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Characterization of a platinum-substituted keggin anion and studies of robust, hydrogen-bonded polyanion aggregates

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Title: Characterization of a platinum-substituted keggin anion and studies of robust, hydrogen-bonded polyanion aggregates
Author(s): Goloboy, James
Director of Research: Klemperer, Walter
Doctoral Committee Chair(s): Klemperer, Walter
Doctoral Committee Member(s): Rauchfuss, Thomas B.; Zimmerman, Steven; Murphy, Catherine
Department / Program: Chemistry
Discipline: Chemistry
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: Ph.D.
Genre: Dissertation
Subject(s): chemistry inorganic chemistry keggin polyoxometalates polyoxoanions hydrogen bonding platinum
Abstract: Solution and solid-state studies of platinotungstate and platinomolybdate heteropolyanions were carried out. Salts of the Keggin-type -SiPtW11O406- anion (1) were prepared through the reaction of K8SiW11O39.13H2O with K2Pt(OH)6 and acidification of the reaction solution to pH 4 with HNO3. Infrared spectra indicated cocrystallization of tetra-n-butylammonium salts of the SiW12O404- anion with the platinum substituted derivative, and this difficulty was overcome through an initial precipitation with tetramethylammonium chloride and extraction of the precipitate with water in order to remove insoluble [(CH3)4N]4SiW12O40. A single-crystal X-Ray diffraction study of the tetra-n-butylammonium salt allowed for identification of a Keggin tetraanion in the solid state. Incorporation of a single Pt(IV) atom in 1was demonstrated unambiguously by observation of 195Pt-183W spin-spin coupling in 195Pt and 183W NMR spectra of the cesium salt, as well as observation in the 183W NMR spectrum of six peaks having relative intensities consistent with structure 1. These observations plus elemental analysis identified the tetra-n-butylammonium salt as [n-C4H9)4N]4SiPtW11O40H2. The tetrameric platinomolybdate [(PtMo6O24)4H21(H5O2)2][(n-C4H9)4N]9 (H2TET TBA9) was prepared from the reaction of K2Pt(OH)6 with K2MoO4 and acidification of the reaction solution to pH 2.32 with HNO3. A single-crystal X-Ray diffraction study showed that the nearest-neighbor protonated (PtMo6O24)8- units were linked by seven hydrogen bonds. The 195Pt NMR spectrum of the tetramer showed two resonances of equal intensity, consistent with the resonances anticipated from the solid-state structure. The 1H NMR spectrum provided further evidence that the anion retained its hydrogen-bonded structure in solution. Variable temperature NMR and a 2D EXSY experiment allowed for partial assignment of the proton resonances in the 1H NMR spectrum. A cooperative hydrogen bonding effect was proposed to rationalize the stability of the hydrogen-bonded aggregate in solution. The DL configuration adopted by the tetramer was rationalized through a “proton exclusion” model. Reaction of the platinomolybdate tetramer with a large excess of triethylamine led to the formation of the analytically pure bulk platinomolybdate [(PtMo6O24)3H15][(C4H9)4N]6[(C2H5)3NH]3, (HTRI TBA6TEAH3). Crystallization of this material from acetonitrile/toluene gave a solvated salt of the [(PtMo6O24)3H16]8- (H2TRI) anion, while crystallization from acetonitrile/diethyl ether gave a salt of the [(PtMo6O24)3H14]10- (TRI) anion. It was therefore proposed that the bulk platinomolybdate trimer was in fact a mixture of H2TRI and TRI salts. The protonated (PtMo6O24)8- units of the trimeric anions were linked through the same seven hydrogen bond motif as in the tetramer. 1H NMR spectra of an H2TRI/HTRI mixture indicate that the trimers adopt the same D and L configurations observed in H2TET. The transformation of the tetramer to the trimer was monitored by 1H and 195Pt NMR titrations of H2TET with triethylamine in a hydrated 1:4 (v/v) CD3CN/CDCl3 solution, demonstrating that H2TET first dissociates to TET in solution, converts to H2TRI with the addition of triethylamine, and then to HTRI with the addition of further triethylamine. Addition of water to a solution of H2TET and five equivalents of water gave a 1H NMR spectrum consistent with that of a hydrogen-bonded platinomolybdate dimer.
Issue Date: 2011-05-25
URI: http://hdl.handle.net/2142/24106
Rights Information: Copyright 2011 James Goloboy
Date Available in IDEALS: 2011-05-25
Date Deposited: 2011-05
 

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