12-metallocrown-4: A structural and functional inorganic analogue of 12-C-4.

Metallacrowns are a class of inorganic molecular recognition agents which are analogous to crown ethers. The metallacrown analogy replaces the methylene units of crowns with transition metal-nitrogen linkages which leads to molecules with strong visible absorption spectra, paramagnetism and redox activity. Generalizing the metallacrown analogy as a synthetic protocol for the preparation of multinuclear complexes required metallacrowns synthesized with various (1) organic ligands, (2) ring metals, (3) core metals and (4) bound anions in the predicted structural motifs. Chapter II discusses the synthesis of copper 12-metallacrown-4's from novel hydroxamic acid ligands, e.g. anthranilic hydroxamic acid, which alter the donor atoms and the peripheral organic architecture. Vanadium, iron, manganese, copper and gallium metallacrowns are synthesized from salicylhydroxamic acid derivatives. Alkali metal:halide complexes of the manganese 12-metallacrown-4 allow for comparison of the structural features influencing joint cation/anion binding. Comparisons of metallacrown, crown ether, phthalocyanine and porphyrin structures are made. Chapter III defines the solution integrity and dynamics of the metallacrowns using electrospray ionization mass spectrometry, NMR spectroscopy ($\sp1$H, $\sp{51}$V), UV-visible spectroscopy and EXAFS. Analysis of all the data proves that the majority of metallacrowns are stable in methanol, acetonitrile and DMF. NMR demonstrates both halides and cations remain bound to (12-MC$\sb{\rm Mn(III)N(shi)}$-4) in solution. Ligand exchange studies between metallacrowns show that several of the metallacrowns are dynamic in methanol (the fastest rate is k = 2.48 $\pm$.07 hr$\sp{-1}$) but all are inert in acetonitrile and DMF. Chapter IV establishes the metallacrown's functional analogy to crown ethers. Cation affinity $\rm (Li\sp+ > Na\sp+ > K\sp+$) and anion affinity $\rm (Cl\sp- > Br\sp- > I\sb3\sp-$) of (12-MC$\sb{\rm Mn(III)N(shi)}$-4) were established quantitatively. Anion binding constants, e.g. log K$\sbsp{1}{\rm Br\sp-} = 3.2$ M$\sp{-1}$, were established by NMR. Crown ethers provided the cation binding constants of the metallacrowns. Potassium binds poorest of the alkali metals studied, log K$\sbsp{2}{\rm K\sp+(Br\sp-)}$ = 3.2, and binding of chloride increases the cation affinity, log K$\sbsp{2}{\rm K\sp+(Cl\sp-)}$ = 6.4. Lithium binds strongest, log K$\sbsp{1}{\rm Li\sp+} \approx 15$. Manganese quantitatively displaces all the alkali metal:halide salts complexes studied when acetate is present. The joint recognition of cation and anion pairs is unique in molecular recognition chemistry.PhDChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/104304/1/9513363.pdfDescription of 9513363.pdf : Restricted to UM users only