Oligonuclear systems

Once a description of the electronic structure has been obtained in these terms, it is possible to proceed with the evaluation of spectroscopic properties. Specifically, the hyperfine coupling constants for oligonuclear systems can be calculated through spin projection of site-specific expectation values. A full derivation of the method has been reported recently (105) and a general outline will only be presented here. For the calculation of the hyperfine coupling constants, the total system of IV transition metal centers is viewed as composed of IV subsystems, each of which is assumed to have definite properties. Here the isotropic hyperfine is considered, but similar considerations apply for the anisotropic hyperfine coupling constants. For the nucleus in subsystem A, it can be... 

Both types of additive names are exemplified below for oligonuclear systems. 

The isotropic exchange discussed so far represents only a portion of the total exchange interaction operating in binuclear and oligonuclear systems. 

It should be clear from the preceding examples that theoretical studies of this type serve not simply to validate computational predictions by detecting potential sources of error, but also to identify the origins of particular spectroscopic characteristics, establish trends, and uncover correlations between structural or electronic features and spectroscopic observables. It remains to be seen in future applications how far this approach can take us in establishing reliable connections between structural parameters and spectroscopic properties for larger and more complex oligonuclear transition metal systems. 

In this chapter we will present a series of polynuclear nickel(II) complexes, placing our attention mainly on those complexes for which the largest number of experimental observations are available. We will first review dimers and later oligonuclear complexes and extended systems in the order of increasing number of constituent metal ions. 

Structures which can be regarded as oligonuclear coordination entities may be named as such (Section IR-7.3) or may be named using the system for inorganic chains and rings (Section IR-7.4). 

As a radical, the 1,3-diborolyl ring system cannot exist independently but only in combination with one or two transition metal atoms. It can olfer three electrons to metal atoms by the C n-electrons, whereas the two B atoms act as acceptor centers towards the metals. In formulas (18)-(20) a mononuclear and several oligonuclear 1,3-diborolyl complexes are shown representatively. The ideal number of valence electrons (VE) in such a complex is 12n 6, where n is the number of stacks <88PAC1345>. 

The PND technique has now been widely applied to many dinuclear, oligonuclear, and onedimensional magnetic systems involving transition metal ions. 

Frosch, W. Back, S. del Rio, I. van Koten, G., and Lang, H. (1999). An Easy Entry to Novel Early-Late Oligonuclear Transition Metal Complexes Containing r-Conjugated Systems. Inorg. Chem. Commun., 2, 584-586. 

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