Charge transfer salts of Tetracyanoquinodimethane (TCNQ) were
synthesised and their electrical and magnetic properties were
investigated. These salts show unusual electrical and magnetic
behaviour in contrast to conventional organic compounds. These
salts have crystal structures which in general consist of TCNQ
radical ions stacked in chains, isolated from each other by the
diamagnetic cations. They are thus regarded as "one-dimensional"
electrical and magnetic systems. The ESR spectra of these salts are
attributed to triplet excitons showing that the spin-spin and electronelectron
correlation effects are important. In the ESR spectra
(Chapter III) of some TCNQ salts dipolar splitting is observed
confirming the spin-spin interaction. These triplet excitons are
regarded as bound electron-hole pairs. The experimentally determined
dipolar splitting tensors are presented in Chapter III and the intensity
data in Chapter IV. A large number of fine structure lines are
observed in the ESR spectra of Pyridinium-TCNQ and 4-Aminopyridinium-TCNQ
apart from regular triplet exciton lines (Chapter III). These lines
are attributed to the trapping of excitons on an extended formula
finit (TCNQ2 )n. In Chapter IV the temperature dependent magnetic
susceptibilities are discussed in terms of Heisenberg antiferromagnetism
and Pauli paramagnetism. In Chapter V temperature
dependent behaviour of electrical conductivity is discussed in terms
of an exciton band model, the lattice structure of the salts and
one-dimensional lattice consisting of defects giving rise to high and
low conducting segments. Low temperature electrical and magnetic
phases are discussed (Chapters IV and VII) in terms of a band and
hopping mechanisms.In Chapter VI self consistent field calculations are made with
reference to the tight binding one electron band theory using
simplified Roothaan equations considering CNDO approximations.
Theoretical results are related to experimental band gaps, spinspin
interactions and charge alteration.
| Identifer | oai:union.ndltd.org:BRADFORD/oai:bradscholars.brad.ac.uk:10454/3512 |
| Date | January 1978 |
| Creators | Ahmad, Muhammad M. |
| Contributors | Shields, L. |
| Publisher | University of Bradford, Postgraduate School of Studies in Chemistry. |
| Source Sets | Bradford Scholars |
| Language | English |
| Detected Language | English |
| Type | Thesis, doctoral, PhD |
| Rights | <a rel="license" href="http://creativecommons.org/licenses/by-nc-nd/3.0/"><img alt="Creative Commons License" style="border-width:0" src="http://i.creativecommons.org/l/by-nc-nd/3.0/88x31.png" /></a><br />The University of Bradford theses are licenced under a <a rel="license" href="http://creativecommons.org/licenses/by-nc-nd/3.0/">Creative Commons Licence</a>. |
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