Polyoxometalate chemistry at volcanoes: discovery of a novel class of polyoxocuprate nanoclusters in fumarolic minerals

Abstract

Polyoxometalate (POM) chemistry is an important avenue of comprehensive chemical research, due to the broad chemical, topological and structural variations of multinuclear polyoxoanions that result in advanced functionality of their derivatives. the majority of compounds in the polyoxometalate kingdom are synthesized under laboratory conditions. However, Nature has its own labs with the conditions often unconceivable to the mankind. The striking example of such a unique environment is volcanic fumaroles-the natural factories of gas-transport synthesis. We herein report on the discovery of a novel class of complex polyoxocuprates grown in the hot active fumaroles of the Tolbachik volcano at the Kamchatka Peninsula, Russia. The cuboctahedral nanoclusters {[Mcu 12 o 8 ](AsO 4) 8 } are stabilized by the core Fe(III) or Ti(IV) cations residing in the unique cubic coordination. The nanoclusters are uniformly dispersed over the anion-and cation-deficient NaCl matrix. Our discovery might have promising implications for synthetic chemistry, indicating the possibility of preparation of complex polyoxocuprates by chemical vapor transport (CVT) techniques that emulate formation of minerals in high-temperature volcanic fumaroles. Polyoxometalates (POMs) constitute a large group of materials with discrete metal-anion clusters of various shapes and sizes 1-3. Traditionally, POMs were associated with d-block metals in high oxidation states (V 5+ , Nb 5+ , Ta 5+ , Mo 6+ and W 6+), but recent studies extended the field to other elements such as actinides 4 and noble metals 5. In 1990, Achim Müller and co-workers 6 introduced the term 'polyoxocuprates' (POCus) to identify clusters formed by polymerization of Cu coordination polyhedra, previously reported for synthetic inorganic compounds such as Ba 44 Cu 45 O 87 Cl 4 and Ba 88 Cu 88 O 175 Br 2

Structural and chemical complexity of minerals: an update

“…The list of twenty most structurally complex minerals known so far given in Table 3 reveals the following most important complexity-generating mechanisms in minerals: the presence of large (sometimes nanometre-scale) clusters such as polyoxometalates or related finite-cluster structures (Krivovichev, 2020b) isolated from each other; such multinuclear atomic units possess a large number of atoms with different topological functions; the examples are ewingite, morrisonite, vanarsite, bouazzerite and postite; as a rule, natural polyoxometalate minerals are also highly hydrated, with the exception of arsmirandite and lehmannite, which are anhydrous polyoxocuprates formed in volcanic fumaroles (Britvin et al , 2020); the presence of large clusters linked together to form three-dimensional frameworks; the examples are ilmajokite and paddlewheelite (both minerals are also highly hydrated, which contributes greatly to their structural complexities); the formation of complex three-dimensional modular frameworks formed by cages of different sizes and topologies; this complexity type corresponds to paulingite-group minerals, fantappièite and sacrofanite (members of the sodalite–cancrinite ABC series (Bonaccorsi and Nazzareni, 2015; Chukanov et al , 2021), tschörtnerite, mendeleevite-(Ce) and rowleyite; the formation of complex layers with different combinations of modules (chains or rings); this type is characteristic for layered uranyl minerals (such as vandendriesscheite and gauthierite) and layered silicates (parsettensite); a high hydration state in salts with complex heteropolyhedral units (alfredstelznerite and voltaite-group minerals); the formation of ordered superstructures of relatively simple structure types; the examples are meerschautite (which is the only sulfide species in the list and was described by Biagioni et al (2016) as an expanded derivative of owyheeite) and manitobaite (that has a fivefold superstructure relative to alluaudite (Tait et al , 2011)); for further discussion on the relations between superstructures and complexity see Krivovichev et al (2019a, 2021), Kornyakov et al (2021) and Kornyakov and Krivovichev (2021). …”

“…the presence of large (sometimes nanometre-scale) clusters such as polyoxometalates or related finite-cluster structures (Krivovichev, 2020b) isolated from each other; such multinuclear atomic units possess a large number of atoms with different topological functions; the examples are ewingite, morrisonite, vanarsite, bouazzerite and postite; as a rule, natural polyoxometalate minerals are also highly hydrated, with the exception of arsmirandite and lehmannite, which are anhydrous polyoxocuprates formed in volcanic fumaroles (Britvin et al , 2020);…”

Polyoxometalate clusters in minerals: review and complexity analysis

“…Most of the POM clusters in minerals are usually associated with crystallization from aqueous solutions. Britvin et al (2020) reported recently on the discovery of two fumarolic minerals, arsmirandite and lehmannite, which formed directly from volcanic gases. The basic structural unit in both structures is a novel nanoscale ($1.5 nm across) polyoxocuprate cluster with the composition {[MCu 12 O 8 ](AsO 4 ) 8 } (M = Fe 3+ and Ti 4+ , for arsmirandite and lehmannite, respectively; Fig.…”

“…in natrophosphate). The special case is exemplified by the polyoxocuprate clusters in arsmirandite and lehmannite, where they are immersed into a deficient NaCl matrix that stabilizes the cluster surface via ionic interactions (Britvin et al, 2020). Similarly to synthetic compounds, in the crystal structures of natural POMs, the clusters are held together via hydrogen bonds and ionic bonds to alkaline or alkaline earth cations that are much weaker than the Me-O bonds inside the clusters.…”

A Novel Mineral-like Copper Phosphate Chloride with a Disordered Guest Structure: Crystal Chemistry and Magnetic Properties

“…Among them, polyoxocuprates (POCus) have been distinguished, showing cross-structural topological transformations related to their multiple physical properties in homogeneous photocatalysis, medical chemistry, molecular magnetism, and quantum computing [8]. Recent discoveries of new rare and complex minerals demonstrate the presence of natural POMs and POCus in geochemical systems [9,10]. Here, we report the hydrothermal synthesis, crystal structure, and physical properties of new complex copper phosphate chloride, Na 2 Li 0.75 (Cs,K) 0.5 [Cu 5 (PO 4 ) 4 Cl]•3.5(H 2 O,OH), which is a new member of the polysomatic series of the lavendulan mineral group.…”