ABSTRACT THE IMPACT OF LIGAND DESIGN ON THE COORDINATION CHEMISTRY

AND PROPERTIES OF METAL SCORPIONATE COMPLEXES.

Chengeto Gwengo, BSc. (Hons.) Chemistry

Marquette University, 2009

The synthesis and coordination chemistry of new classes of scorpionate ligands are discussed, with the goal to discern the impact of steric and electronic modulation on the coordination chemistry and properties of metal scorpionates. The scorpionate ligands were functionalized by adding bulkier alkyl substituents at selected positions of the heterocycles rings, substituting pyrazoles with other heterocycles, replacing hydrogen at the back position of boron with aromatic groups in tris(pyrazolyl)borates or even by designing new classes of ligands altogether. We also looked at the prospect for designing dinucleating ligand derivatives by linking two ligand systems with p-xylene and butyne spacers. Several solution and solid state structural methods (Elemental analysis,

Mössbauer, IR, ESI-Mass spectroscopy, UV-Vis, NMR, Voltammetry, X-ray diffraction analysis) have been applied to distinguish between the different coordination modes and properties of metal complexes.

The synthesis, structures and the coordination chemistry of a series of iron (II) and iron

(III) scorpionates based on third generation para-

x - trimethylsilylphenyltris(pyrazolyl)borates, [p-Me3SiC6H4B(pz )3] are presented. The influence of pyrazolyl substituents on the spin state of iron (II) and iron (III) complexes was observed. The spin crossover behavior both in solution and in the solid state was

1 examined by magnetic susceptibility measurements, X-ray crystallography and electrochemical measurements. The donor-acceptor chemistry of para- trimethylsilylphenyltris(pyrazolyl)borates in an electrochromic device, using an electrical input as an external stimulus for electron transfer will be described. The pi-stacking interactions in Fe[tBu5HBCB(pz)3]2, with hexa-peri-hexabenzocoronenes (HBCs) tethered at the back of boron, were responsible for the unique spin characteristics of

Fe[tBu5HBCB(pz)3]2.

The supramolecular structures and solution characterization of alkali metal salts of the

- Janus scorpionate [HB(mtda)3] containing mercaptothiadiazolyls (mtda) heterocycles rings with both hard nitrogen and soft sulfur donors are described. Key structural parameters possibly facilitating the solid state assembly and solution properties are also described. In addition, the Janus scorpionate ligand exhibits extraordinary coordination capacity and versatility binding from two to five metal cations as demonstrated by its

Me - thallium (I) salt. The second generation Janus scorpionate ligand [HB(mtda )3] containing methyl-mercaptothiadiazolyl (mtdaMe) heterocyclic rings have been prepared.

The effect of methyl substitution versus the unsubstituted first generation Janus scorpionate on the spin state of iron (II) complexes has been studied structurally by

Mossbauer spectroscopy.

Motivated by the chemistry of the first and second generation Janus scorpionates, we

R synthesized the tris(thioimiadzolyl)methane; HC(tim )3 [where tim is thioimiadzolyl group and R = Me, tBu] to explore their coordination chemistry. The Lewis acid catalyzed thiol (CS-tim) to thione (CN-tim) isomerizations will be explained. Silver (I)

2 complexes of tripodal tim ligands have been prepared; their solid state and solution properties have been investigated by spectroscopic methods.

The new tetrakis(pyrazolyl)lutidine (pz4lut) ligands provided a versatile platform for interesting coordination chemistry. Owing to the multinucleating capability of pz4lut ligands, bimetallic silver (I) complexes with ligand binding in a bridging mode were synthesized. The adaptation of the silver complexes to the steric interaction of methyl groups at different positions of pyrazole was observed. The synthesis and characterization of manganese (I) and manganese (II) complexes with different coordination modes was successfully achieved. The influence of the nature of the counter anion on photo- oxidative decarbonylation of tricarbonyl manganese (I) products will be explored. A

5 x series of [κ -LMn(X)](OSO2CF3)n where L = pz 4lut or pz4Et2lut and n = 1 if X =

CF3SO3 or n = 2 if X = H2O were prepared and characterized. These complexes give unstable high oxidation state compounds on oxidation.

Finally, a brief introduction to bridged ligand systems with a potential for synthesis of bimetallic complexes will be discussed. Dinuclear iron (II) complexes of bridged pz4lut ligands were synthesized and partially characterized by cyclic voltammetry and electronic absorption spectroscopy and the properties of these complexes were compared with those of their mononuclear analogues. The use of the flexible hexyl spacer gave rise to the cross-bridged pz4hexyllut ligand, where the hexyl group is connected to the methine carbon atoms of the same pz4lut ligand. The iron (II) complex of the pz4hexyllut has been synthesized and characterized.

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