The Coordination Chemistry of the Rhodizonate Dianion and Its Decomposition Products

Authors

Joshua A. Silverman, Florida International UniversityFollow

Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

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First Advisor's Name

Konstantinos Kavallieratos

First Advisor's Committee Title

Committee chair

Second Advisor's Name

Raphael Raptis

Second Advisor's Committee Title

Committee member

Third Advisor's Name

Christopher Dares

Third Advisor's Committee Title

Committee member

Fourth Advisor's Name

Watson Lees

Fourth Advisor's Committee Title

Committee member

Fifth Advisor's Name

Werner Boeglin

Fifth Advisor's Committee Title

Committee member

Keywords

chemistry, rhodizonate, croconate, oxalate

Date of Defense

6-29-2021

Abstract

The rhodizonate dianion is of importance for forensic testing, specifically with regard to the sodium rhodizonate test for lead in gunpowder residues. In an effort to understand this test from a chemical perspective, the coordination of rhodizonate and its decomposition products, croconate and oxalate, with several metals has been investigated with a variety of structural and spectroscopic methods.

FT-IR data of the three sequential steps of the sodium rhodizonate test show coordination between Pb(II) atoms, tartrate anions, and rhodizonate dianions, with the tartrate being substituted for Cl^- once a 5% HCl solution is added to produce the confirmatory blue-purple color for Pb. XPS data confirms the coordination of Cl^- to Pb(II) with a shift from the major XPS peak of the Pb 4f_7/2 peak from 138.6 eV to 139.0 eV. UV-Vis titrations show that Pb(II) and rhodizonate bind in a 1:1 ratio in water/ethanol (50/50 by volume). This solvent system was essential for generating these results, as in pure water, the formed Pb-rhodizonate complex immediately precipitates.

Rhodizonate was also shown to complex with lanthanides. UV-Vis titrations show that rhodizonate coordinates to lanthanides in 1:1 ratio in water/ethanol (50/50 by volume). However, rhodizonate has higher affinity for Pb(II) over several Ln(III).

Metal-rhodizonates with N-donating co-ligands such as 1,10-phenanthroline, 2,2’-bipyridine, and imidazole, were also shown to coordinate to toxic metals, such as Hg(II) in a 1:1 metal-rhodizonate/co-ligand ratio in water/ethanol (50/50 by volume), regardless of whether the co-ligand was added to a solution of metal-rhodizonate, or the metal was added to a solution of rhodizonate and co-ligand.

Dilute solutions (~10^-5 M) of sodium rhodizonate, which are suitable for UV-Vis spectroscopic work will typically decompose and lose their characteristic orange color in about 2 h, though full decomposition into croconate takes upwards of one week. We have now shown that by dissolving rhodizonate in water/ethanol (50/50 by volume), the stability of rhodizonate in solution is extended by several hours, allowing for accurate UV-Vis spectroscopic measurements, titration studies, and determination of binding constants.

Crystals of the five-member croconate, a decomposition product of rhodizonate, with Pb(II) and Cd(II) show marked differences. Pb(II)-croconate crystals feature 3D-layers of alternating Pb(II) and croconate, while Cd(II)-croconate crystals feature 1D-layers of alternating Cd(II) and croconate held together through a hydrogen bonding network. Metal-rhodizonate solutions left over longer times will further decompose into oxalates, which can then form, 3D metal-oxalate frameworks. The 3D structures are unique among metal oxalates, forming large pores, in contrast to 1D and 2D metal-oxalates previously reported in the literature.

Identifier

FIDC010234

Previously Published In

Silverman, J. A., Mathivathanan, L., Govor, E. V., Raptis, R. G., Kavallieratos, K., Acta Cryst C, 2019, 75, 935-940. https://doi.org/10.1107/S2053229619007277.

Recommended Citation

Silverman, Joshua A., "The Coordination Chemistry of the Rhodizonate Dianion and Its Decomposition Products" (2021). FIU Electronic Theses and Dissertations. 4714.
https://digitalcommons.fiu.edu/etd/4714