2. d d Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 2.1 Six-Coordinate Systems wi th Ground States o f Nondegenerate Octahectral Parentage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 2.1.1 Chromium(II I ) Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 2.1.2 Cohalt(III) Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 2.1.3 Nickel(II) Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 2.2 Six-Coordinate Iron(II) Sys tems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 2.3 Five-Coordinate Sys tems (other than d 9) . . . . . . . . . . . . . . . . . . . . . . . . . . 95 2.3.1 The Pentaeldorovanadate(IV) Ion . . . . . . . . . . . . . . . . . . . . . . . . . . 95 2.3.2 Cobalt(H) Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 2.3.3 Nickel(II) Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 2.4 Triatomic Dichlorides of the Transi t ion Metals . . . . . . . . . . . . . . . . . . . . . . 97 2.5 Copper(II) Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 2.5.1 CuN4X 2 Chromophores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 2.5.2 Copper(II) Halide Complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 2.5.3 Copper(II) Systems with Oxygen-donor Ligands . . . . . . . . . . . . . . . . . . 102 2.5.4 Five-Coordinate Copper(II) Sys tems . . . . . . . . . . . . . . . . . . . . . . . . . 104 2.5.5 Miscellaneous Copper(II) Systems . . . . . . . . . . . . . . . . . . . . . . . . . . 104 2.6 Other Aspects o f d d Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

Applications of the angular overlap model

ESR studies of alkylamine complexes of copper(II) imides: the CuN42− chromophore

The Interpretation of Ligand Field Parameters

Linear ligand fields influencing auger spectra of fluorides, copper(I) and silver(I)

Qualitative MO theory predicts degenerate dπ orbitals for planar coordination complexes with formally σ-only ligands and the splitting energy, ΔEπ = E(dxy) - E(dxz,dyz), should be zero. For π-donor ligands, ΔEπ should be positive (dxy > dxz,yz) while for π-acceptors, ΔEπ should be negative (dxy nEg > nB1g, n = 1 or 3, does not guarantee a d-orbital sequence of dxy < dxz,yz < dz2.

d-orbital energy levels in planar [MIIF4]2-, [MII(NH3)4]2+ and [MII(CN)4]2- complexes: the nature of M-L π bonding and the implications for ligand field theory.

The effects of symmetry-restricted covalence on the d–d spectra of tetra-amminecopper(II) compounds are discussed, with particular reference to the relative energies of the 2B2g and 2Eg states. The d–d transition energies are expressed as the sum of a change in one-electron energy and a change in two-electron energy. The latter terms are calculated in the INDO approximation; the necessary MO mixing coefficients are obtained by appeal to experimental data and a simple approximation based on perturbation theory. For square coplanar Cu(NH3)42+, it is shown that the 2B2g state should lie higher in energy than the 2Eg state if, as expected in a σ-bonded system, the b2g and eg orbitals are accidentally degenerate. This is contrary to the predictions of simple ligand field models. If axial ligands having π-donor orbitals are allowed to approach the metal, completing the usual tetragonal octahedral co-ordination geometry, the model predicts that, notwithstanding the destabilization of the eg orbitals as a consequence of axial π-interaction, the 2Eg state becomes higher in energy than the 2B2g state. These results are consistent with experimental data.

Symmetry-restricted covalence in ligand field theory. Part I. The relative energies of the 2B2g and 2Eg states in tetra-amminecopper(II) compounds

Rate coefficients of aquation at constant ionic strength in lithium perchlorate–perchloric acid media of a series of penta-ammine(carboxylato)cobalt(III) complexes [Co(NH3)5L]n+ have been calculated from u.v. absorbance measurements. With most of these, increases in the observed rate coefficients are not proportional to increases in the acid concentrations. The data have been used to calculate association constants of protonated forms of the complexes and the corresponding rate coefficients of aquation. The obtained association constants are 0.64 (L = acetate; I= 2.0, 40 °C), 0.1 (L =o-methoxybenzoate; I= 2.0, 40 °C), 116 (L = oxalate; first association constant, I= 0.5, 60 °C), 0.24 (L = malonate; second association constant, I= 2.0, 40 °C), 0.69 (L = succinate; second association constant, I= 2.0, 40 °C), 0.02 dm3 mol–1(L =o-phthalate; second association constant, I= 2.0 mol dm–3, 40 °C). With the tartrato-complex the observed rate coefficients increased linearly with increasing [HClO4] and this is also so with the oxalato-complex for I > 0.5 mol dm–3 but such increases are small when compared with those of the other d ica rboxylato-complexes of the present studies. U.v. spectral decreases at constant wavelength with increasing [HClO4] under virtually static conditions have also been used to estimate the association constants of the protonated complexes. The exceptions, since no spectral decreases were found, are the o-methoxybenzoato-complex, the oxalato-form at [HClO4] > 0.5 mol dm–3, and the doubly protonated tartrato-complex. The values obtained are 0.68 (L = acetate; I= 2.0, 30 °C), 125 (L = oxalate; first association constant, I= 0.5, 60 °C), 0.37 (L = malonate; second association constant, I= 2.0, 40 °C), 0.67 (L = succinate; second association constant, I= 2.0, 40 °C), 0.1 dm3 mol–1(L =o-phthalate; second association constant, I= 2.0 mol dm–3, 40 °C). These are in reasonable agreement with the above values derived from the kinetic data and from the latter the rate coefficients of aquation of the protonated species have been estimated. There appear to be broad relationships between the rate coefficients of the protonated forms and the association constants (comparing acetate with o-methoxybenzoate and succinate with malonate). This can perhaps account for the oxalate, tartrate, and o-phthalate complexes showing little evidence of double protonation. This feature is also discussed in terms of ligand chain lengths and it is also noted that in contrast to the first association constants of the protonated dicarboxylate complexes which are large but have relatively little catalytic effect, the second association constants are small but have strong influences upon the rates of aquation.

Influence of electrolytic dissociation upon rates of reactions. Part 10. Acid-catalysed aquations of some penta-ammine(carboxylato)cobalt(III) ions in aqueous solutions

Derek W. Smith

Papers

Symmetry-restricted covalence in ligand field theory. Part I. The relative energies of the 2B2g and 2Eg states in tetra-amminecopper(II) compounds

Influence of electrolytic dissociation upon rates of reactions. Part 10. Acid-catalysed aquations of some penta-ammine(carboxylato)cobalt(III) ions in aqueous solutions