X-ray absorption Fe−K edge data on ferrous and ferric model complexes have been studied to establish a detailed understanding of the 1s → 3d pre-edge feature and its sensitivity to the electronic structure of the iron site. The energy position and splitting, and intensity distribution, of the pre-edge feature were found to vary systematically with spin state, oxidation state, geometry, and bridging ligation (for binuclear complexes). A methodology for interpreting the energy splitting and intensity distribution of the 1s → 3d pre-edge features was developed for high-spin ferrous and ferric complexes in octahedral, tetrahedral, and square pyramidal environments and low-spin ferrous and ferric complexes in octahedral environments. In each case, the allowable many-electron excited states were determined using ligand field theory. The energies of the excited states were calculated and compared to the energy splitting in the 1s → 3d pre-edge features. The relative intensities of electric quadrupole transitions...

A Multiplet Analysis of Fe K-Edge 1s → 3d Pre-Edge Features of Iron Complexes

The coordination chemistry of pyrazole-derived ligands

Spin-state transitions in metal complexes which are driven by a change of temperature T or pressure p are always associated with a considerable reorganization of molecular geometry. The change involves metal-ligand bond lengths R, bond angles, and a variation of ligand orientation. In particular, the elongation 4R by up to ∼ 10% occurring in the course of the LS → HS conversion produces an expansion of molecular volume ΔV ≌ 25 A3 per metal atom. The average crystal structure for given values of T and p is reproduced by the fractional occupancy of the individual structures of the high-spin (HS) and low-spin (LS) isomer. The transitions are reasonably well described by a number of theoretical models which are equivalent to the Bragg and Williams approximation of the Ising model. The dynamics of the spin-state transitions in solution, based on measurements by ultrasonic and photo-perturbation techniques, is in general rapid with rate constants between 4 × 105 and 3 × 108 s−1. Similar results are obtained for the spin conversion in solid complexes where the line shape analysis of Mossbauer spectra based on the theory of Blume and Tjon is applied. The dynamics may be rationalized employing one-dimensional cross sections through Gibbs free-energy surfaces G = G(R), an alternative being the comparison of the results with quantum-mechanical calculations for a radiationless non-adiabatic multiphonon process.

Nature and dynamics of the spin-state interconversion in metal complexes

Spin equilibria in iron(II) complexes

The spin-states and spin-transitions of mononuclear iron(II) complexes of nitrogen-donor ligands

Iron-nitrogen bond lengths in low-spin and high-spin iron(II) complexes with poly(pyrazolyl)borate ligands

Refined structure of CeKFe(CN)6·4H2O

Unit-cell constants for an isotypic series of hexagonal (P63/m) M(OH)3 where M = La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Y, Am and Cm are reported. Equations to determine the M–O distances were deduced. These calculated bond lengths are compared with experimental values. An independent set of ionic crystal radii for the metal ions was deduced and compared with reliable literature values.

Rare‐earth trihydroxide parameters

A structural refinement of ammonium hydrogen tartrate, C4H9NO6, has been completed from data obtained on an Enraf–Nonius CAD-4 X-ray diffractometer equipped with a Si(Li) solid-state detector. The refinement has given comparable results with those found in the literature. A comparative study of a select number of weak reflections obtained from this study and from the results of an analysis using a conventional scintillation system indicates that the peak-to-background ratio is better for intensity data collected on an X-ray diffractometer using a Si(Li) solid-state detector system. An important application of a Si(Li) energy-dispersive system is X-ray fluorescence analysis which can be performed on the same single-crystal employed in X-ray diffraction data collection. Qualitative determinations and quantiative data on relative percentages of metal constituents have been obtained from single crystals of Lu(OH)3 and Mn3[Co(CN)6]2.12H2O in less than two hours.

J. D. Oliver

Papers

Iron-nitrogen bond lengths in low-spin and high-spin iron(II) complexes with poly(pyrazolyl)borate ligands

Refined structure of CeKFe(CN)6·4H2O

Rare‐earth trihydroxide parameters

Applications of a solid-state detector on a modern single-crystal X-ray diffractometer

Metalation of a trialkylphosphine. Structure of bis(.mu.-chloro)bis[2-(di-tert-butylphosphino)-2-methylpropyl]dipalladium