Kyzylkumite, Ti2V3+O5(OH): new structure type, modularity and revised formula

The crystal structure of kyzylkumite, ideally Ti2V3+O5(OH), from the Sludyanka complex in South Baikal, Russia was solved and refined (including the hydrogen atom position) to an agreement index, R1, of 2.34 using X-ray diffraction data collected on a twinned crystal. Kyzylkumite crystallizes in space group P21/c, with a = 8.4787(1), b = 4.5624(1), c = 10.0330(1) Å, β = 93.174(1)°, V = 387.51(1) Å3 and Z = 4. Tivanite, TiV3+O3OH, and kyzylkumite have modular structures based on hexagonal close packing of oxygen, which are made up of rutile TiO2 and montroseite V3+O(OH) slices. In tivanite the rutile:montroseite ratio is 1:1, in kyzylkumite the ratio is 2:1. The montroseite module may be replaced by the isotypic paramontroseite V4+O2 module, which produces a phase with the formula Ti2V4+O6. In the metamorphic rocks of the Sludyanka complex, vanadium can be present as V4+ and V3+ within the same mineral (e.g. in batisivite, schreyerite and berdesinskiite). Kyzylkumite has a flexible composition with respect to the M4+/M3+ ratio. The relationship between kyzylkumite and a closely related Be-bearing kyzylkumite-like mineral with an orthorhombic norbergite-type structure from Byrud mine, Norway is discussed. Both minerals have similar X-ray powder diffraction patterns.

Crystal chemistry and hydrogen bonding of rustumite Ca10(Si2O7)2(SiO4)(OH)2Cl2 with variable OH, Cl, F

Three samples of the skarn mineral rustumite Ca10(Si2O7)2(SiO4)(OH)2Cl2, space group C2/c, a ≈7.6, b ≈ 18.5, c ≈ 15.5 Å, β ≈ 104°, with variable OH, Cl, F content were investigated by electron microprobe, single-crystal X-ray structure refinements, and Raman spectroscopy. “Rust1LCl” is a low chlorine rustumite Ca10(Si2O7)2(SiO4)(OH1.88F0.12)(Cl1.28,OH0.72) from skarns associated with the Rize batholith near Ikizedere, Turkey. “Rust2F” is a F-bearing rustumite Ca10(Si2O7)2(SiO4)(OH1.13F0.87) (Cl1 96OH0.04) from xenoliths in ignimbrites of the Upper Chegem Caldera, Northern Caucasus, Russia. “Rust3LClF” represents a low-Cl, F-bearing rustumite Ca10(Si2O7)2(SiO4)0.87(H4O4)0.13(OH1.01F0.99) (Cl1.00 OH1.00) from altered merwinite skarns of the Birkhin massif, Baikal Lake area, Eastern Siberia, Russia. Rustumite from Birkhin massif is characterized by a significant hydrogarnet-like or fluorine substitution at the apices of the orthosilicate group, leading to specific atomic displacements. The crystal structures including hydrogen positions have been refined from single-crystal X-ray data to R1 = 0.0205 (Rust1_LCl), R1 = 0.0295 (Rust2_F), and R1 = 0.0243 (Rust3_LCl_F), respectively. Depletion in Cl and replacement by OH is associated with smaller unit-cell dimensions. The substitution of OH by F leads to shorter hydrogen bonds O-H⋯F instead of O-H⋯OH. Raman spectra for all samples have been measured and confirm slight strengthening of the hydrogen bonds with uptake of F.This study discusses the complex crystal chemistry of the skarn mineral rustumite and may provide a wider understanding of the chemical reactions related to contact metamorphism of limestones.

In situ dehydration behavior of veszelyite (Cu,Zn)2Zn(PO4)(OH)3·2H2O: A single-crystal X-ray study

The rare mixed copper-zinc phosphate mineral veszelyite (Cu,Zn)2Zn(PO4)(OH)3·2H2O space group P21/c, a = 7.5096(2), b = 10.2281(2), c = 9.8258(2) Å, β = 103.3040(10)°, V = 734.45(3) Å3 was investigated by in situ temperature-dependent single-crystal X-ray structure refinements. The atomic arrangement of veszelyite consists of an alternation of octahedral and tetrahedral sheets. The Jahn-Teller distorted CuO6 octahedra form sheets with eight-membered rings. The tetrahedral sheet composed of PO4 and ZnO3(OH) tetrahedra shows strong topological similarities to that of cavansite, gismondine, and kipushite.Diffraction data of a sample from Zdravo Vrelo, near Kreševo (Bosnia and Herzegovina) have been measured in steps of 25 up to 225 °C. Hydrogen positions and the hydrogen-bond system were determined experimentally from the structure refinements of data collected up to 125 °C. At 200 °C, the hydrogen-bonding scheme was inferred from bond-valence calculations and donor-acceptor distances. The hydrogen-bond system connects the tetrahedral sheet to the octahedral sheet and also braces the Cu sheet.At 150 °C, the H2O molecule at H2O2 was released and the Cu coordination (Cu1 and Cu2) decreased from originally six- to fivefold. Cu1 has a square planar coordination by four OH groups and an elongate distance to O3, whereas Cu2 has the Jahn-Teller characteristic elongate bond to H2O1. The unit-cell volume decreased 7% from originally 734.45(3) to 686.4(4) Å3 leading to a formula with 1 H2O pfu. The new phase observed above 150 °C is characterized by an increase of the c axis and a shortening of the b axis. The bending of T-O-T angles causes an increasing elliptical shape of the eight-membered rings in the tetrahedral and octahedral sheets. Moreover a rearrangement of the hydrogen-bond system was observed.At 225 °C, the structure degrades to an X-ray amorphous residual due to release of the last H2O molecule at H2O1. The stronger Jahn-Teller distortion of Cu1 relative to Cu2 suggests that Cu1 is fully occupied by Cu, whereas Cu2 bears significant Zn. H2O1 is the fifth ligand of Cu2. Zn at Cu2 is not favorable to adopt planar fourfold coordination. Thus, if the last water molecule is expelled the structure is destabilized.This study contributes to understanding the dehydration mechanism and thermal stability of supergene minerals characterized by Jahn-Teller distorted octahedra with mixed Cu, Zn occupancy.

Superspace description of wagnerite-group minerals (Mg,Fe,Mn) 2 (PO 4 )(F,OH)

Reinvestigation of more than 40 samples of minerals belonging to the wagnerite group (Mg, Fe, Mn)2(PO4)(F,OH) from diverse geological environments worldwide, using single-crystal X-ray diffraction analysis, showed that most crystals have incommensurate structures and, as such, are not adequately described with known polytype models (2b), (3b), (5b), (7b) and (9b). Therefore, we present here a unified superspace model for the structural description of periodically and aperiodically modulated wagnerite with the (3+1)-dimensional superspace group C2/c(0[beta]0)s0 based on the average triplite structure with cell parameters a [asymptotically equal to] 12.8, b [asymptotically equal to] 6.4, c [asymptotically equal to] 9.6 Å, [beta] [asymptotically equal to] 117° and the modulation vectors q = [beta]b*. The superspace approach provides a way of simple modelling of the positional and occupational modulation of Mg/Fe and F/OH in wagnerite. This allows direct comparison of crystal properties.

Interaction of the Trinuclear Triangular Secondary Building Unit [Cu 3 (μ 3 -OH)(μ-pz) 3 ] 2+ with 4,4′-Bipyridine. Structural Characterizations of New Coordination Polymers and Hexanuclear Cu II Clusters. 2°

By reacting 4,4′-bipyridine (bpy) with selected trinuclear triangular CuII complexes, [Cu3(μ3-OH)(μ-pz)3(RCOO)2(LL′)] [pz = pyrazolate anion; R = CH3, CH3CH2, CH2═CH, CH2═C(CH3); L, L′ = Hpz, H2O, MeOH] in MeOH, the substitution of monotopic ligands by ditopic bpy was observed. Depending on the stoichiometric reaction ratios, different compounds were isolated and structurally characterized. One- and two-dimensional coordination polymers (CPs), as well as two hexanuclear CuII clusters were identified. One of the hexanuclear clusters self-assembles into a supramolecular three-dimensional structure, and its crystal packing shows the presence of two intersecting channels, one of which is almost completely occupied by guest bpy, while in the second one guest water molecules are present. This compound also shows a reversible, thermally induced, single-crystal-to-single-crystal transition.

Synthesis and Structural Characterizations of New Coordination Polymers Generated by the Interaction Between the Trinuclear Triangular SBU [Cu 3 (μ 3 -OH)(μ-pz) 3 ] 2+ and 4,4′-Bipyridine. 3°

The reactions of 4,4′-bipyridine with selected trinuclear triangular copper(II) complexes, [Cu3(μ3-OH)(μ-pz)3(RCOO)2Lx], [pz = pyrazolate anion, R = CH3(CH2)n (2 ≤ n ≤ 5); L = H2O, MeOH, EtOH] yielded a series of 1D coordination polymers (CPs) based on the repetition of [Cu3(μ3-OH)(μ-pz)3] secondary building units joined by bipyridine. The CPs were characterized by conventional analytical methods (elemental analyses, ESI-MS, IR spectra) and single crystal XRD determinations. An unprecedented 1D CP, generated through the bipyridine bridging hexanuclear copper clusters moieties, two 1D CPs presenting structural analogies, and two monodimensional tapes having almost exactly superimposable structures, were obtained. In one case, the crystal packing makes evident the presence of small, not-connected pores, accounting for ca. 6% of free cell volume.