Spin-triplet ground state

A recent Mossbauer and magnetic susceptibility study on [Fe(phen)2ox] 5 H20 186) has identified this complex as a typical 5T2(0, ) 1Aj(Oh) spin crossover system rather than a complex with a spin triplet ground state. Moreover, it has been shown 186> that the magnetic properties are very susceptible to the amount of lattice water present Pumping off the lattice water gradually favours more and more the HS state the stable monohydrate, finally, turned out to be a paramagnet. 

Figure 12.17. 1.3-coupling in phenylene with spin-carrying substituent to yield a high-spin triplet ground state (adapted from reference [214]). 

Ligand field theory of spin triplet ground states in the d configuration of D4h and Djd symmetries. 

Gouy, Farad spin triplet ground state A2 suggested ... 

The classification into Kekule and non-Kekule diradicals is mainly based on the difference in their resonance structures. From the proceeding discussions, however, such a classification does not closely relate to the relative stabilities and spin preference of TT-conjugated diradicals. For example, some non-Kekule diradicals, such as 1 and 8, prefer a triplet ground state, but some others (like 7) have a singlet ground... 

Electron spin resonance (ESR) studies of the urazole-bridged 1,3 diradicals 64 derived from the azoalkanes 63 confirm a triplet ground state for these species. The nearly zero symmetry parameter, that is, Elhc= 0.0004 0.0001 cm-1, for the triplet diradical 64 of the diphenyl azoalkane 63 establishes a planar conformation <1995JOC308, 1997JA10673>. 

Since Fe(CO)4 has a triplet ground state its reaction with CO to form Fe(CO)5 should be spin forbidden [Eq. (9)]. 

Concerted fragmentation of the transition state in the peroxy radical recombination yields carbonyl compound molecules in the excited triplet state, alcohol in its singlet ground state, and oxygen in its triplet ground state, in fulfilment of the spin selection rules. 

Rather than focusing on the short-time photochemical reactivity, our interest in the spin-forbidden reactions of iron carbonyl fragments has been mainly in the longer-time thermal chemistry of the fragments produced. This is summarized in Scheme 3. As already stated, iron tricarbonyl and tetracarbonyl are known to have triplet ground states, and for many ligands, it is assumed that Fe(CO)3L would also have a triplet ground state. Hence many of the indicated processes are spin-forbidden. 

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