A series of palladium and platinum complexes of verdazyl radicals were prepared
to study the intermolecular magnetic exchange coupling. Reaction of bidentate verdazyl
radicals with (RCN)2MCl2 (R = Me or Ph; M = Pd or Pt) yielded square planar
(verdazyl)MCl2 complexes. The isolated complexes crystallized in either an infinite 1D
array or as loosely associated p-stacked dimer pairs. Molecules stacked with either M–M
or M–N(verdazyl) close contacts. Molecules that stacked with a M-M close contact
exhibited weak antiferromagnetic coupling. Molecules that stacked with a M–
N(verdazyl) close contact had coupling that was an order-of-magnitude weaker, but the
type of exchange was also metal dependent. While the palladium complex exhibited
weak antiferromagnetic coupling, the exchange in the analogous platinum complex was
ferromagnetic. The difference between the two was attributed to increased spin leakage
onto the platinum centre relative to palladium. The differing electronic behaviour of the
two metals was evident in the data from EPR and UV/vis spectroscopies.
Ruthenium complexes of a verdazyl radical were prepared by the reaction of a
bidentate verdazyl with Ru(L)2(MeCN)2 (L = acac or hfac). The complexes were isolated
in two or more oxidation states and all characterized by FT-IR, UV/vis/NIR, and EPR
spectroscopies, and their structures determined by X-ray crystallography. Experimental
data was further explained and supported with time-dependant DFT calculations which
were performed by Dr. A. B. P. Lever at York University, Toronto, Ontario. When the
complex contained an electron-rich metal fragment, Ru(acac)2, noninnocent behaviour
was observed. There was a large degree of orbital mixing, so that the spin distribution
was approximately 39% metal and 56% ligand. The contrasting complex with the
electron-poor fragment, Ru(hfac)2, behaved more innocently, the majority of charge was
localized and the spin was ligand-based.
Verdazyl-bridged diruthenium complexes were prepared from a bisbidentate
verdazyl and Ru(L)2(MeCN)2 (L = acac or hfac) to study the effect of a neutral radical
bridge on mixed-valence properties. Structural data from X-ray crystallography,
spectroscopic data from EPR, FT-IR, and UV/vis/NIR spectroscopies, and comparison to
the mononuclear ruthenium-verdazyl complexes were used to assess the charge
distribution in these complexes. The complex in which the verdazyl ligand bridged two
electron-rich metal centres exhibited a NIR absorption at approximately 1716 nm.
Together, this long wavelength transition and the structural data indicate a delocalized
electronic structure, [RuIII−vd–−RuII « RuII−vd•−RuII « RuII−vd–−RuIII]. The EPR
spectrum was also consistent with the delocalization of ligand spin onto the ruthenium
centres. With the verdazyl bridging two electron-poor Ru(hfac)2 fragments, the spin is
ligand-based and best described as RuII−vd•−RuII. Like the analogous mononuclear
complexes, the dinuclear complexes were each isolated in their other accessible oxidation
states. / Graduate / 0485
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/4963 |
| Date | 27 September 2013 |
| Creators | McKinnon, Stephen David James |
| Contributors | Hicks, Robin Gary |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Rights | Available to the World Wide Web |
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