Open Access Dissertation
Date of Award
Charles H. Winter
A series of heavy alkaline earth metal tetrazolate complexes has been synthesized that contain metal ions saturated by aqua ligands. Tetrazolates with small ring-core carbon substituents favor formation of two dimensional polymers with u3-coordination of the tetrazolate to the metal centers. Tetrazolates with bulkier groups block coordination to the 1- and 4-nitrogen atoms, resulting in monomer formation. The first example of a trihydro(tetrazolyl)borate was prepared, and its bonding is heavily influenced by the basic BH3 moiety. 18-Crown-6 adducts of dihydrobis(tetrazolyl)borate complexes have been prepared that contain B-N bonding to the 2-nitrogen atoms, due to bulky ring-core atom substituents. A series of alkali metal hydrotris(tetrazolyl)borate complexes has been prepared by closely monitoring the reactions by electrospray ionization-mass spectrometry. The lithium hydrotris(tetrazolyl)borate complex contains k3-N,N,N bonding that is analgous to the bonding mode of hydrotris(pyrazolyl)borate ligands. The 18-crown-6 adducts of the sodium and potassium hydrotris(tetrazolyl)borate salts adopt n2-N,N and k2-N,H coordination modes, respectively, due to steric hindrances between the 18-crown-6 and hydrotris(tetrazolyl)borate ligands. The bonding modes of the hydrotris(tetrazolyl)borate complexes are stabilized by many hydrogen-bonding and dihydrogen-bonding contacts between the hydrotris(tetrazolyl)borate ligand and the ancillary ligand on the metal center. A series of poly(pyrazolyl)aluminate complexes containing aluminum-hydrogen bonds has been prepared, and these complexes exhibit similar coordination modes to their poly(pyrazolyl)borate analogues. Pyrazolyl exchange processes occur at room temperature in solution due to the weak Al-N and Al-H bonds. Salt metathesis of the new complexes with metal(II) halides yielded ligand, hydride, or pyrazolate transfer, depending on the metal and reaction conditions. The reactivity of 5-substituted tetrazoles with lithium aluminum hydride was investigated in an attempt to prepare tetrakis(tetrazolyl)aluminate salts at low temperatures to avoid thermal decomposition of the parent tetrazoles. The reactions yielded complex reaction mixtures that were only soluble in polar solvents. A lithium tetrazolate was isolated from one of the reaction mixtures, which may be due to an equilibrium between the lithium tetrakis(tetrazolyl)aluminate complex and lithium and aluminum tetrazolate complexes in solution.
All tetrazolate and poly(tetrazolyl)borate complexes presented herein are thermally stable above 200 °C, are insensitive to shock, friction, and electrical discharge, and can be handled safely. The tetrazolate complexes described herein deflagrate or explode upon exposure to a flame, and therefore may serve as secondary energetic materials or colorants in pyrotechnics. The poly(tetrazolyl)borate complexes are insensitive to the flame test, with the exception of the lithium hydrotris(tetrazolyl)borate, which explodes upon exposure to a flame.
Snyder, Christopher James, "Synthesis And Characterization Of Metal Complexes Containing Tetrazolate, Poly(tetrazolyl)borate, And Poly(azolyl)aluminate Ligands As High Energy Density Materials" (2013). Wayne State University Dissertations. 702.