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. Furthermore, we investigate mixed Hf–Zr solution and solid phases and find the latter resemble the zirconium family at low Hf concentrations and the hafnium family at higher hafnium contents.

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. In the aqueous solution, both Hf and Zr form an oxo-centered tetramer cluster with a core formula of [OM4(OH)6(NCS)12]4– (OM 4 -NCS, M = Hf, Zr). This was identified by single-crystal X-ray diffraction, as well as small-angle X-ray scattering (SAXS), of both the aqueous and organic phase. In addition to this phase, Zr also forms (1) a large oxo-cluster formulated [Zr48O30(OH)92(NCS)40(H2O)40] (Zr 48 ) and (2) NCS adducts of OZr 4 -NCS. Zr 48 was identified first by SAXS and then crystallized by exploiting favorable soft-metal bonding to the sulfur of NCS. While the large Zr 48 likely cannot be extracted due to its larger size, the NCS adducts of OZr 4 -NCS are also less favorable to extraction due to the extra negative charge, which necessitates coextraction of an additional countercation (NH4 +) per extra NCS ligand. Differentiating Zr and Hf coordination and hydrolysis chemistry adds to our growing understanding that these two elements, beyond simple solid-state chemistry, have notable differences in chemical reactivity.

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 24 O 72 H 9 ] 15À , Nb 24 ) we discovered an unusual solubility trend (termed anomalous solubility) of alkali-POMs, in which Nb 24 is most soluble with the smallest (Li + ) and largest (Rb/Cs + ) alkalis, and least soluble with Na/K + . Via computation, we define a descriptor (σprofile) and use an artificial neural network (ANN) to predict all three described alkali-anion solubility trends: amphoteric, normal

Directed synthesis promises control over architecture and function of framework materials. In practice, however, designing such syntheses requires a detailed understanding of the multistep pathways of framework formations, which remain elusive. By identifying intermediate coordination complexes, this study provides insights into the complex role of a structure-directing agent (SDA) in the synthetic realization of a promising material. Specifically, a novel molecular intermediate was observed in the formation of an indium zeolitic metal–organic framework (ZMOF) with a sodalite topology. The role of the imidazole SDA was revealed by time-resolved in situ powder X-ray diffraction (XRD) and small-angle X-ray scattering (SAXS).

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 ([Nb24O72H9]15−, Nb24) we discovered an unusual solubility trend (termed anomalous solubility) of alkali‐POMs, in which Nb24 is most soluble with the smallest (Li+) and largest (Rb/Cs+) alkalis, and least soluble with Na/K+. Via computation, we define a descriptor (σ‐profile) and use an artificial neural network (ANN) to predict all three described alkali‐anion solubility trends: amphoteric, normal (Li+>Na+>K+>Rb+>Cs+), and anomalous (Cs+>Rb+>K+>Na+>Li+). Testing predicted amphoteric solubility affirmed the accuracy of the descriptor, provided solution‐phase snapshots of alkali–POM interactions, yielded a new POM formulated [Ti6Nb14O54]14−, and provides guidelines to exploit alkali–POM interactions for new POMs discovery.