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Self-assembled Transition Metal Coordination Frameworks of ...

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Chapter 4<br />

The solid state and some frozen DMF spectra recorded in a Varien E 112 EPR<br />

spectrometer in the X-band were very broad with no good hyperfine splittings. These<br />

kinds <strong>of</strong> spectra do not give much information but may be the presence <strong>of</strong><br />

antiferromagnetic interaction between copper(II) ions. Some <strong>of</strong> the room temperature<br />

powder spectra however exhibit some indications <strong>of</strong> weak triplet state lines at half<br />

fields <strong>of</strong> Cu(H)...Cu(H) interactions. So far, reports <strong>of</strong> EPR measurement <strong>of</strong> Cu(H)<br />

complexes <strong>of</strong> thiocarbohydrazone [12] and carbohydrazone [17] unfortunately do not<br />

give much information. The dimeric dicopper(H) compound <strong>of</strong> a similar<br />

thiocarbohydrazone [12] in H3PO4 frozen solution shows two monomeric axial Cu(H)<br />

species, one with a g" value <strong>of</strong> 2.33, somewhat similar behaviour <strong>of</strong> our study. The<br />

absence <strong>of</strong> any detailed EPR studies <strong>of</strong> similar multinuclear carbohydrazone or<br />

thiocarbohydrazone Cu(H) complexes with single crystal X-ray results for molecular<br />

structural corroborative studies still leaves the matter for further research. A detailed<br />

analysis <strong>of</strong> the EPR behavior by varying concentration in different solvents is found<br />

obligatory to get a clearer picture <strong>of</strong> labile multinuclear systems.<br />

4.3.5. Magnetochemistry<br />

For all the copper compounds the temperature dependence <strong>of</strong> molar magnetic<br />

susceptibility X,“ in the powder form is carried out in the temperature range 5-325 K.<br />

All compounds are found to show common features. The effective magnetic moments<br />

pm at room temperature <strong>of</strong> all dicopper(H) compounds are found to be low or near<br />

compared to that expected for two independent Cu(II) ions (2.45 pg) and also shows a<br />

regular decrease with decreasing temperature suggesting antiferromagnetic<br />

interactions between Cu(H) ions. The temperature dependence curves <strong>of</strong> 8, 9 and 13<br />

also show similar nature. These features indicate a dominant antiferromagnetic<br />

interaction in these compounds. Also it is found that Curie law is not obeyed by all<br />

systems, in agreement with the exchange coupling.<br />

170

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