Computational Studies Of Small Inorganic Molecules And Synthesis Of Coinage Metal Pyrazolate Complexes

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2008-04-22T02:41:27Z

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Chemistry & Biochemistry

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The first part of this dissertation describes computational studies of alkaline earth metal pnictides such as [M3X2] (M = Ca, Mg and X = N, P, As) and [Ca6X4] (X =P, As). These small inorganic systems are of great interest due to the lack of geometrical and electronic structure information. The global minimum for each system was searched for by ab initio methods. For all geometries, single point energies were calculated at highlevels such as CCSD(T) and QCISD(T) using several basis sets for Ca, 6-311G* for Mg and 6-311+G* for N, P, and As. These systems were sensitive to the Ca basis set as well as electron correlation effects; hence, we performed detailed bench mark calculations. The [Ca6P4] and [Ca6As4] systems are less sensitive to the basis sets and the methods. We found two minimum energy structures for the [M3X2] systems except for the nitride system. The singlet state structures had D3h symmetry. Interestingly, the triplet state structure has been found to be a Jahn-Teller distorted molecule with C2v symmetry. All the [M3X2] systems have trigonal bipyramidal geometry. NBO analyses were performed to understand the electronic structures. In the second part we discussed the π-acid/base complexes of coinage metal trinuclear systems and arenes. We discovered that the acidic [{3,5-(CF3)2Pz}M]3, (M = Ag, Au) and [{3-(C3F7)-5-(But)2Pz}Ag]3 form a variety of sandwich molecules and supramolecular stacks with aromatic π systems. The basic stacking pattern depends on the solvent, arene, metal atom and substituents on the pyrazole ring. The distance between the trimer and the arene system indicate moderately strong π-acid/base interactions. The structures were characterized using x-ray crystallography, elemental analysis and NMR. Some of the sandwiched complexes are luminescent and the emission is ligand based. The trinuclear systems were studied for reactivity with P and N based secondary ligands. We discovered that trimers form mostly polymers with N based ligands. In order to interpret formation of polymeric complexes, we studied the molecular weights of [{3,5-(CF3)2Pz}Ag]3 at different concentrations using vapor pressure osmometry. We discovered that this system has different morphologies at different concentrations. We have discovered different structural patters using different tertiary phosphine ligands. We synthesized series of dinuclear complexes using bis(diphenylphosphinomethane).

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