Paramagnetic clusters

Reaction of thiophenol with Mo2Co2(/43-S)4(CO)2(t -CsH4Et)2 formed the electron-deheient, paramagnetic cluster [Mo2Co2(/f3-S)4(SPh)2(( -C3H4Et)2]. which, in the presence of CO, regenerated the original carbonyl cluster and afforded PhSSPh. The combination of these two reactions constitutes the basis of a catalytic cycle (Fig. 67). 

In an effort to make the distannyne, Ar Sn=SnAr (Ar = 2,6-(2,4,6-Pr 3C6H2)2C6H3), Ar SnH was heated in toluene hydrogen was eliminated but SnC bonds also were cleaved, and gave the paramagnetic cluster Ar 3Sn9 59 (g= ca. 2.031), with a structure that is based on the 21-electron [Sng]3- cage that is known as a Zintl ion.478... 

The dynamic properties of paramagnetic clusters are difficult to assess experimentally. The EPR spectra of the paramagetic ions are not particularly informative... 

The oxidized state [4Fe-4S]2+ is diamagnetic in its ground state, due to antiferromagnetic coupling of the two ferric and the two ferrous ions. However, at room temperature excited paramagnetic states of the cluster can be populated. Due to effective relaxation EPR signals of these paramagnetic clusters are usually only detectable at T < 35 K. In the reduced state the [4Fe-4S]l+ cluster... 

The strong tendency for cobalt to form paramagnetic clusters has been related to the accommodation of the unpaired electron in a low-lying cluster anti-bonding orbital derived mainly from the Co dz2 orbitals, thereby enlarging the cluster to dimensions suitable for incorporation of the carbon... 

Martin, R. L., Metal-metal interaction in paramagnetic clusters, in New Pathways in Inorganic Chemistry (E. A. Ebsworth, A. G. Maddock, and A. G. Sharpe, eds.) pp. 175-231. University Printing House, Cambridge, England, 1968. 

EPR measurements show the existence of paramagnetic clusters, magnetic susceptibility data reveal magnetic moments indicative of fewer than one unpaired electron per cluster. Nine-atom 9" clusters also occur in binary phases, but tetrahedral four-atom 4 clusters are predominant beside the arachno-typs 5 clusters. 

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