Ligand Field Theory & Spectra

Abstract

In any chemical environment – traditionally represented as a crystal field (CF), in which the donor atoms are represented by point charges – an n d subshell loses its fivefold degeneracy. The consequent splitting is described in detail for cubic (octahedral and tetrahedral) systems. The pure CF approach has serious shortcomings, but the effects of covalency can be accommodated without losing its simplicity altogether; this is often called ligand field theory (LFT). CF/LFT is important in the interpretation of the d–d spectra of complexes; the d–d states arising from cubic d n systems and their relative energies are analyzed, along with a discussion of the nephelauxetic effect. As examples of the analysis of d‐orbital splittings in noncubic complexes, chlorocuprates(II) and tetragonal tetraamminechromium(III) complexes are examined in detail, using the angular overlap and cellular ligand field models. Among applications of LFT, ligand field stabilization energy (LFSE) is useful in the rationalization of thermodynamic and kinetic observations. The Jahn–Teller effect is important in the structural chemistry of copper(II) especially.

Electronic Structure Evolution of SrCoOx during Electrochemically Driven Phase Transition Probed by in Situ X-ray Spectroscopy

“…Upon BM → P transition, T d crystal field transforms to O h coordination. The T d and O h crystal fields have different effects on the splitting the Co d orbitals, and the field strength for T d is much lower than O h . This difference between the T d and O h crystal fields is likely to alter the pDOS of Co at the top of VB, thus causing the evolution in RESPES observed as a function of applied bias.…”

“…The T d and O h crystal fields have different effects on the splitting the Co d orbitals, and the field strength for T d is much lower than O h . 30 This difference between the T d and O h crystal fields is likely to alter the pDOS of Co at the top of VB, thus causing the evolution in RESPES observed as a function of applied bias. Comparing our results with DFT calculations reported by Choi et al, 10 we can even tentatively link the intensity decrease at ∼2.6 eV to the diminished T drelated states and the intensity increase at ∼0.4 eV to the enhanced O h -related states, during the BM → P phase transition.…”

Crystallization via Oriented Attachment of Nanoclusters with Short-Range Order in Solution

“…UV−vis analysis of the reaction solutions (Figure S5a) indicated absorption bands at 375 and 525 nm, which are attributed to the d orbital splitting of Co due to the formation of Co(II)/NH 3 complex. 20 The intensities of two absorption peaks are proportional to the Co(II) concentration and, therefore, can be used to monitor the change of Co(II) concentration following a calibration curve (Figure S5b). 21 It can be seen that overall the cobalt(II) concentration decreased during the first 120 min with a small increase observed at 80 min (Figure S4).…”

“…The reaction solution was then heated at 90 °C for 24 h. The color and pH value of the solution were monitored during the reaction (Figure S4), which shows that the solution changed from brown (pH ∼9.8), to dark red (1 h, pH 8.5), to violet (2 h, pH 8.4), and eventually before became colorless (24 h, pH 7.8) with black precipitates formed at the bottom. UV–vis analysis of the reaction solutions (Figure S5a) indicated absorption bands at 375 and 525 nm, which are attributed to the d orbital splitting of Co due to the formation of Co­(II)/NH 3 complex . The intensities of two absorption peaks are proportional to the Co­(II) concentration and, therefore, can be used to monitor the change of Co­(II) concentration following a calibration curve (Figure S5b).…”

Transition Metal Ion Colors

“…All these colors arise from electronic transitions between the ionic ground state and energy levels lying between 1.77 and 3.10 eV above it, giving absorption maxima in the visible wavelength range (400-700 nm). These low-lying energy levels arise from interactions of the d orbitals on the cation with neighboring atoms in a material and are a function of the symmetry of the surroundings [1][2][3]. The energy levels that occur with the 4d and 5d transition metals are higher in energy than those of the 3d series and are of lesser importance in color terms.…”