Anastasiya I. Zadoya

Synthesis and Modular Structural Architectures of Mineralogically Inspired Novel Complex Pb Oxyhalides

Three novel Pb oxyhalides, Pb3[O10Pb20](GeO4)4Cl10 (1), [O16Pb22][OPb](OH)I10(I,Br)(H2O) (2), and Pb5.5Si0.5O6Cl (3), have been prepared by high-temperature solid-state reactions (1 and 3) and hydrothermal method (2). The structure of 1 is based upon novel [O10Pb20](20+) layers of edge- and corner-sharing oxocentered OPb4 tetrahedra with cavities occupied by the GeO4 tetrahedral anions. The interlayer space contains low-occupied Pb sites and Cl(-) anions. The structure of 2 contains unique [O16Pb22][12+] layers of edge-sharing OPb4 tetrahedra with X(-) ions (X = I, Br) in and in between the layers. The structure of 3 is the first example of the Pb oxyhalide with the 3:1 ratio between the O-Pb and X sheets (X = halide). The unprecedented structure topologies and architectures observed in the title compounds are closely related to those observed in rare natural Pb oxyhalides that have no synthetic analogues to date.

Formation of co-racemic uranyl chromate constructed from chiral layers of different topology

Four new inorganic uranyl chromates were obtained by evaporation and hydrothermal methods: [(CH3)2NH2]2[(UO2)2(CrO4)3(H2O)](H2O) (1), K(Rb0.6K0.4)[(UO2)2(CrO4)3(H2O)](H2O)3 (2) [(CH3)3CNH3]2[(UO2)2(CrO4)3H2O] (3), [(CH3)2NH2]4[(UO2)2(CrO4)3H2O]2(H2O) (4). Their structures are based on two-dimensional chiral or achiral units with the composition [(UO2)2(CrO4)3(H2O)]2− and two types of topologies (A or/and B). The structural architecture of (4) is unique amongst all known uranyl-based structures, and unusual among hybrid organic/inorganic structures in general as it contains layers of identical composition, but of different topology. The unique structural configurations and non-centrosymmetry in (1) and (4) is governed by selective formation of hydrogen bonding rather than by the formation of hydrophobic and hydrophilic zones in the organic interlayer. It is shown that chiral architectures in uranyl systems may form from achiral building units as observed in (3) and (4). This is somewhat analogous to certain organic compounds, where achiral molecules are also able to form chiral layers. Within the concept of such an interpretation the structure of (3) can then be described as a racemate consisting of two A and A′ chiral layers. In a similar approach the structure of (4) can be interpreted as being formed by four chiral layers. Layer pairs AA′ and BB′ can then be considered as racemic pairs and the whole structure is a co-racemate built by a combination of two racemates. Two-stage formation can be suggested for (4).

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

Abstract A family of Ln2CrO6 (Ln=Pr, Nd, Sm–Tb) compounds has been re-investigated using powder X-ray diffraction and IR spectroscopy. The structure of β-Nd2CrO6≡β-[Nd2O2](CrO4) is similar to that of the slag compound [Ba2F2](S6+O3S2−) in that it exhibits a disordered arrangement of (CrO4)2− anions between [Nd2O2]2+ litharge-type blocks. Its structural architecture is also related to other layered α- and γ-[Ln2O2](AO4) species (A=S, Cr, Mo), showing various orientations of the tetrahedral anions within the interlayer space. Size relationships between the incorporated tetrahedral anions and formation of different structure types (denoted as M1-, M2- and T-type) are reviewed. The possible existence of new compounds which are isostructural with, or structurally related to, β-[Nd2O2](CrO4) and bearing other transition metal-centred tetrahedral anions are discussed.

Structural variations of uranium compounds with nitrate anions

The nitrate anion, NO 3 – , is known to be widely used in different stages of the PUREX (Plutonium and Uranium Recovery by Extraction) process [1]. By changing nitrate concentration of the initial solution, one may control separation of actinides by various procedures. Three major coordination environments by ligands are observed for linear (UO 2 ) 2+ uranyl (Ur) ion in oxocompounds. It is typically coordinated by four, five or six ligands, arranged at the equatorial vertices of UrO 4 (square), UrO 5 (pentagonal bipyramid) or UrO 6 (hexagonal bipyramid), respectively. Nitrate groups in inorganic uranium compounds may either directly coordinate uranyl ion thus forming [(UO 2 )(NO 3 ) n X m ] or being bonded to interstitial cations only with formation of [(UO 2 )X m ](NO 3 ) n complexes, where X = O, Cl, Br. Four new uranyl-nitrate compounds were obtained from aqueous solutions: (CH 3 ) 2 (NH 2 ) 2 [(UO 2 ) 2 (NO 3 ) 2 (CrO 4 ) 2 (H 2 O)]H 2 O (1), (15-crown5) 2 [(UO 2 ) 2 (H 2 O) 4 (O 2 )(NO 3 ) 2 ](H 2 O) 3.5 (2) , Cs 2 [(UO) 2 (NO 3 ) 4 (OH) 2 ] (3) and Rb 3 [(UO 2 )Cl 3 (NO 3 )](NO 3 ) (4). The structure of 1 is the first observation of one-dimensional unit (chain) with nitrate groups coordinating UrO 6 hexagonal pyramids and formation of [(UO2)2(NO3)2(CrO4)2(H2O)]. Compound 2 is a rare example of organically templated uranyl compound containing peroxide component with neutral organic and inorganic constituents. Neutral 15-crown5 and H2O molecules are packed around [(UO2)2(H2O)4(O2)(NO3)2] units providing structural stability exclusively via hydrogen and Van-derWaals bonding. [(UO) 2 (NO 3 ) 4 (OH) 2 ] clusters in the structure of 3 were not previously observed in inorganic compounds without organic molecules. And the structure of 4 contains both, NO3directly coordinating uranyl and nitrate bonded to Rb atoms only. The latter is reflected in the structural formula of 4. This work was supported by the Saint-Petersburg State University internal grant 3.38.238.2015.

Crystal chemistry of layered Pb oxyhalides: crystal structure of Pb3[Pb20O10](GeO4)Cl10

Pb oxyhalides are of interest due to their environmental and technological importance. They are also known as important constituents of oxidation zones of mineral deposits. Most Pb oxyhalides have layered α-PbO-derivative structures, which are related to the Aurivillius phases. The crystal structures of Pb-O related layered lead oxyhalides are based upon the O−Pb layers alternating with the X sheets of X− ions (X = Cl, Br, I). The PbO-derivative compounds may also incorporate a wide range of elements, including As, S, V, Mo, W, P, Si, etc., which results in interesting chemical and structural diversity and complexity. Pb3[Pb20O10](GeO4)Cl10 (1) was obtained by rapid quenching of lead-oxyhalide melt [1]. The structure of 1 (Cmca, a = 28.352(19), b = 11.116(7), c = 16.513(11) Å, V = 5204(6) Å3, R1 = 0.0504) contains 7 symmetrically independent Pb sites. Pb(6) site is splitted into less occupied Pb6A and Pb6B sites. The coordination environments of the Pb atoms are variable in agreement with the presence of stereochemically active “lone pairs” on divalent lead cations. The structure of 1 contains one Ge site coordinated tetrahedrally by four O atoms with the average bond length equal to 1.75 Å. The total number of oxygen sites is seven. The O(3), O(4), O(6), and O(7) sites are bonded to Ge, whereas other O atoms (O(1), O(2), O(5)) are tetrahedrally coordinated by Pb atoms, which results in formation of oxocentered OPb4 tetrahedra. 1 belongs to the 1:1 type and consists of alternating PbO-type layers and mixed Pb−Cl sheets oriented parallel to (100). The PbO-type layer is a derivative of the [OPb] tetrahedral layer in α-PbO and can be obtained from the latter by removal of blocks of oxocentered tetrahedra. The GeO4 tetrahedral anions locate in the cavities within the PbO-type layer. The formula of the layer can be written as [O10Pb20]20+. The structure of 1 illustrates the complexity of the lead oxyhalide systems and validates new pathways for synthesis of complex Pb oxyhalides.