Photophysical and photochemical properties of oxo and nitrido complexes of osmium(VI)

by Lam, Hiu-fung

(Uncorrected OCR) Abstract of thesis entitled

PHOTOPHYSICAL AND PHOTOCHEMICAL PROPERTIES OF OXO AND NITRIDO COMPLEXES OF OSMIUM(VI)

submitted by Lam Hiu Fuog

for the degree of Master of Philosophy at the University of Hong Kong

in September, 2001

The complexes [P14Ash[OsN(CN)s] and [P14Ash[OsN(CN)4CI] were synthesized and their x-ray structures determined. The Os=N distance of 1.54(1)A for [OsN(CN)sClf is larger than that of 1.73(1)A for [OsN(CN)sf. The spectroscopic and photochemical properties of [OsN(CN)st and [OsN(CNhClf were studied. The emission of [P14Ash[OsN(CN)4CI] is at a lower energy than that of [P14Ash[OsN(CN)sJ. The [OsN(me4enh(OHz)](CF3S03h [me4en = 2,3-dimethyl-2,3-diaminobutane] complex was prepared by reacting [OsN(me4en)zCI]Ch with trifluoromethanesulfonic acid, Its crystal structure shows a weakly coordinated OHz molecule trans to the Os=N unit.

Time-resolved absorption spectroscopy was employed to study the absorption spectra of the 3[(dxy),(dxz, dyz)] states ofnitridoosmium(VI) complexes containing aromatic diimine or cyanide ligands.

Nitrido coupling reactions were studied and the products obtained were characterized. Addition of Zn(Hg) to [OsN(me4enh(OHz)](CF3S03h in acetonitrile or dichloromethane solution led to formation of Il-nitrido species of {[Os(me4en-HhhC ).l-N)}(CF3S03h. The crystal structure of ([Os(me4enH)2hC Il-N)}(CF3S03)3 shows a linear Os-N-Os unit with the Os-N distance being 1.814(6) A. The {[Os(me4en-H)212( Il-N)}(CF3S03)3 is diamagnetic and a Os v -N-Os v formation is suggested.

A senes of dioxoosmium(VI) complexes were prepared and their spectroscopic and photochemical properties were studied. Low temperature emission and excitation spectra and theoretical calculations were employed to study the 3[(dxy),(dxz, dyz)] excited state of [Os02(CN)4f. The P1t(Oz-) to Os(VI) charge transfer excited state, rather than the d-d one, is responsible for lightinduced organic oxidations by trans-dioxoosmium(VI).

A senes of dicyanoosmium(II) complexes were prepared and their spectroscopic properties were studied.

Addition of a metal ion to the dicyanoosmium(II) complex leads to enhancement of the emission intensity and shifting of emission wavelength to lower energy. The x-ray crystal structure of {[Os(PPh3)2(phen)]().lCN)[Zn(N03)Z]}OO was determined.