Magnetically-induced quadrupole splittings

Further experimental examples of temperature-dependent and magnetically-induced quadrupole splittings are provided in the first volume of this book (Chap. 6, see CD-ROM, Part VI) and also in Sect. 9.4 in Chap. 9 of the present volume. 

Quadrupole splitting (A q) correlates to electric field gradient and, based on model compounds, can identify some ligand types Can observe changes in ligand field induced by sample perturbation Can only detect iron sites Magnetic circular dichroism (MCD) spectra Require low temperature to observe (—2-70 K)... 

The use of external magnetic field makes it possible to determine the sign of the quadrupole splitting from the induced magnetic pattern (Giitlich et al. 1978) in the case of Fe and " Sn spectroscopy of nonmagnetic materials. 

Figure 9.12 shows the crystal structure of [Fe(pyrazine) Pt(CN)4 ] [13]. This complex shows a thermally induced spin-crossover transition (Tct = 284 K, T l = 308 K) with a thermal hysteresis of 24 K, which was observed by means of magnetic susceptibility measurement and Raman spectroscopy. The spin-crossover transition has been confirmed by Fe Mossbauer spectroscopy [13]. The Mossbauer spectrum at 300 K in the cooling mode consists of a single doublet with quadrupole splitting (QS) of 1. 159(5) mm s and isomer shift (IS) of 1.047(3) mm s whose values are typical of the HS state ( T2g, S = 2) of Fe(ll). At 80 K, a new doublet with quadrupole splitting of 0.306(4) mm s and isomer shift of 0.439(2) mm s whose values are typical of the LS state ( A g, 5 = 0) of Fe(ll). The photoinduced spin conversion between the LS and HS states around room temperature has been confirmed by means of Raman spectroscopy within the thermal hysteresis loop of spin-crossover transition, which is shown in Fig. 9.13 [13]. In this complex, the frequency of...

S04 ions were compared with the results of quantum-chemical calculations. Manninen et al. presented an analytic response theory formulation for the leading-order magnetic field-induced and field-dependent quadrupole splitting in nuclear magnetic resonance spectra by first-principles calculations for Ne, Ar, and Kr in noble gas atoms. The case of molecules was studied for in the sulphur hexafluoride molecule. 

The perturbation of the four substates of the excited 7 = 3/2 manifold by induces a typical asymmetry of the resulting magnetically split Mossbauer spectrum as pictured at the bottom of Fig. 4.10 for positive the inner four lines, 2-5, are shifted to lower velocities, whereas the outer two lines, 1 and 6, are shifted to higher velocities by equal amounts. In first order, the line intensities are not affected. For negative the line asymmetry is just inverted, as the quadmpole shift of the nuclear 1/2 and 3/2 states is opposite. Thus, the sign and the size of the EFG component along the field can be easily derived from a magnetic Mossbauer spectrum with first-order quadrupole perturbation. 

---