Spin-containing molecules

Methane-to-methanol conversion by gas-phase transition metal oxide cations has been extensively studied by experiment and theory see reviews by Schroder, Schwarz, and co-workers [18, 23, 134, 135] and by Metz [25, 136]. We have used photofragment spectroscopy to study the electronic spectroscopy of FeO" " [47, 137], NiO [25], and PtO [68], as well as the electronic and vibrational spectroscopy of intermediates of the FeO - - CH4 reaction. [45, 136] We have also used photoionization of FeO to characterize low lying, low spin electronic states of FeO [39]. Our results on the iron-containing molecules are presented in this section. 

All the results are summarized in Fig. 23 and serve as the first positive operational test for the McConnell theory. It is also noted that the orientational mode of stacking of spin-containing benzene rings can be useful in aligning spins parallel or antiparallel between high-spin aromatic molecules. 

In comparison with hydrocarbons, aromatic amines easily transform into cation radicals. Structures of these cation radicals are well documented on the basis of their ESR spectra and MO calculations (see, e.g., Grampp et al. 2005). The stable cation radical of A/,A,A, A -tetramethyl-p-phenylenediamine (the so-called Wuerster s blue) was one of the first ion radicals that was studied by ESR spectroscopy (Weissmann et al. 1953). The use of this cation radical as a spin-containing unit for high-spin molecules has been reported (Ito et al. 1999). Chemical oxidation of N,N -bis [4-(dimethylamino)-phenyl-A/,A -dimethyl-l,3-phenylenediamine with thianthrenium perchlorate in -butyronitrile in the presence of trifluoroacetic acid at 78°C led to the formation of the dication diradical depicted in Scheme 3.58. 

The problem of the ferromagnetism of a solid ion-radical salt has two important points. One is ferromagnetism at the level of a salt as the molecule, which consists of two paramagnetic species. Another is ferromagnetism at the level of a solid sample formed from assemblies of the spin-bearing molecules. These molecules may contain one or more magnetic centers. 

Problem 13.15 Although all elections spin, only molecules containing unpaired electrons—only free radicals—give esr spectra. Why is this (f/// . Consider the possibility (a) that one electron of a pair has its spin reversed, or (b) that both electrons of a pair have their spins reversed.)... 

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