Exchange coupled clusters

Miinck E, Popescu CV. MoBbauer studies of exchange coupled cluster assemblies in biological systems. Hyperfine Interact. 2000 126(1 4) 59—67. 

Hence, the useful plots of x (usually calculated as MJH), xT and x T at fixed H, and M vs H at fixed (usually low) T, can be constructed. These data can provide a wealth of information on exchange coupled clusters. An increase in xT as T decreases is a signature of low lying states with big spin... 

The present book first recapitulates all the necessary mathematical background (Chapter 1). An overview of macroscopic magnetic properties is then presented (Chapter 2). Formulation of magnetic parameters and methods of their calculation are given in Chapters 3-6. A brief summary of magnetic behaviour is presented (Chapter 7). The core of the book deals with the temperature dependence of magnetic susceptibility for mononuclear complexes, dimers and exchange-coupled clusters (Chapters 8-11). 

The multiline form of the S2-state is the best characterized of the EPR signals arising from the The spectrum, shown in Figure 6, arises from a S= /2 spin state and is 1,900 G wide with 18-20 lines centered at g = 2. The spectrum is indicative of an exchange-coupled cluster of mixed-valent 42,44,45 observed for mixed-valent Mn model complexes... 

The molecular exchange-coupled clusters that show slow relaxation of the magnetization have since become known as single-molecule magnets (SMMs)... 

There have been a number of reviews of EPR studies of MNMs in the past 5 years [33-37] especially by Barra/Gatteschi and Mclnnes, and it is not the aim of the present chapter to repeat the content of those reviews in detail. From these reviews, it is clear that certain EPR studies of MNMs have become classics in their field and they are briefly outlined below. The reader is referred to the cited reviews and primary hterature for further detail. In addition, the quasi-biannual reports by CoUison and Mclimes provide useful comprehensive overviews of EPR studies on exchange coupled clusters, including biological systems, for the relevant years [38 1]. 

Desulforubidin was found in strains of the Desulfomicrobium genus and has been described as the sulfite reductase of this genus. The subunit composition and molecular mass are similar to what was observed for desulfoviridin. However, in desulforubidin all sirohydrochlorins are metalated as proved by Mossbauer spectroscopy (152). The as-isolated protein contains four [4Fe-4S] clusters two of them are exchange-coupled to two paramagnetic sirohemes. 

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