Understanding the Role of Aqueous Solution Speciation and Its Application to the Directed Syntheses of Complex Oxidic Zr Chlorides and Sulfates

Abstract

The lack of an in-depth understanding of solution-phase speciation and its relationship to solid-state phase formation is a grand challenge in synthesis science. It has severely limited the ability of inorganic chemists to predict or rationalize the formation of compounds from solutions. The need to investigate mechanisms that underlie self-assembly has motivated this study of aqueous Zr-sulfate chemistry as a model system, with the goal of understanding the structures of oligomeric clusters present in solution. We used high-energy X-ray scattering (HEXS) data to quantify Zr correlations in a series of solutions as a function of sulfate concentration. The pair distribution function (PDF) from the sulfate-free sample reveals that the average oligomeric Zr moiety is larger than the tetrameric building unit, [Zr4(OH)8(H2O)16](8+), generally understood to dominate its solution speciation. At sulfate concentrations greater than 1 m (molal), bidentate sulfate is observed, a coordination not seen in Zr(SO4)2·4H2O (2), which forms upon evaporation. Also seen in solution are correlations consistent with sulfate-bridged Zr dimers and the higher-order oligomers seen in 2. At intermediate sulfate concentrations there are correlations consistent with large Zr hydroxo-/oxo-bridged clusters. Crystals of [Zr18(OH)26O20(H2O)23.2(SO4)12.7]Cl0.6·nH2O (3) precipitate from these solutions. The Raman spectrum of 3 has a peak at 1017 cm(-1) that can be used as a signature for its presence in solution. Raman studies on deuterated solutions point to the important role of sulfate in the crystallization process. These solution results emphasize the presence of well-defined prenucleation correlations on length scales of <1 nm, often considered to be within the structurally amorphous regime.

In situ studies of a platform for metastable inorganic crystal growth and materials discovery

“…We observe a complex phase space: In all but one of our reactions we observe additional crystalline phases in situ that are not present by the end of the reaction (as would be recovered ex situ). Both families of ternary compounds can exhibit a variety of coordinations by sulfur, and the range of properties is accordingly large: In just one of our Cu-containing reactions we found a previously undiscovered 1D metal (K 3 Cu 4 S 4 ) similar to heavy-metal capture materials and observed a different 2D metal (K 3 Cu 8 S 6 ) and a layered semiconductor (KCu 3 S 2 ).Our approach can be combined with previous work that probes the formation and stabilization of inorganic materials from liquid media, using structural and spectroscopic data (19,20). Within a given reaction, we can use temperature as a variable to probe the relationships among phases with the goal of Significance Dense inorganic materials comprise most functional electronic, optical, and magnetic devices.…”

“…In KCu 3 S 2 these chains are linked by tetrahedral CuS 4 units to form a 2D network. The shared structural motifs suggest a common precursor may exist in the melt, and the implication for directing synthesis in regime can be probed by other in situ studies (19,20). Na 3 Cu 4 S 4 accommodates extra charge on Cu-S chains but curiously does not exhibit charge-density-wave modulations (31).…”

“…Our approach can be combined with previous work that probes the formation and stabilization of inorganic materials from liquid media, using structural and spectroscopic data (19,20). Within a given reaction, we can use temperature as a variable to probe the relationships among phases with the goal of Significance Dense inorganic materials comprise most functional electronic, optical, and magnetic devices.…”

Solvent extraction and separation of hafnium from zirconium using Ionquest 801

“…From a structural analysis point of view, Hu et al (2013) combined high-energy X-ray scattering (HEXS), Raman spectroscopy, and mathematical manipulations such as Fourier transformations and Gaussian curves to obtain partial pair distribution functions (PDFs). These PDFs show only those correlations involving Zr (specifically including those with complexed species, solvent molecules, and other solute ions) and represent electron counts in Zr ion correlations, enabling possible species to be characterized and elucidated according to relative intensities.…”

“…These PDFs show only those correlations involving Zr (specifically including those with complexed species, solvent molecules, and other solute ions) and represent electron counts in Zr ion correlations, enabling possible species to be characterized and elucidated according to relative intensities. Hu et al (2013, Figure 4) plotted changes in the integrated intensities of selected PDF peaks (3.56, 4.97, and 6.7 Å) as a function of the total sulphate concentration in solution. All three peaks increase in intensity up to [SO 4 2-] = 0.5 M with the peaks at 4.97 and 6.7…”