Andrey A. Zolotarev

Crystal chemistry of natural layered double hydroxides. I. Quintinite-2H-3c from the Kovdor alkaline massif, Kola peninsula, Russia

Abstract The crystal structure of quintinite-2H-3c, [Mg4Al2(OH)12](CO3)(H2O)3, from the Kovdor alkaline massif, Kola peninsula, Russia, was solved by direct methods and refined to an agreement index (R1) of 0.055 for 484 unique reflections with |Fo| ≥ 4σF. The mineral is rhombohedral, R32, a = 5.2745(7), c = 45.36(1) Å. The diffraction pattern of the crystal has strong and sharp Bragg reflections having h-k = 3n and l = 3n and lines of weak superstructure reflections extended parallel to c* and centred at h-k ≠ 3n. The structure contains six layers within the unit cell with the layer stacking sequence of ...AC=CA=AC=CA=AC=CA... The Mg and Al atoms are ordered in metal hydroxide layers to form a honeycomb superstructure. The full superstructure is formed by the combination of two-layer stacking sequence and Mg-Al ordering. This is the first time that a long-range superstructure in carbonate-bearing layered double hydroxide (LDH) has been observed. Taking into account Mg-Al ordering, the unique layer sequence can be written as ...=Ab1C=Cb1A=Ab2C=Cb2A=Ab3C=Cb3A=... The use of an additional suffix is proposed in order to distinguish between LDH polytypes having the same general stacking sequence but with different c parameters compared with the ‘standard’ polytype. According to this notation, the quintinite studied here can be described as quintinite-2H-3c or quintinite-2H-3c[6R], indicating the real symmetry.

Crystal chemistry of natural layered double hydroxides. 2. Quintinite-1M: first evidence of a monoclinic polytype in M2+-M3+ layered double hydroxides

Abstract Quintinite-1M, [Mg4Al2(OH)12](CO3)(H2O)3, is the first monoclinic representative of both synthetic and natural layered double hydroxides (LDHs) based on octahedrally coordinated di- and trivalent metal cations. It occurs in hydrothermal veins in the Kovdor alkaline massif, Kola peninsula, Russia. The structure was solved by direct methods and refined to R1 = 0.031 on the basis of 304 unique reflections. It is monoclinic, space group C2/m, a = 5.266(2), b = 9.114(2), c = 7.766(3) Å, β = 103.17(3)º, V = 362.9(2) Å3. The diffraction pattern of quintinite-1M contains sharp reflections corresponding to the layer stacking sequence characteristic of the 3R rhombohedral polytype, and rows of weak superlattice reflections superimposed upon a background of streaks of modulated diffuse intensity parallel to c*. These superlattice reflections indicate the formation of a 2-D superstructure due to Mg-Al ordering. The structure consists of ordered metal hydroxide layers and a disordered interlayer. As the unit cell contains exactly one layer, the polytype nomenclature dictates that the mineral be called quintinite-1M. The complete layer stacking sequence can be described as ...=Ac1B=Ba1C=Cb1A=... Quintinite-1M is isostructural with the monoclinic polytype of [Li2Al4(OH)12](CO3)(H2O)3.

Crystal chemistry of natural layered double hydroxides. 3. The crystal structure of Mg,Al-disordered quintinite-2H

Abstract Two crystals of Mg, Al-disordered quintinite-2H (Q1 and Q2), [Mg4Al2(OH)12](CO3)(H2O)3, from the Kovdor alkaline massif, Kola peninsula, Russia, have been characterized chemically and structurally. Both crystals have hexagonal symmetry, P63/mcm, a = 3.0455(10)/3.0446(9), c = 15.125(7)/15.178(5) Å, V = 121.49(8)/121.84(6) Å3. The structures of the two crystals have been solved by direct methods and refined to R1 = 0.046 and 0.035 on the basis of 76 and 82 unique observed reflections for Q1 and Q2, respectively. Diffraction patterns obtained using an image-plate area detector showed the almost complete absence of superstructure reflections which would be indicative of the Mg-Al ordering in metal hydroxide layers, as has been observed recently for other quintinite polytypes. The crystal structures are based on double hydroxide layers [M(OH)2] with an average disordered distribution of Mg2+ and Al3+ cations. Average bond lengths for the metal site are 2.017 and 2.020 Å for Q1 and Q2, respectively, and are consistent with a highly Mg-Al disordered, average occupancy. The layer stacking sequence can be expressed as ...=AC=CA=..., corresponding to a Mg-Al-disordered 2H polytype of quintinite. The observed disorder is probably the result of a relatively high temperature of formation for the Q1 and Q2 crystals compared to ordered polytypes. This suggestion is in general agreement with the previous observations which demonstrated, for the Mg-Al system, a higher-temperature regime of formation of the hexagonal (or pseudo-hexagonal in the case of quintinite-2H-3c) 2H polytype in comparison to the rhombohedral (or pseudo-rhombohedral in the case of quintinite-1M) 3R polytype.

Nicksobolevite, Cu7(SeO3)2O2Cl6, a new complex copper oxoselenite chloride from Tolbachik fumaroles, Kamchatka peninsula, Russia

Nicksobolevite, ideally Cu7(SeO3)2O2Cl6, was found in a fumarole of the second cinder cone of the North Breach of the Great Fissure Tolbachik volcano eruption (1975–1976), Kamchatka Peninsula, Russia. The mineral occurs as aggregates of red needle-like crystals up to 0.4 mm in maximal dimension, elongated along [001]. Associated minerals are chloromenite, prewittite, melanothallite, sophiite, ralstonite, ponomarevite, and native gold. Nicksobolevite is monoclinic, P 21/ c , a = 10.958(9), b = 14.483(5), c = 10.494(14) A, β = 113.61(7)°, V = 1526(3) A3, Z = 4 (from powder diffraction data). The eight strongest lines of the X-ray powder diffraction pattern are ( I-d-hkl ): 77-8.25-(110); 100-5.877-(120); 26-4.239-(112); 37-3.619-(040); 95-3.257-(310), (321); 50-2.715-(402); 26-2.668-(033), (411); and 40-2.278-(242), 134). Nicksobolevite is dark red, with vitreous luster and orange-red streak. The mineral is very brittle and transparent. Cleavage is perfect on {010} and {−101} and good on {120}. The Mohs hardness measured by microindentation is 2–2½. The calculated density is 4.18 g/cm3 (based on the empirical chemical formula). Nicksobolevite is optically positive, with α = 2.00(1), β = 2.01(1), γ = 2.08(1), 2Vcalc. = 43°, and the orientation is X = b , Z^c = 36° (in obtuse β). Pleochroism: X , Y = red, Z = brownish red. The chemical composition determined by the electron-microprobe analysis is (wt. %): CuO 56.17, ZnO 2.34, SeO2 23.29, Cl 22.69, O = Cl −5.13, total 99.36. The empirical formula of nicksobolevite, calculated on the basis of 14 anions per formula unit, is (Cu6.71Zn0.27)∑6.98Se1.99O7.92Cl6.08. The simplified formula is Cu7(SeO3)2O2Cl6, which requires CuO 59.02, SeO2 23.52, Cl 22.54, O = Cl −5.09, total 100.00 wt%. The crystal structure was solved by direct methods and refined to an agreement index R 1 = 0.075 on the basis of 3590 independent observed reflections. The structure contains eight symmetrically independent Cu2+ positions with coordination numbers varying from 5 to 6. The crystal structure is based upon [O4Cu13] tetramers consisting of four corner-sharing OCu4 tetrahedra. The tetrahedra are surrounded by the Se1O3 and Se2O3 selenite triangular pyramids to form linear {[O4Cu13](SeO3)4} complexes oriented parallel to [210] and [−210] and linked to each other into layers with a ladder-like configuration. The layers are perpendicular to the a axis and are surrounded by Cl− anions, which provide their linkage in the [100] direction. The mineral is named in honor of Academician Nikolay (Nick) Vladimirovich Sobolev (b. 1935), in recognition of his important contributions to mineralogy and petrology. Nicksobolevite is the most structurally complex and Cl-rich copper selenite chloride known so far.

Crystal structure of cis-[PdCl2(CNMes)2]

The interaction between PdCl2(CH3CN)2 and 2,4,6-Me3C6H2NC (MesNC) proceeds with the substitution of acetonitrile ligands and leads to the synthesis of a cis-[PdCl2(MesNC)2] complex. The structure of this compound is determined by single crystal X-ray diffraction (XRD). The complex has a slightly distorted square-planar structure of the metal center with two cis-positioned isocyanide ligands. In both CN isocyanide moieties the triple bonds have lengths similar to the lengths of the respective bonds in other isocyanide complexes. In the structure, the cis-[PdCl2(MesNC)2] complexes are bound by weak С–H∙∙∙Cl hydrogen bonds and π-stacking interactions.

Crystal chemistry and nomenclature of the lovozerite group

The paper summarizes crystal-chemical data and describes the IMA-accepted nomenclature of lovozerite-group minerals (LGM). The lovozerite group includes nine zeolite-like cyclosilicates with the general formula A3B3C2MSi6O12O6� x(OH)xnH2O, with species-defining M ¼ Zr, Ti, Fe 3þ , Ca; C ¼ Ca, Mn 2þ , Na, &; A ¼ Na, Ca; B ¼ Na, & ;0 � x � 6; n ¼ 0-1. Their structures are based upon a heteropolyhedral framework consisting of rings of Si-centred tetrahedra and M-centred octahedra forming a 3D system of channels that host A, B, and C cations. The structures can be also considered as based upon pseudocubic modules centred at the midpoint of the Si tetrahedral ring. The M, A, and B cations are located at the borders of the module, whereas C cations are inside the module. The modules are stacked in three different arrangements in LGM allowing distinction of three subgroups: (1) zirsinalite-lovozerite subgroup (includes cation-saturated combeite, kapustinite, kazakovite and zirsinalite, and cation-deficient litvinskite, lovozerite and tisinalite), (2) koashvite subgroup (incl. koashvite) and (3) imandrite subgroup (incl. imandrite). The nature of cation-deficient LGM is discussed. The calculation scheme for empirical formulae of LGM and the criteria of definition of a mineral species (end-members) in the group are given.

New nickel-uranium-arsenic mineral species from the oxidation zone of the Belorechenskoye deposit, Northern Caucasus, Russia: I. Rauchite, Ni(UO2)2(AsO4)2·10H2O, a member of the autunite group

Rauchite, ideally Ni(UO 2 ) 2 (AsO 4 ) 2 ·10H 2 O (IMA no. 2010-037), a new arsenate mineral species of the autunite group, was found at the Belorechenskoye deposit, Adygea Republic, Northern Caucasus, Russia. It is a supergene mineral associated with dymkovite, annabergite and goethite in cavities of a dolomite vein with primary uraninite (pitchblende), nickeline and gersdorffite. Rauchite forms pseudo-tetragonal lamellar crystals (the main form is {001}) up to 0.5 mm across, typically split, like a fan or open book, and their clusters or crusts as large as 2 mm. Rauchite is transparent to translucent and light yellowish-green. The lustre is vitreous. The mineral is brittle, the Mohs’ hardness is ca. 2. The cleavage is {001} perfect. D calc is 3.427 g cm −3 . Rauchite is optically biaxial (−), α = 1.550(3), β = 1.578(1), γ = 1.581(1), 2 V meas = 40(5)°, 2 V calc = 36°. The average chemical composition (mean of eight electron-microprobe analyses) is (in wt%): MgO = 0.71, CoO = 0.07, NiO = 5.38, ZnO = 0.08, P 2 O 5 = 1.08, As 2 O 5 = 20.26, UO 3 = 54.22, H 2 O calc = 17.10, and the total = 98.90. The empirical formula calculated on the basis of 22 O apfu is: (Ni 0.76 Mg 0.19 Co 0.01 Zn 0.01 ) ∑ 0.97 U 2.00 O 4 (As 1.86 P 0.16 ) ∑2.02 O 8 ·10H 2 O. Rauchite is triclinic, space group I -1, a = 7.100(3), b = 7.125(3), c = 19.955(8) A, α = 92.406(14), β = 94.924(14), γ = 90.420(6)°, V = 1004.7(7) A 3 , Z = 2. [parameters of the reduced P cell are: a = 7.100(3), b = 7.125(3), c = 10.751(4) A, α = 106.855(7), β = 104.366(7), γ = 90.420(6)°, V = 502.4(4) A 3 , Z = 1]. The crystal structure was refined from single-crystal X-ray diffraction data obtained at 153 K ( R 1 = 0.089). The structure is based upon autunite-type [(UO 2 )[AsO 4 ]] − layers with Ni 2+ coordinated by six H 2 O molecules and located in the interlayer space. The strongest lines in the powder X-ray diffraction pattern are [ d in A( I )( hkl )]: 9.97(100)(002), 6.641(22)(003), 4.936(62)(004, 01-3, −111), 4.533(41)(−112), 3.539(93)(020, 200, 20-1, 01-5, 02-1), 3.388(43)(20-2, 015, 02-2, 105), 2.488(27)(220, 2-21, −125, 1-25, 22-2, −222), and 2.233(27)(1-31, 3-10, 13-1, 31-1, 31-2, 2-24, 13-2, 21-7). The structure of rauchite corresponds to the 1 A -type stacking arrangement of uranyl arsenate layers in the autunite group of minerals and synthetic compounds. The mineral is named in accordance with the naming rules accepted for the autunite group as the hydrated analogue of metarauchite, Ni(UO 2 ) 2 (AsO 4 ) 2 ·8H 2 O.

Zinc(II)-mediated generation of 5-amino substituted 2,3-dihydro-1,2,4-oxadiazoles and their further ZnII-catalyzed and O2-involving transformations

ZnII-activated cyanamides NCNR2 (R2 = Me2, Et2, C5H10, (CH2)2O(CH2)2, Ph2) react with the acyclic N-alkyl ketonitrones Ph2CN+(O−)R′ (R′ = Me, CH2Ph) and N-aryl ketonitrones (R′ = Ph, p-BrC6H4, p-EtC6H4) under mild conditions. Uncomplexed 5-aminosubstituted 2,3-dihydro-1,2,4-oxadiazoles (6 examples; 49–82%) were obtained in zinc(II)-involving cycloaddition of the N-alkyl ketonitrones to the cyanamide substrates; these 2,3-dihydro-1,2,4-oxadiazoles undergo ring-opening giving carbamoylamidines and methylidenureas. The N-aryl ketonitrones react with ZnII-activated cyanamides giving the open-chain systems, viz. carbamoylamidines, N′-(2-(diphenylmethylidene)amino)-phenyl-N,N-carbamimidic acids, and methylidenureas, which are presumably formed via the cycloaddition route followed by the N–O cleavage induced by the acceptor character of the aryl groups.

Zvyaginite, NaZnNb2Ti[Si2O7]2O(OH,F)3(H2O)4 + x (x < 1), a new mineral of the epistolite group from the Lovozero Alkaline Pluton, Kola Peninsula, Russia

A new mineral, zvyaginite, a member of the epistolite group, has been found at Mt. Malyi Punkaruaiv, Lovozero Alkaline Complex, Kola Peninsula, Russia. It occurs in a hydrothermally altered peralkaline pegmatite and is associated with ussingite, microcline, aegirine, sphalerite, vigrishinite, and sauconite. Zvyaginite forms rectangular or irregular-shaped lamellae up to 0.1 × 1 × 2 cm in size when flattened [001]. The mineral is translucent to transparent and colorless, pearly-white, yellowish brownish, pale pink, or violet pink. The luster is nacreous on crystal faces and greasy on broken surfaces. Its Mohs’ hardness is 2.5–3. Zvyaginite is brittle. The cleavage parallel to {001} is perfect. Dmeas = 2.88(3), Dcalc = 2.94 g/cm3. The mineral is optically biaxial (−), α = 1.626(5), β = 1.714(3), γ = 1.740(5), 2Vmeas = 45(15)°, 2Vcalc = 55°. The IR spectrum is given. Chemical composition is as follows (wt %; average of five point analyses; H2O was determined using the modified Penfield method): 4.74 Na2O, 0.22 K2O, 0.77 CaO, 1.36 MnO, 0.24 FeO, 9.61 ZnO, 0.19 Al2O3, 29.42 SiO2, 12.33 TiO2, 27.22 Nb2O5, 1.94 F, 12.65 H2O, −0.82 −O = F2, for a total of 99.87. The empirical formula calculated on the basis of Si + Al = 4 is: Na1.24K0.04Ca0.11Mn0.16Fe0.03Zn0.96Nb1.66Ti1.25(Si3.97Al0.03)Σ4O15.07(OH)2.10F0.83(H2O)4.64. The simplified formula is: NaZnNb2Ti[Si2O7]2O(OH,F)3(H2O)4 + x (x < 1), Zvyaginite is triclinic,