[Pb2F2](SeO4): a heavier analogue of grandreefite, the first layered fluoride selenate

Abstract

This relatively low-temperature process involves complete rearrangement of the crystal structure-from a 2D architecture featuring slabs [Pb 2 F 2 ] 2+ formed by fluorine-centered tetrahedra into a structure characterized by 1D motifs based on [OPb 2 ] 2+ chains of oxocentered tetrahedra. The comparative crystal chemistry of the obtained anion-centered structural architectures is discussed. (Siidra et al. 2013c(Siidra et al. , 2015. Most of these structures can be notionally decomposed into tetragonal subcells with an a parameter similar to that of litharge (commonly 3.75-4.35 Å, depending on the layer composition), while c can vary over a wide range (from 5 to more than 75 Å) as might be expected for layered structures (Charkin 2008). Within these "archetypic" subcells, the 2 ∞ [XM] (X = anion, M = cation) slabs contain two X and two M atoms; they are positively charged and interleave with various anionic species. The OM 4 oxocentered tetrahedra, with M = Pb 2+ , Bi 3+ or rare-earth elements, are the most common contributors to these slabs. Second rank the FM 4 fluoride-centered tetrahedra with M being rare-earth or alkaline-earth elements, but most commonly Pb 2+ . [Pb 2 F 2 ] 2+ slabs have been found in the structures of the minerals matlockite [Pb 2 F 2 ](Cl) 2 (c = 9 Å) (Pasero and Perchiazzi 1996), grandreefite [Pb 2 F 2 ](SO 4 ) (c = 14 Å)

Expanding Family of Litharge-Derived Sulfate Minerals and Synthetic Compounds: Preparation and Crystal Structures of [Bi2CuO3]SO4 and [Ln2O2]SO4 (Ln = Dy and Ho)

“…Synthetic analogs of [Ba 2 F 2 ]S 2 O 3 were found among [Ln 2 O 2 ]CrO 4 oxychromates (Ln = Pr-Tb [33]). Synthetic analogs of the grandreefite structure are observed also among selenates ([Pb 2 F 2 ]SeO 4 [34] and [Ln 2 O 2 ]SeO 4 , Ln = La, Pr, Nd [35]) and chromates ([La 2 O 2 ]CrO 4 [32]). The same structure was also established for [Bi 2 O 2 ]SO 4 [36] and some rare-earth oxysulfates [Ln 2 O 2 ]SO 4 (La [29], Sm [30] and Eu [31]).…”

“…Structurally related architectures occur when the interlayer gallery hosts various molecular anions (linear triatomic [20,21], trigonal [22][23][24][25][26], or tetrahedral [27][28][29][30][31][32][33][34][35][36][37][38] (Figure 1a-h). There are three possible orientations of tetrahedral anions between the litharge slabs (Figure 1d-f) two of which are represented in nature by the mineral grandreefite [Pb 2 F 2 ]SO 4 [27] and a slag phase [Ba 2 F 2 ]S 2 O 3 [28].…”

Structural, thermal, and IR studies of β-[Nd2O2](CrO4), an unexpected analog of a slag phase [Ba2F2](S6+O3S2−)

“…Several attempts to resolve the disorder in the doubled unit cells as reported in [4,11] remained unsuccessful. The methods and software utilized were the same [21] as used previously for the structure determination of related layered lead compounds [12,23].…”

“…Fluoride analogs of the oxide compounds were also reported, viz. [Pb 2 F 2 ](MO 4 ) (M = S, Se [11,12]) and, notably, a unique thiosulfate bearing slag phase of composition [Ba 2 F 2 ] (S 6+ O 3 S 2− ) [13].…”

“…[17], but the crystal structures could not be determined despite numerous attempts. Our recent investigations have shown that the structure determination of such compounds may be severely hampered by the observation that several sets of unit cell parameters may yield fairly similar indexing FOMs [12]. Therefore, the unit cell used initially for the structural determination of Nd 2 CrO 6 might be not the right one.…”