Transition metals spectra

The crystal-field interaction in lanthanide-ion spectra in solids is weak in the sense that perturbations that shift the positions of the free-ion levels are small (compared to corresponding shifts in transition-metal spectra) and the effects of coupling different free-ion levels by the crystal field are small. The weakness of the lanthanide crystal-field interaction is a consequence of the shielding of the 4r configuration by the outer 5s and 5p atomic shells and is reflected in the historical sequence of theoretical advances in lanthanide crystal-field theory. 

The extended fine structures are well observed in 3d- and 4d-transition metal spectra. MW SEFS spectra from Cr to Cu and Ag NW SEFS spectra, as well as Fe and Ni LW SEFS spectra and Ag MW SEFS spectra, have been obtained. 

We will discuss applications of the APS technique to simple as well as multicomponent systems. The results of the applications cited are compared with those from other techniques wherever available. The derivation of the DOS directly from the APS spectrum of 3d transition metals has been dealt with by various authors (Dose et al. 1981). The one-electron theory explains satisfactorily the 3d transition metal spectra, but fails when applied to the lanthanide metals. The electronic structures of the lanthanide metals and their intermetallics as obtained from APS spectra are also discussed. 

In the following sections examples of pressure effects are discussed under four headings rare earth spectra, transition metal spectra, heavy metal ions in the alkali halides, and color centers in the alkali halides. In addition to discussing the results of current experiments, we point out those areas where further efforts should be most fruitful. 

Applying this model, the 4f doublet of Th metal would appear to be a typical 5f-transition metal spectrum (i.e., with a split doublet where the 5 fs play the screening role of the d electrons in a d-transition metal). This is consistent with strong hybridization of 5f and (d, s) states as predicted by theory ... 

The aromatic shifts that are induced by 5.1c, 5.If and S.lg on the H-NMR spectrum of SDS, CTAB and Zn(DS)2 have been determined. Zn(DS)2 is used as a model system for Cu(DS)2, which is paramagnetic. The cjkcs and counterion binding for Cu(DS)2 and Zn(DS)2 are similar and it has been demonstrated in Chapter 2 that Zn(II) ions are also capable of coordinating to 5.1, albeit somewhat less efficiently than copper ions. Figure 5.7 shows the results of the shift measurements. For comparison purposes also the data for chalcone (5.4) have been added. This compound has almost no tendency to coordinate to transition-metal ions in aqueous solutions. From Figure 5.7 a number of conclusions can be drawn. (1) The shifts induced by 5.1c on the NMR signals of SDS and CTAB... 

An important property of the surface behaviour of oxides which contain transition metal ions having a number of possible valencies can be revealed by X-ray induced photoelectron spectroscopy. The energy spectrum of tlrese electrons give a direct measure of the binding energies of the valence electrons on the metal ions, from which the charge state can be deduced (Gunarsekaran et al., 1994). 

At the other end of the conduction spectrum, many oxides have conductivities dominated by electron and positive hole contributions to the extent that some, such as Re03, SnOa and tire perovskite LaCrOs have conductivities at the level of metallic conduction. High levels of p-type semiconduction are found in some transition metal perovskites especially those containing alio-valent ions. Thus the lanthairum-based perovskites containing transition metal ions, e.g. LaMOs (M-Cr, Mn, Fe, Co, Ni) have eirlranced p-type semiconduction due to the dependence of the transition metal ion valencies on the ambient... 

Figure 2.86 The 1H NMR spectrum in the hydride region of the isomers of [IrH3(PEt2Ph)j] top, /ac-isomer bottom, mer-isomer. (Reproduced with permission from E.L. Muetterties (ed.), Transition Metal Hydrides, published by Marcel Dekker, 1971, p. 80.)...

In an earlier work, we have proposed a theoretical procedure for the spectroscopy of antiferromagnetically (AF) coupled transition-metal dimers and have successfully applied this approach to the electronic absorption spectrum of model 2-Fe ferredoxin. In this work we apply this same procedure to the [Fe2in - 82) P o - CeH48)2)2 complex in order to better understand the electronic structure of this compound. As in our previous work" we base our analysis on the Intermediate Neglect of the Differential Overlap model parameterized for spectroscopy (INDO/S), utilizing a procedure outlined in detail in Reference 4. 

A supramolecular assembly of macromolecules bearing antenna dendron has been reported. Pyrazole-anchored PBE dendrons were synthesized to examine the coordination behavior to transition-metal cations (Cu, Au, Ag) [31]. Self-assembled metallacycles were found. The Cu-metallacycle further formed luminescent fibers about 1 pm in diameter. The luminescence (605 nm) occurred by the excitation of the dendron (280 nm) and the excitation spectrum was coincident with the absorption spectrum of the dendron, suggesting the antenna effect. Interestingly, the luminescence of the Cu-metallacycle fiber disappeared when the fiber was dissociated into the individual metallacycles in C2H2. 

As a contradistinction to the relatively simple case of AI2O3 Cr(III) where the color is due to a metal-centred electronic transition, we mention now on one hand the fact that the Cr(III) ion colors many transition-metal oxides brown (e.g. rutile Ti02 or the perovskite SrTi03 [15]), and on the other hand the fact that the color of blue sapphire (AI2O3 Fe, Ti [16]) is not simply due to a metal-centred transition. By way of illustration Fig. 1 shows the diffuse reflection spectrum of SrTiOj and SrTi03 Cr(III) [17], and Fig. 2 the absorption spectrum of Al203 Ti(III) and Al203 Ti(III), Fe(III) [18]. It has been shown that these colors are due to MMCT transitions and cannot simply be described by metal-centred transitions [19],... 

Stable Mn(HI) compounds, Mn(R2r fc)3, have been known for a long time (42, 46). The structure of Mn(Et2C tc)3 is elucidated (47). The inner geometry of the Mn(CS2)3 core does not conform to the usual D3 point symmetry of transition metal complexes of this type, but shows a strong distortion attributed to the Jahn-Teller effect. The electronic spectrum (48, 49) and the magnetic properties of this type of complexes are well studied (50). 

The only doubly bonded tin compound for which the IR spectrum has been reported is the stannaketenimine [2,4,6-(CF3)3C6H2]2Sn= C=N[2,4,6-(CH3)3C6H2)]. The C—N stretching vibration (2166 cm-1) is shifted relative to that of mesityl isocyanide (2118 cm-1) this phenomenon is also observed for isocyanide-transition-metal complexes.87... 

This is a simplified Hamiltonian that ignores the direct interaction of any nuclear spins with the applied field, B. Because of the larger coupling, Ah to most transition metal nuclei, however, it is often necessary to use second-order perturbation theory to accurately determine the isotropic parameters g and A. Consider, for example, the ESR spectrum of vanadium(iv) in acidic aqueous solution (Figure 3.1), where the species is [V0(H20)5]2+. 

In addition to the simple chemical methods for following these processes, infrared spectroscopy may also be used. In Fig. 9 is shown the spectrum of silica dried at 200°C before and after reaction with Zr(allyl)4- The characteristic absorption bands of the transition metal-allyl group are clearly displayed, also a significant reduction in the number of hydroxyl groups (3740 cm-1) is also clearly evident. 

The value of -NMR and 13C-NMR spectroscopy in characterizing transition metal carbene complexes was noted in Section III,B,2. The carbene carbon resonance is invariably found at low field (200-400 ppm) in the 13C-NMR spectrum, while protons attached to Ca in 18-electron primary and secondary carbene complexes also resonate at low fields. NMR data for some Ru, Os, and Ir alkylidene complexes and related compounds are given in Table V. 

---