Sarah K. Gibbons

Uranium (U) is a radiologically and chemically toxic element that occurs naturally in water, soil, and rock at generally low levels. However, anthropogenic uranium can also leach into groundwater sources due to mining, ore refining, and improper nuclear waste management. Over the last few decades, various methods for measuring uranium have emerged; however, most of these techniques require skilled scientists to run samples on expensive instrumentation for detection or require the pretreatment of samples in complex procedures. In this work, a Schiff base ligand (P1) is used to develop a simple spectrophotometric method for measuring the concentration of uranium (VI) with an accurate and affordable light-emitting diode (LED) spectrophotometer. A test for a higher-order polynomial relationship was used to objectively determine the calibration data’s linearity. This test was done with a Python program on a Raspberry Pi computer that captured the spectrophotometer’s calibration and sample measurement data.

2-(((2,7-Dihydroxynaphthalen-1-yl)methylene)amino)-3′,6′-bis(ethylamino)-2′,7′-dimethylspiro[isoindoline-1,9′-xanthen]-3-one was synthesized using Rhodamine 6G hydrazide (prepared using literature methods) and commercially available 2,7-dihydroxynaphthalene-1-carbaldehyde via imine condensation. Structural characterization was performed using FT-IR, ¹H-NMR, ¹³C-NMR, X-ray, and HRMS. This Schiff base shows promise as a ligand for the colorimetric analysis of uranium in water.

Diastereoselective coordination of racemic secondary phosphines (PHRR′) to Cu(I) precursors containing chiral bis(phosphines) (diphos*) was explored as a potential route to P-stereogenic phosphido complexes. Reaction of [Cu(NCMe)₄][PF₆] with chiral bis(phospholanes) gave [Cu(diphos*)₂][PF₆] (diphos* = (R,R)-Me-DuPhos (1), (R,R)-Et-DuPhos (2), or (R,R)-Me-FerroLANE) (3)) or the mono(chelates) [Cu(diphos*)(NCMe)_n][PF₆] (diphos* = (R,R)-i-Pr-DuPhos, n = 2 (4); diphos* = (R,R)-Me-FerroLANE, n = 1 (5)). Treatment of [Cu(NCMe)₄][PF₆] with diphos* and PHMe(Is) (Is = 2,4,6-(i-Pr)₃C₆H₂) gave mixtures of diastereomers of [Cu((R,R)-i-Pr-DuPhos)(PHMe(Is))(NCMe)][PF₆] (6) and [Cu((R,R)-Me-FerroLANE)(PHMe(Is))][PF₆] (7); two of the three expected isomers of the bis(secondary phosphine) complexes [Cu((R,R)-i-Pr-DuPhos)(PhHP(CH₂)_nPHPh)][PF₆] (n = 2 (8); n = 3 (9)) were formed preferentially in related reactions. Reaction of the halide-bridged dimers [Cu((R,R)-i-Pr-DuPhos)(X)]₂ or [Cu((R,R)-Me-FerroLANE)(I)]₂ with PHMe(Is) gave the labile adducts Cu((R,R)-i-Pr-DuPhos)(PHMe(Is))(X) (X = Cl (10), Br (11), I (12)) and Cu((R,R)-Me-FerroLANE)(PHMe(Is))(I) (13). Complexes 1, 6, and 8–11 were structurally characterized by X-ray crystallography. Variable temperature NMR studies of 6 and 8 showed that the secondary phosphine ligands underwent reversible dissociation. Deprotonation of 6 or 7 generated the P-stereogenic phosphido complexes Cu(diphos*)(PMeIs) (diphos* = (R,R)-i-Pr-DuPhos (14) or (R,R)-Me-FerroLANE) (17)), observed by ³¹P NMR spectroscopy, but decomposition also occurred. Density functional theory calculations were used to characterize the diastereomers of thermally unstable 17 and the inversion barrier in a model copper-phosphido complex. These observations provided structure–property relationships which may be useful in developing catalytic asymmetric reactions involving secondary phosphines and P-stereogenic copper phosphido intermediates.

For investigation of structure–property relationships in copper phosphine halide complexes, treatment of copper(I) halides with chiral bis(phosphines) gave dinuclear [Cu((R,R)-i-Pr-DuPhos)(μ-X)]₂ [X = I (1), Br (2), Cl (3)], [Cu(μ-((R,R)-Me-FerroLANE)(μ-I)]₂ (5), and [Cu((S,S)-Et-FerroTANE)(I)]₂ (6), pentanuclear cluster Cu₅I₅((S,S)-Et-FerroTANE)₃ (7), and the monomeric Josiphos complexes Cu((R,S)-CyPF-t-Bu)(I) (8) and Cu((R,S)-PPF-t-Bu)(I) (9); 1–3, 5, and 7–9 were structurally characterized by X-ray crystallography. Treatment of iodide 1 with AgF gave [Cu((R,R)-i-Pr-DuPhos)(μ-F)]₂ (4). DuPhos complexes 1–4 emitted yellow-green light upon UV irradiation at room temperature in the solid state. This process was studied by low-temperature emission spectroscopy and density functional theory (DFT) calculations, which assigned the luminescence to (M + X)LCT (Cu₂X₂ to DuPhos aryl) excited states. Including Grimme’s dispersion corrections in the DFT calculations (B3LYP-D3) gave significantly shorter Cu–Cu distances than those obtained using B3LYP, with the nondispersion-corrected calculations better matching the crystallographic data; other intramolecular metrics are better reproduced using B3LYP-D3. A discussion of the factors leading to this unusual observation is presented.

Synthetic, structural, spectroscopic and aging studies conclusively show that the main colorant of historical iron gall ink (IGI) is an amorphous form of Fe(III) gallate • x H₂O (x = ~1.5 – 3.2). Comparisons between experimental samples and historical documents, including an 18th century hand-written manuscript by George Washington, by IR and Raman spec-troscopy, XRD, X-ray photoelectron spectroscopy and Mössbauer spectroscopy confirm the relationship between the model and authentic samples. These studies settle controversy in the cultural heritage field, where an alternative structure for the Fe(III) gallate has been commonly cited.