Senior Honors Projects, 2010-current

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

Date of Award

Spring 2014

Document Type

Thesis

Degree Name

Bachelor of Science (BS)

Department

Department of Chemistry and Biochemistry

Advisor(s)

Barbara A. Reisner

John W. Gilje

Thomas C. DeVore

Brycelyn M. Boardman

Abstract

Variations to synthetic conditions and reaction components were explored to understand the factors that influence framework assembly in monovalent metal-organic frameworks synthesized from the polydentate ligand hydrotris(1,2,4-triazolyl)borate, [BH(trz)3]-. The role of solvothermal conditions, monovalent metal counterion size, and covalent ligand substitution were studied. A[BH(trz)3] (A = Li, Na, K) were synthesized by reacting ABH4 with 1,2,4- triazole (Htrz) under reflux. K[BH(trz)3] was crystallized from acetonitrile in the monoclinic space group P21/c as a three-dimensional, nonporous framework with hex topology (a=9.2318(8) Å, b=7.5195(7) Å, c=15.6718(14) Å, α=γ=90°, β=103.5070(10)°). Li[BH(trz)3] was crystallized from acetonitrile in the orthorhombic space group Pbca as two-dimensional, corrugated sheets with fes topology (a=11.3790(5) Å, b=13.4027(6) Å, c=14.3289(6) Å, α= β=γ=90°). Cu[BH(trz)3] also adopts the fes topology and was crystallized via cation exchange between K[BH(trz)3] and CuI in isopropanol (a=11.2689(10) Å, b=13.3005(12) Å, c=14.5276(13) Å, α= β=γ=90°). Na[BH(trz)3]•C3H7NO was previously synthesized from N,N-dimethylformamide; it crystallizes in the pcu topology. A comparison of these materials suggests that cationic radius plays a significant role in directing framework assembly. Increasing the ionic radius of the metal increases the coordination number, and as a result, increases the number of exodentate nitrogen atoms that can coordinate the metal center. Increasing the number of exodentate nitrogen atoms that coordinate the metal center increased framework dimensionality. Li[BH(trz)3]•C3H8O crystallized from isopropanol was identified as a new crystalline polymorph in the Li[BH(trz)3] system. Spectroscopic and thermal analysis data suggest that the material contains an isopropanol of crystallization. For other monovalent cations, no other crystalline polymorphs were isolated from different solvents. This suggests that solvent may play a limited role in framework assembly. To investigate the impact of steric hindrance on framework assembly, K[BH(dmtrz)3] (dmtrz = 3,5-dimethyl-1,2,4-triazole) was synthesized. The synthesis of K[BH(dmtrz)3] will be discussed.

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