Date of Award

1992

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Andrew W. Maverick

Abstract

The solution photophysics and photoredox reactions of several Mo$\sp{\rm III}$ and Mo$\sp{\rm V}$ complexes have been studied. Acetonitrile solutions of (Me$\sb3$ (9) aneN$\sb3$)MoX$\sb3$ (X = Cl, Br, I; Me$\sb3$ (9) aneN$\sb3$ = 1,4,7-trimethyl-1,4,7-triazacyclononane) are phosphorescent at room temperature, with the following emission maxima, lifetimes, and quantum yields: X = Cl, 1120 nm, 1.0 $\mu$s, and 6.1 $\times$ 10$\sp{-5}$; X = Br, 1130 nm, 800 ns, and 9.6 $\times$ 10$\sp{-5}$; X = I, 1160 nm, 400 ns, and 1.2 $\times$ 10$\sp{-4}$. HB(Me$\sb2$pz)$\sb3$MoCl$\sb3$ (Me$\sb2$pz = 3,5-dimethylpyrazole), (Me$\sb3$ (9) aneN$\sb3$)WCl$\sb3$ and mer-MoCl$\sb3$(pyridine)$\sb3$ phosphoresce more weakly. All three molybdenum-Me$\sb3$ (9) aneN$\sb3$ complexes undergo reversible one-electron photooxidation in the presence of acceptors such as tetracyanoethylene (TCNE) and 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil). (Me$\sb3$ (9) aneN$\sb3$)MoX$\sb3$ (X = Br, I) is photooxidized irreversibly to ((Me$\sb3$ (9) aneN$\sb3$)Mo$\sp{\rm IV}$X$\sb3$) $\sp+$ by C(NO$\sb2)\sb4$ in CH$\sb3$CN. In CH$\sb3$CN-H$\sb2$O (1:1 v/v), photoinitiated two-electron oxidation occurs: Mo$\sp{\rm IV}$ is also the initial product, but it disproportionates to form ((Me$\sb3$ (9) aneN$\sb3$)Mo$\sp{\rm V}$OX$\sb2$) $\sp+$. Acetonitrile solutions of Mo$\sp{\rm V}$OCl$\sb4$(CH$\sb3$CN)$\sp-$ and Mo$\sp{\rm V}$OBr$\sb4$(CH$\sb3$CN)$\sp-$, and CH$\sb2$Cl$\sb2$ solutions of Mo$\sp{\rm V}$OCl$\sb4$(H$\sb2$O)$\sp-$ and Mo$\sp{\rm V}$OBr$\sb4$(H$\sb2$O)$\sp-$, fluoresce at room temperature with maxima in the 900-950 nm range and the following excited-state lifetimes (and quantum yields): 100 ns (4 $\times$ 10$\sp{-4}$); 40 ns (1 $\times$ 10$\sp{-4}$); 60 ns (9 $\times$ 10$\sp{-5}$); and 30 ns (3 $\times$ 10$\sp{-5}$) respectively. ((Me$\sb3$ (9) aneN3)Mo$\sp{\rm V}$OBr2) $\sp+$, ((Me$\sb3$ (9) aneN$\sb3$)Mo$\sp{\rm V}$OI$\sb2$) $\sp+$, HB(Me$\sb2$pz)$\sb3$Mo$\sp{\rm V}$Cl$\sb2$ and ((Me$\sb3$ (9) aneN$\sb3$)W$\sp{\rm V}$OCl$\sb2$) $\sp+$ fluoresce more weakly in solution at room temperature. Mo$\sp{\rm V}$OCl$\sb4$(CH$\sb3$CN)$\sp-$ and Mo$\sp{\rm V}$OBr$\sb4$(CH$\sb3$CN)$\sp-$ are reversibly photooxidized in CH$\sb3$CN solution by TCNE and chloranil. The crystal structure of (BV) (MoOBr$\sb4$(H$\sb2$O)) Br$\cdot$CH$\sb3$CN has been determined by single crystal X-ray crystallography. Crystals of (BV) (MoOBr$\sb4$(H$\sb2$O)) Br$\cdot$CH$\sb3$CN are triclinic, space group P l. The compound luminesces in the solid state at room temperature. The luminescence of MoOBr$\sb4$(H$\sb2$O)$\sp-$ is not significantly quenched by the BV$\sp{2+}$ electron acceptors in the solid state, in spite of the thermodynamic favorability of the quenching process.

Pages

106

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