Date of Graduation

Fall 2022

Degree

Master of Science in Chemistry

Department

Chemistry and Biochemistry

Committee Chair

Nikolay Gerasimchuk

Abstract

A new series of Pb(II) cyanoximates were synthesized and characterized by elemental analysis (C, H, N, S), IR spectroscopy, thermal analysis, and X-ray crystallography. The goal was to synthesize compounds with a PbL2 (L= selected known chelating cyanoximes) composition for use as potential new non-linear optical (NLO) materials, specifically second harmonic generators (SHG), which must belong to non-centrosymmetric space groups. A desktop procedure using Pb2+ is chosen due to its typically active 6s2 lone pair of electrons, which are known to distort central polyhedra. A 1:2 ratio of Pb(II) to ligand were used to synthesize bulk products and grow crystals for structural determination. Bulk product resulted with 3 compounds with the desired PbL2 structure but unable to confirm non-centrosymmetric space group due to lack of single crystals for XRD analysis. Thus, crystal growth using a variety of methods became the main objective, although this proved difficult due to hydrolysis occurring on both the lead and ligand sides. Lead hydrolysis appears to dominate, as those fragments are present in most crystal structures. Overall, 30 promising crystals were analyzed resulting with six different lead/ ligand determined structures. The H(2PCO) ligand was the most successful system with three different structures. Crystal data revealed dimeric structure of Pb{(H2PCO)(2PCO)2 · H2O} with one 2PCO- anion in cis-syn orientation, which has never been seen before with this ligand, forming 6-member ring in chelation while acting as a μ-2 bridge. The only structure determined exclusively containing lead/ligand was Pb{(H2PCO)2(2PCO)2}and the only compound without active lone pair of electrons. Other structures determined were Pb3(2PCO)4(NO3)2, Pb3(OH)(NO3)(DCO)4, Pb4(OH)3(NO3)2(PiPCO)3(H2O), and one hydrolysis product from H(ECO) reaction, K2[Pb3(AACO)4(H2O)]2. The Pb(II) lead centers in crystal growth had high coordination with multiple lead centers, ligands acting as bridges, and invasion of spectator ions resulting in much more complex structures than desired, all belonging to centrosymmetric space groups. Unexpected results showed three products have properties of high-energy compounds, which violently decompose with release of significant heat and kinetic energy. Compared to known high-energy compounds these have high potential for use as heat-triggered actuators.

Keywords

lead(II) compounds, synthesis cyanoximes, X-ray analysis, crystal growth, hydrolysis reactions, high-energy compounds, thermal analysis

Subject Categories

Inorganic Chemistry

Copyright

© Patricia McDaniel

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