New structural insight for antimony(III)-tartrate

A Comprehensive Potentiometric Study of the Tartrate Complexes of Trivalent Arsenic, Antimony, and Bismuth in Aqueous Solution

The tartrate complexes of trivalent arsenic, antimony, and bismuth were studied potentiometrically. The existing, fragmentary data on the antimony/l-(+)-tartrate system were confirmed. Nine complexes of arsenic and bismuth with optically active, racemic, and meso-tartrate, as well as complexes of antimony with meso-tartrate, were newly identified, and their formation constants computed. Difficulties arising from the poor stability of the arsenic complexes and precipitation in the Sb(III)/meso-tartrate system were overcome by titrating at very high concentrations [As(III) systems] and using an auxiliary ligand [Sb(III) in the presence of catechol]. All data were obtained at 25.0 °C and at constant ionic strength [0.1 mol L^-1 for Sb(III) and Bi(III) complexes and 1 mol L^-1 for As(III) complexes]. Speciation diagrams of all systems at millimolar concentrations were computed on the basis of the newly obtained constants and the results discussed.

Detection of organic and inorganic gunshot residues from hands using complexing agents and LC-MS/MS

Gunshot residue (GSR) refers to a conglomerate consisting of both organic molecules (OGSR) and inorganic species (IGSR). Historically, forensic examiners have focused only on identifying the IGSR particles by their morphology and elemental composition. Nonetheless, modern ammunition formulations and challenges with the GSR transference (such as secondary and tertiary transfer) have driven research efforts for more comprehensive examinations, requiring alternative analytical techniques. This study proposes the use of LC-MS/MS for chromatographic separation and dual detection of inorganic and organic residues. The detection of both target species in the same sample increases the confidence that chemical profiles came from a gun's discharge instead of non-firearm-related sources. This strategy implements supramolecular molecules that complex with the IGSR species, allowing them to elute from the column towards the mass spectrometer while retaining isotopic ratios for quick and unambiguous identification. The macrocycle (18-crown-6-ether) complexes with lead and barium, while antimony complexes with a chelating agent (tartaric acid). The total analysis time for OGSR and IGSR in one sample is under 20 minutes. This manuscript expands from a previous proof-of-concept publication by improving figures of merit, increasing the target analytes, testing the method's feasibility through a more extensive set of authentic specimens collected from the hands of both shooters and non-shooters, and comparing performance with other analytical techniques such as ICP-MS, electrochemical methods and LIBS. The linear dynamic ranges (LDR) spread across the low ppb range for OGSR (0.3-200 ppb) and low ppm range (0.1-6.0 ppm) for IGSR. The method's accuracy increased overall when both organic and inorganic profiles were combined.

Low-Molecular-Weight Organic Acid Complexation Affects Antimony(III) Adsorption by Granular Ferric Hydroxide

Antimony(III) mobility in natural aquatic environments is generally enhanced by dissolved organic matter. Tartaric acid is often used to form complexes with and stabilize dissolved Sb(III) in adsorption studies. However, competition between such low-molecular-weight organic acid complexation and adsorption of Sb(III) has received little attention, which prompted us to measure Sb(III) adsorption by iron oxyhydroxide adsorbents commonly used in water treatment plants. Sb K-edge X-ray absorption fine structure (EXAFS) spectra gave Sb-O and Sb-Fe distances and coordinations compatible with a bidentate binuclear inner-sphere complex with trigonal Sb(O,OH)₃ polyhedra sharing corners with Fe(O,OH)₆ octahedra and a bidentate mononuclear inner-sphere complex but with Sb(O,OH)₄ tetrahedra at alkaline pH. Experimental batch titration data were fitted using the charge-distribution multisite surface complexation (CD-MUSIC) model, constrained by the EXAFS molecular level information and taking competitive effects by the organic ligand into consideration. The proportion adsorbed at acid to neutral pH decreased as the Sb(III) concentration increased. The CD-MUSIC adsorption model indicates that this was solely caused by strong competition from tartrate complexation in solution, which leads to adsorption constants higher than those derived without taking this competition into account. The adsorption model results allow for calculating a pe-pH predominance diagram using the USGS PhreePlot code. The study provides consistent surface complexation stability constants, allowing the new database to be used also to reliably model adsorption of toxic oxyanions in anoxic aqueous environments: for example, to accurately simulate competition between Sb(III) and As(III).

Stacking changes of KLi[Sb2(C4H2O6)2] homochiral layers mediated by interlayer solvent molecules

A new compound KLi[Sb2(C4H2O6)2]·4H2O, 1, was synthesized in single crystal form by slowly evaporating an aqueous solution of potassium antimony tartrate and lithium nitrate. The structure of 1 consists of homochiral layers of antimony tartrate dimers linked by LiO4 tetrahedra. The interlayer water molecules can be reversibly driven out by heating or exchanged by small alcohol molecules under ambient conditions, occurring via single-crystal to single-crystal transformations. To accommodate different interlayer molecules, the interlayer space is changed by adjusting the relative lateral shift of neighboring layers. A similar adjustment in the layer stacking also occurs in a structural phase transition caused by order-disorder transformation of the arrangement of interlayer methanol molecules at low temperature.

Synthesis and structural phase transitions of [Mg2Sb2(C4H2O6)2(H2O)8](ClO4)2·5H2O with complex homochiral chains

A new magnesium antimony tartrate perchlorate [Mg2Sb2(C4H2O6)2(H2O)8](ClO4)2·5H2O, 1, was synthesized in single crystal form by slowly evaporating an aqueous solution of potassium antimony tartrate and magnesium perchlorate. In the temperature interval 298 K–123 K, the compound undergoes two reversible structural phase transitions. The transition from phase I to phase II at ca. 236 K is second order and the transition from phase II to phase III at ca. 144 K is first order. Phase I has an orthorhombic structure, P21212, a=11.8658(4) Å, b=16.464(1) Å, c=8.3895(4) Å at 298 K, containing infinite chains of antimony tartrate dimeric clusters bridged by MgO2(H2O)4 octahedra. The ClO4 − anions occupying the interchain space show pronounced dynamic disorder. Phase II is monoclinic, P21, a=8.3813(8) Å, b=11.760(1) Å, c=16.289(2) Å, β=92.442(2)° at 153 K. Phase III has an orthorhombic unit cell with quadrupled cell volume, P212121, a=11.6914(8) Å, b=16.176(1) Å, c=33.426(2) Å at 123 K. While the infinite chains in phases II and III are closely similar to those in phase I, the ClO4 − anions show different orientations and gradual disappearance of dynamic disorder as the temperature is lowered.

Method and Basis Set Analysis of Oxorhenium(V) Complexes for Theoretical Calculations

A variety of method and basis set combinations has been evaluated for monooxorhenium(V) complexes with N, O, P, S, Cl, and Se donor atoms. The geometries and energies obtained are compared to both high-level computations and literature structures. These calculations show that the PBE0 method outperforms the B3LYP method with respect to both structure and energetics. The combination of 6-31G** basis set on the nonmetal atoms and LANL2TZ effective core potential on the rhenium center gives reliable equilibrium structures with minimal computational resources for both model and literature compounds. Single-point energy calculations at the PBE0/LANL2TZ,6-311+G* level of theory are recommended for energetics.