Predicting the Solubility of Inorganic Ion Pairs in Water.

Polyoxometalates (POMs), ranging in size from 1 to 10's of nanometers, resemble building blocks of inorganic materials. Elucidating their complex solubility behavior with alkali-counterions can inform natural and synthetic aqueous processes. In the study of POMs ([Nb O H ] , Nb ) we discovered an unusual solubility trend (termed anomalous solubility) of alkali-POMs, in which Nb is most soluble with the smallest (Li ) and largest (Rb/Cs ) alkalis, and least soluble with Na/K .

NbO, LiNbO, and (Na, K)NbO Thin Films from High-Concentration Aqueous Nb-Polyoxometalates.

Synthesizing functional materials from water contributes to a sustainable energy future. On the atomic level, water drives complex metal hydrolysis/condensation/speciation, acid-base, ion pairing, and solvation reactions that ultimately direct material assembly pathways. Here, we demonstrate the importance of Nb-polyoxometalate (Nb-POM) speciation in enabling deposition of NbO, LiNbO, and (Na, K)NbO (KNN) from high-concentration solutions, up to 2.

Oxo-Cluster-Based Zr/Hf Separation: Shedding Light on a 70-Year-Old Process.

Zirconium and hafnium in the tetravalent oxidation state are considered the two most similar elements on the periodic table, based on their coexistence in nature and their identical solid-state chemistry. However, differentiating solution phase chemistry is crucial for their separation for nuclear applications that exploit the neutron capture of Hf and neutron transparency of Zr. Here we provide molecular level detail of the multiple factors that influence Zr/Hf separation in a long-exploited, empirically designed industrial solvent-extraction process that favors Hf extraction into an organic phase.

Solvent-Driven Transformation of Zn/Cd-Deoxycholate Assemblies.

Deoxycholic acid (DOC) is a unique, biologically derived surfactant with facial amphiphilicity that has been exploited, albeit minimally, in supramolecular assembly of materials. Here, we present the synthesis and structural characterization of three hybrid metal (Zn and Cd)-DOC compounds. Analysis by single-crystal X-ray diffraction reveals the many interactions that are possible between these facial surfactants and the influence of solvent molecules that drive the assembly of materials.

Deliberate Construction of Polyoxoniobates Exploiting the Carbonate Ligand.

Polyoxometalates (POMs, metals=V , Nb , Ta , Mo , W ) are molecular metal oxides that can be isolated without capping ligands. The high negative charge of polyoxoniobates (PONb) provides strong interactions with heterocations, advantageous for electrostatic assembly of modular materials. In four single-crystal X-ray structures, we demonstrate that carbonate combined with the very reactive decaniobate [Nb O ] reassembles into a new decaniobate, [Nb O (CO ) ] , featuring three carbonate-ligated Nb-polyhedra.

Differentiating Zr/Hf Aqueous Polyoxocation Chemistry with Peroxide Ligation.

This work complements our recent discovery of new phases derived from zirconium perchlorate by addition of hydrogen peroxide. Here, we investigate analogous reactions with hafnium perchlorate, which is found to have modifications of the Clearfield-Vaughan tetramer (CVT). For hafnium perchlorate derivatives, we find distorted versions of CVT by X-ray diffraction and study the reaction solutions by SAXS, Raman spectroscopy, and ESI-MS.

Directional Bonding in Decaniobate Inorganic Frameworks.

Metal-oxo clusters offer an opportunity to assemble inorganic and metal-organic frameworks (MOFs) by a controlled building-block approach, which led to the revolutionary discoveries of zeolites and MOFs. Polyoxometalate clusters are soluble in water, but more challenging to link into frameworks; the inert oxo-caps that provide solubility are resistant to replacement or further connectivity. We demonstrate how the unique directional bonding and varying basicity of the decaniobate ([Nb ]) oxo-caps can be exploited to build 1D, 2D, and 3D inorganic frameworks.

Bismuth for Controlled Assembly/Disassembly of Transition-Metal Oxo Clusters, Defining Reaction Pathways in Inorganic Synthesis and Nature.

Trivalent bismuth is a unique heavy p-block ion. It is highly insoluble in water, due to strong hydrolysis tendencies, and known for low toxicity. Its lone pair is structure-directing, providing framework materials with structural flexibility, leading to piezoelectric and multiferroic function.

The Role of the Organic Solvent Polarity in Isolating Uranyl Peroxide Capsule Fragments.

Uranyl peroxide capsules are a fascinating class of polyoxometalates (POMs), discovered only in the 21st century. Understanding the reactivity between peroxide, alkali cations, and uranyl in alkaline solutions is important in nuclear science disciplines including mineralogy, nuclear energy, and legacy nuclear wastes. Here, we have developed a general procedure to isolate different fragments of the uranyl-peroxide POM capsules, using organic solvents to partially remove K salts from crude solids of the monomer building block UO(O) (), leading to stabilization of these reactive fragments.

Peroxide-Promoted Disassembly Reassembly of Zr-Polyoxocations.

Zr/Hf aqueous-acid clusters are relevant to inorganic nanolithography, metal-organic frameworks (MOFs), catalysis, and nuclear fuel reprocessing, but only two topologies have been identified. The () polyoxocation is the ubiquitous square aqueous Zr/Hf-oxysalt of all halides (except fluoride), and prior-debated for perchlorate. Simply adding peroxide to a Zr oxyperchlorate solution leads to a striking modification of , yielding two structures identified by single-crystal X-ray diffraction.

Time-controlled synthesis of the 3D coordination polymer U(1,2,3-Hbtc) followed by the formation of molecular poly-oxo cluster {U} containing hemimellitate uranium(iv).

Two coordination compounds bearing tetravalent uranium were synthesized in the presence of tritopic hemimellitic acid in acetonitrile with a controlled amount of water (HO/U ≈ 8) and structurally characterized. Compound 1, [U(1,2,3-Hbtc)]·0.5CHCN is constructed around an eight-fold coordinated uranium cationic unit [UO] linked by the poly-carboxylate ligands to form dimeric subunits, which are further connected to form infinite corrugated ribbons and a three-dimensional framework.

The role of titanium-oxo clusters in the sulfate process for TiO production.

TiO is manufactured for white pigments, solar cells, self-cleaning surfaces and devices, and other photocatalytic applications. The industrial synthesis of TiO entails: (1) the dissolution of ilmenite ore (FeTiO) in aqueous sulfuric acid which precipitates the Fe while retaining the Ti in solution, followed by (2) dilution or heating the Ti sulfate solution to precipitate the pure form of TiO. The underlying chemistry of these processing steps remains poorly understood.

Strategic Capture of the {Nb } Polyoxometalate.

Group V Nb-polyoxometalate (Nb-POM) chemistry generally lacks the elegant pH-controlled speciation exhibited by group VI (Mo, W) POM chemistry. Here three Nb-POM clusters were isolated and structurally characterized; [Nb O (O ) H ] , [((UO )(H O)) Nb (UO ) O H (H O) ] , and [(Nb O H ) (UO ) (H O) ] , that effectively capture the aqueous Nb-POM species from pH 7 to pH 10. These Nb-POMs illustrate a reaction pathway for control over speciation that is driven by counter-cations (Li ) rather than pH.

Energetic Trends in Monomer Building Blocks for Uranyl Peroxide Clusters.

The uranyl triperoxide anionic monomer is a fundamental building block for uranyl peroxide polyoxometalate capsules. The reaction pathway from the monomer to the capsule can be greatly altered by the counterion: both the reaction rate and the resulting capsule structure. We synthesized and characterized uranyl triperoxides MgUO(O)·13HO (MgUT), CaUO(O)·9HO (CaUT), SrUO(O)·9HO (SrUT), and KUO(O)·3HO (KUT) and compared their thermodynamic stabilities.

{Np} clusters: the missing link in the largest poly-oxo cluster series of tetravalent actinides.

Two poly-oxo cluster complexes of tetravalent neptunium (Np(iv)), Np38O56Cl18(bz)24(THF)8·nTHF and Np38O56Cl42(ipa)20·mipa (bz = benzoate, THF = tetrahydrofuran, and ipa = isopropanol), were obtained via solvothermal synthesis and structurally characterised by single-crystal X-ray diffraction. The {Np38} clusters are comparable to the analogous {U38} and {Pu38} motifs, filling the gap in this largest poly-oxo cluster series of tetravalent actinides.

Formation of a new type of uranium(iv) poly-oxo cluster {U} based on a controlled release of water esterification reaction.

A new strategy for the synthesis of large poly-oxo clusters bearing 38 tetravalent uranium atoms {U} has been developed by controlling the water release from the esterification reaction between a carboxylic acid and an alcohol. The molecular entity [UOCl(HO)(ipa)]·(ipa) (ipa = isopropanol) was crystallized from the solvothermal reaction of a mixture of UCl and benzoic acid in isopropanol at temperature ranging from 70 to 130 °C. Its crystal structure reveals the molecular assembly of the UO fluorite-like inner core {U} with oxo groups bridging the uranium centers.

Synthesis of Coordination Polymers of Tetravalent Actinides (Uranium and Neptunium) with a Phthalate or Mellitate Ligand in an Aqueous Medium.

Four metal-organic coordination polymers bearing uranium or neptunium have been hydrothermally synthesized from a tetravalent actinide chloride (AnCl) and phthalic (1,2-Hbdc) or mellitic (Hmel) acid in aqueous media at 130 °C. With the phthalate ligand, two analogous assemblies ([AnO(HO)(1,2-bdc)]·HO; An = U (1) or Np (2)) have been isolated, in which the square-antiprismatic polyhedra of AnO are linked to each other via μ-oxo groups with an edge-sharing mode to materialize infinite zigzag ribbons. The phthalate molecules play a role in connecting the adjacent zigzag chains to build a two-dimensional (2D) network.

Hydrothermal Crystallization of Uranyl Coordination Polymers Involving an Imidazolium Dicarboxylate Ligand: Effect of pH on the Nuclearity of Uranyl-Centered Subunits.

Four uranyl-bearing coordination polymers (1-4) have been hydrothermally synthesized in the presence of the zwitterionic 1,3-bis(carboxymethyl)imidazolium (= imdc) anion as organic linkers after reaction at 150 °C. At low pH (0.8-3.