Na_nMTh₆F₃₀: A Large Family of Quaternary Thorium Fluorides

Abstract

Recently we reported the synthesis, crystal structures, and magnetic properties of compounds in the Na n MU 6 F 30 series, where n = 4, 3 and where M is a divalent or trivalent metal cation, respectively. In this article we advance our investigation of this structure type by expanding it to the thorium-containing compounds Na n MTh 6 F 30 , where n = 3 in the case of M III = Al, Sc, Ti, V, Cr, Fe, Ga, In, n = 4 when M II = Mg, Mn, Co, Ni, Cu, Zn, and n varies from 3.87 to 4.39 when the M site is partially occupied by a trivalent rareearth element. Magnetic properties of the compounds containing magnetic ions M = Ti 3+ , V 3+ , Cr 3+ , Mn 2+ , Fe 3+ , Co 2+ , Ni 2+ , Cu 2+ were studied to demonstrate that the substitution of Th(IV) for U(IV) prevents the magnetic ions from coupling magnetically and, therefore, they exhibit simple paramagnetic behavior.

Expansion of the Na3MIII(Ln/An)6F30 Series: Incorporation of Plutonium into a Highly Robust and Stable Framework

“…The composition and the oxidation states (by charge balance and bond distances) of the elements in Na 3 MPu 6 F 30 (M=Al 3+ , Fe 3+ , Co 3+ ) and Na 2.4 Mn 1.6 Pu 6 F 30 compounds were determined using single crystal X‐ray diffraction. All compounds crystallize in the trigonal space group P c 1 and are isostructural to the Ce, Th, and U phases described in detail previously . All atoms in the structures of Na 3 MPu 6 F 30 (M=Al 3+ , Fe 3+ , Co 3+ ) are fully occupied and ordered.…”

“…We have extensively studied the Na n M(Ln/An) 6 F 30 series and have previously identified phase boundaries for the formation of Na 4 M II (Ln/An) 6 F 30 versus Na 3 M III (Ln/An) 6 F 30 on the basis of M 2+ /M 3+ and Ln 4+ /An 4+ sizes . It was determined that compositions containing the larger Th 4+ and U 4+ cations can accommodate a variety of di‐ and trivalent metal cations ranging in size from Al 3+ (Shannon radius of six‐coordinated Al 3+ , 0.675 Å) to Mn 2+ (0.97 Å), while compositions containing the smaller Ce 4+ cation are limited to the incorporation of only the smaller trivalent metal cations (Al 3+ , 0.675 Å; Ga 3+ , 0.760 Å; Fe 3+ , 0.785 Å; Cr 3+ , 0.755 Å).…”

“…We have extensively studied the Na n M(Ln/An) 6 F 30 series and have previously identified phaseb oundaries for the formation of Na 4 M II (Ln/An) 6 F 30 versus Na 3 M III (Ln/An) 6 F 30 on the basis of M 2 + /M 3 + and Ln 4 + /An 4 + sizes. [17][18][19][20] It was determined that compositions containing the larger Th 4 + and U 4 + cations can accommodate av arietyo fd i-and trivalent metal cationsr anging in size from Al 3 + (Shannon radius of six-coordinated Al 3 + , 0.675 )t oM n 2 + (0.97 ), [21] while compositions containing the smaller Ce 4 + cation are limited to the incorporation of only the smaller trivalent metal cations (Al 3 + ,0 .675 ;G a 3 + ,0 .760 ; Fe 3 + ,0 .785 ;C r 3 + ,0 .755 ). Given the similarityi ns ize between Ce 4 + and Pu 4 + we expectedt he plutoniums eries to exhibit at rend similart ot he one found for Ce 4 + ;h owever,d ifferences in their redox behavior,afactor which hadn ot seemed to play as ignificant role in the formation of the other members of the Na n M(Ln/An) 6 F 30 series, gave rise to notable differences between the cerium and plutonium systems.…”

“…All compounds crystallize in the trigonal space group P3 ¯c1a nd are isostructural to the Ce, Th, and Up hases described in detail previously. [17][18][19][20] All atoms in the structures of Na 3 MPu 6 F 30 (M = Al 3 + , Fe 3 + ,C o 3 + )a re fully occupied and ordered. As shown in Figure 2, the three-dimensional Pu 6 F 30 6À framework is made up of PuF 9 polyhedra connected to form channels containing charge-balancing M n + (Wyckoff site 2a)a nd Na + cations (site 4d); as econd set of crystallographically unique Na + cations (site 2b)a lso reside in the larger voids between MF 6 octahedra.…”

“…Considering the likelihood of in situ reduction of strongly oxidizing Co 3 + and, to al esser degree, Mn 3 + ,t he originalr eports on the Na 3 MCe 6 F 30 and Na n MTh 6 F 30 series did not discusst he outcomes of reaction attempts using Mn 3 + or Co 3 + . [17,18] To better understand the processes taking place during the reactions, we subsequently attempted to investigate both the cerium and thorium systems with respectt oC o 3 + /Co 2 + and Mn 3 + / Mn 2 + redoxc hemistry,t he results of which are summarized in Ta ble 1. In reactions startingw ith Co 3 + ,o nly Co 2 + containing phases were obtainedw hereas in the reactions beginning with Mn 3 + ,t he novel phases Na 2.6 Mn II/III 1.4 Ce 6 F 30 and Na 3 Mn III Th 6 F 30 crystallized (Table S3).…”