complexes are also used to derive the force fields for their elongated six coordinate CuCl 6 4− and CuCl 4 (H 2 O) 2 2− relatives. Vibrational mean square amplitudes for all complexes are also reported and compared.

Unusual features in the polarised single crystal electronic spectrum of (NH4)2[V(H2O)6](SO4)2: Analysis of Fano antiresonance structure and bonding in the [V(H2O)6]2+ complex

Abstract A detailed analysis of the electronic spectrum of the V 2+ Tuttons salt (NH 4 ) 2 V(H 2 O) 6 (SO 4 ) 2 and its deuterate is presented. The spectra exhibit a number of unusual features including some not previously noted in earlier studies of this compound. In particular, there is structure superimposed on the 4 A 2g → 4 T 2g band envelope ascribed to Fano antiresonances, which is due to the interaction of the 2 E g and 2 T 1g spin forbidden states with the 4 T 2g state. The duplication of this structure in a much less intense band ∼ 3200 cm −1 to higher energy, suggests that the latter is induced by coupling of the 4 T 2g state to an OH stretching frequency, and this is confirmed by deuteration. A similar band coupled to the 4 T 1g (F) state is observed at ∼ 22000 cm −1 . From the spectral assignments, angular overlap model ligand field parameters are obtained and the bonding in the [V(H 2 O) 6 ] 2+ complex is discussed.

Crystal and molecular structure of chromium(II) sulphate pentahydrate and single-crystal electronic spectra and bonding of CrSO4·5H2O, CuSO4·5H2O, and CuSO4·5D2O

The crystal and molecular structure of CrSO4·5H2O is reported; this compound is isostructural with the analogous copper(II) salt. The two independent molecules in the unit cell have quite similar, tetragonally elongated ligand co-ordination geometries, the distortion from regular octahedral arrangements being marginally smaller than those in the copper(II) compound. The average Cr–O distance is ca. 0.07 A longer than the average Cu–O bond length, this difference being more marked for the in-plane than the axial bonds. The low-temperature single-crystal electronic spectrum of CrSO4·5H2O shows bands in the region 10 000–15 000 cm–1 assigned as d–d transitions coupled to metal–ligand vibrations and a weak peak at 18 450 cm–1 thought to be due to coupling with water O–H stretching vibrations. The spectrum of CuSO4·5H2O is also reported and is similar to that of the chromium(II) compound except that the bands are ca. 2 000 cm–1 lower in energy. For the copper(II) complex the assignment of the peak due to coupling with O–H stretches of the water molecules was confirmed by measuring the electronic spectrum of the corresponding deuteriated compound. An analysis of the transition energies using the angular overlap model suggests that the ligand interaction with the d orbitals is ca. 20% higher in the chromium(II) compound than in the copper(II) derivative. In both compounds the dz2 orbital is depressed in energy compared with the predictions of the simple bonding model, and better agreement with the observed transition energies is obtained if the π-bonding interaction involving the water molecules is approximately isotropic about the metal–ligand bond axes.