Solid State NMR Studies of Lead(II) Thiourea Materials
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0984-MM07-20
Solid State NMR Studies of Lead(II) Thiourea Materials Cecil Dybowski1, Alicia Glatfelter1, Shi Bai1, D. Martinez2, S. Segarra2, and Dale L. Perry2 1 Department of Chemistry and Biochemistry, University of Delaware, Newark, DE, 19716 2 Lawrence Berkeley National Laboratory, University of California, MS 70A-1150, Berkeley, CA, 94720
ABSTRACT Solid-state 13C and 207Pb NMR have been used to characterize a series of lead(II) ion complexes containing thiourea – widely used in materials science – as the organic complexing molecule. NMR data for the complexes have been measured and discussed with respect to the reported structures for the complexes.
INTRODUCTION Thiourea is extensively used in materials science. It can be the basis of the materials themselves, or it may play a role in the syntheses of materials. For example, thiourea-based materials containing zinc and cadmium are used as electro-optic modulators,1 while transition-metal-ion-doped urea materials have been used as ferroelectric materials.2 Thiourea has also been used in inclusion complexes of organometallics as nonlinear optical materials,3 a synthetic template for the synthesis of copper(I)-doped ZnS nanoparticles,4 and for the synthesis of metal sulfide semiconductor nanocrystallites.5 The present work describes 13C and 207Pb NMR investigations of a series of lead(II) halides that are complexed with thiourea. The spectral parameters for the compounds are given, with a discussion of their dependence on the state of co-ordination. The changes in NMR parameters from the complexed state to the uncomplexed state are indicators of structural and electronic changes in the materials.
EXPERIMENTAL Chemicals. Lead(II) halides were purchased as reagent-grade chemical (Alfa Chemicals), while reagent-grade thiourea was purchased from Aldrich Chemical. All were used as received without further purification. Synthesis. The synthesis of thiourea complexes followed a procedure due to Wharf. PbCl2 was dissolved in a boiling solution of thiourea and water. Filtration of the hot solution followed by slow cooling of the filtrate gave the bis-adduct, PbCl2(thiourea)2. Using the same procedure with PbBr2 also gave the bis-adduct, PbBr2(thiourea)2. Carrying the PbBr2/thiourea solution through similar procedures, but with fast cooling, yielded the mono-adduct, PbBr2(thiourea). PbI2 was reacted with 6
thiourea while stirring for two hours and filtered hot to produce the mono-adduct, PbI2(thiourea). The purity of these complexes has been checked by melting points as reported in the literature.7 207
Pb NMR Analyses of Thiourea Complexes. Lead spectra were obtained with a Bruker MSL 300 NMR spectrometer at a nominal frequency of 62.601 MHz, using a spin-echo technique on a standard Bruker CP-MAS probe. All 207Pb spectra reported are of static powders. All shifts are reported relative to Pb(CH3)4 (TML). Solid Pb(NO3)2 was used as a secondary reference, defined as -3491.6 ppm relative to TML at 295 K.8 The shifts were determined by fitting the experimental data to a
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