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Self-assembled Transition Metal Coordination Frameworks of ...

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Chapter 3<br />

charge transfer bands. For compound 6 also the S—>Ni charge transfer band at 22470<br />

cm" masks the possible d -d bands in that region. For compound 7 the CT band is<br />

obtained at 24150 cm", assigned S—>Ni LMCT. Another absorption obtained at 31250<br />

cm" is assigned as n —> 71' * transition. For a diamagnetic Ni(II) complex, as a<br />

consequence <strong>of</strong> eight electrons being paired in the four low-lying d orbitals with the<br />

upper orbital being d ‘Z , _ the four lower orbitals are <strong>of</strong>ten so close in energy that<br />

- -y<br />

individual transitions from them to the upper d level cannot be distinguished<br />

resulting in a single absorption band. The shoulder band obtained at 193 80 cm" for 7<br />

is attributed to the d -d band <strong>of</strong> this type. The d —d bands appearing as weak<br />

shoulders centered around the 20,000 cm" region are typical <strong>of</strong> square planar<br />

monoligated Ni(H) complexes [38].<br />

Table 3.4. Electronic spectral features <strong>of</strong> the Ni(H) thiosemicarbazone complexes<br />

and their free ligands.<br />

96<br />

Con7}_pounds Absorbance features km“ cm" (8 M"cm")<br />

HL 34480 (139900), 31850 (150500), 30860 (155100),<br />

29410 (165800), 28250 (161200)<br />

[Ni(HL7);]Cl; (5) 31250 (23640), 24510 (23230), 20750 (25280)<br />

HL8 36230 (8300), 29590 (9800), 23580 (2270)<br />

[Ni(HL8)L8]ClO4- 7H;O (6) 30030 (16550), 26530 (18080), 22470 (21200)<br />

[NiL3Cl]- '/2H3O (7). 31250 (7770), 24150 (12960), 19380 (1870)<br />

25*29 20* 25­<br />

. Q5­W<br />

+<br />

Q0­<br />

1 1 1 - 1 - 1 1 1 1 1 1 1 Q0 &<br />

=°°‘°°*°"°°°’°°'°°°°° ‘..;.,*..t;.,*.:,@‘.1.,"1a.,‘.1.*.e,.<br />

wav°'°"9th (nm) Wavelength (nm)<br />

Sin 10"‘M DMF 6in10‘4MDMF<br />

Fig. 3.18. Electronic spectra <strong>of</strong> Ni(I1) thiosemicarbazone complexes.

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