8.2.9 $^{133}$Cs(I) complex with 2,3-di-tert-butyl 1,3-diene anion radical [a030]

This ionic-pair formed by an anion radical associated with the cation $Cs^+$ presents 72 experimental lines (Fig. 36). The caesium with atomic mass number 133 has a natural abundance of the 100% and a value of I = 7/2; therefore, its coupling with the unpaired electron would give eight lines, octet $(2 \cdot 7/2 +1)$, of equal height (intensity). In the experimental spectrum the following points are observed:

a)

The lines 1-2-4 form a triplet with intensities 1:2:1.

b)

The lines 2-5-8 form another triplet, with intensity double of that of the previous one.

c)

Eight lines of equal height and constant separation, 5-14-23-32-41-50-59-68.

These experimental facts suggest that: 1) we have two splitting values very close that correspond to two groups with two hydrogen atoms, positions 1,4-exo and 1,4-endo of the butadieno, respectively; 2) the eight lines of the spectrum are due to the Cs, and this splitting is much higher than that of the triplets; 3) The hyperfine splitting owed to the 18 equivalent H of Terc-butyl is not detected.

[I] To measure the hyperfine splittings specially those of the triplets change the range of the experimental spectrum (from -10.20 to 0 mT). Compare the simulated with the experimental spectrum and refine the parameters until they overlap correctly.

Figure 36: EPR spectrum of the $^{133}$Cs(I) complex with 2,3-di-tert-butyl 1,3-diene anion radical.

Simulator