Spin cluster

G. Cho, J.P. Yesinowski, H and F multiple quantum dynamics in Quasi-one-dimensional spin clusters in apatites, J. Phys. Chem. 100 (1996) 15716-15725. 

These values of the major Jy parameters are rather close to those obtained using the 2- and 4-spin clusters [4,5] and trend towards simultaneous decrease in each parameter on several percents with the increase in the cluster size so that the inequality Jn > l-/14 s J13 is satisfied in any case. 

The calculations were carried out by the pseudopotential method with SBK basis set (GAMESS codes [19,20]) see Refs. [4,5] for the details of calculations. aThe data for the 4-spin cluster [5] are shown for comparison. 

Jy obtained from 8-spin cluster (Table 1) and 12D (Table 2) are used. aAccording to Ref. [13]. 

Gatteschi, D. Pardi, L. Spin levels of high nuclearity spin clusters. In Research Frontiers in Magnetochemistry, O Connor, C. J. Ed. World Scientific Singapore, 1993. 

HAp is a good model compound for the study of DQ coherence excitation profile.85 The closest P-P distance in HAp is 4.143 A. The numerical simulations and the experimental data were shown in Figure 5. The maximum DQ coherence excitation efficiency decreases as the spin cluster size increases. The reason is simply due to the fact that all the spins in the cluster will contribute (different combinations of two spins) to the DQ coherence. The passive spins in close proximity would provide a strong dipolar dephasing of the excited DQ coherence. As expected, the simulation results converge towards the experimental data as the cluster size increases. 

The simulations correspond to different spin clusters containing 2-7 phosphorus spins. The geometrical parameters were taken from the X-ray structure of HAp. 

The [Mn9(/x-CN)3oMo6] core of the high-spin cluster. From J. Larionova, M. Gross, M. Pilkington, H. Andres, H. Stoeckli-Evans,... 

One of the key aspects of the design was to distribute weak fCUs in such way that a symmetrical spin cluster was obtained. Eigenvalues for Heisenberg Hamiltonian for such cluster could be readily solved, allowing for computation of both temperature and field dependence of magnetization for direct fitting of the experimental data.94,107 Therefore, additional structure-property correlation could be obtained. 

The practical implementation of organic spin clusters was through the synthesis of polyradicals, in which relatively weak and relatively strong fCUs were based upon 3,4 -biphenylene and 1,3-phenylene connectivities. Based upon the spin densities in conformationally unconstrained systems, factor of 6 was predicted for the relative strength of exchange coupling in 3,4 -biphenylene and 1,3-phenylene.3,107,108... 

Fig. 27 Design of high-spin organic spin cluster.

Macrocyclic-macrocyclic polyradicals consist of macrocyclic branches connected to macrocyclic cores via bis(3,4 -biphenylene)methyl linkers (Figs 32 and 33). The connection of calix[4]arene-based macrocycles via bis(3,4 -biphenylene)methyl linkers provided special type of organic spin clusters, in which large component spins of the macrocycles were exchange coupled via much smaller spins 1/2 of the linkers, as illustrated in Figs 32 and 33 for polyradicals 51-53.8 112... 

Fig. 32 Macrocyclic-macrocyclic organic spin clusters of unequal spins 51 and 52.112...

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