Identification of two allotwins of mica polytypes in reciprocal space through the minimal rhombus unit

Nespolo, M.; Ferraris, Giovanni; Takeda, Hiroshi

doi:10.1107/s0108768100002044

Cited by 9 publications

(3 citation statements)

References 21 publications

(28 reference statements)

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“…Although not unknown in molecular crystals, 7−9 2-D lattice compatibility is much more common in polytypic layered inorganic compounds, e.g., mica. 10 The term allotwin 11 was introduced to describe such well-defined mutual orientation of polytypes.…”

Section: Introductionmentioning

confidence: 99%

“…Consequently, stacked layers in the two crystal forms are epitaxially compatible at interfaces where planes of deoxyguanosine moieties interact but not at contacts between planes of iodine atoms. Although not unknown in molecular crystals, − 2-D lattice compatibility is much more common in polytypic layered inorganic compounds, e.g., mica . The term allotwin was introduced to describe such well-defined mutual orientation of polytypes.…”

Section: Introductionmentioning

confidence: 99%

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Polymorphism, Crystal Packing, Twinning, and Molecular Conformations in 5′-Halo-5′-deoxyguanosines and a Hydrate of the Pseudohalide Analogue, 5′-Azido-5′-deoxyguanosine

Parkin

Coldren

Fernandez

et al. 2018

Crystal Growth & Design

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Crystalline 5′-iodo-5′-deoxyguanosine (I) exists as a pair of solvent-free polymorphs (Ia, Ib) and as a mixed water/methanol solvate (Ic). The solvent-free polymorphs are capable of epitaxial intergrowth to give hybrid crystals that by visual inspection appear to be single crystals (Parkin et al. Cryst. Growth Des. 2016, 16, 6343–6352; hereafter PTGB). To investigate the generality and origin of the unusual polymorphism of the solvent-free forms, we have prepared and characterized the 5′-bromo- and 5′-chloro-5′-deoxyguanosine analogues (II and III, respectively), as well as the pseudohalide derivative 5′-azido-5′-deoxyguanosine (IV). Monoclinic and orthorhombic polymorphs of II (IIa and IIb, respectively) and an orthorhombic form of III all grow from water as small nonsolvated, tightly packed needles or laths. Although IIa is isostructural with the dominant polymorph of I (i.e., Ia in PTGB), all of these crystals (IIa, IIb, III) have similar molecular conformations and packing characteristics to Ia, in which the halogen adopts a gauche conformation relative to the deoxyribose ring oxygen. In spite of having different space group symmetries (P21 for Ia and IIa vs P212121 for IIb and III), the crystal structures of IIb and III are also clearly related to Ia. Unlike I, however, no experimental evidence for conformational polymorphism, or of solvated forms was found for either II or III. Similar to PTGB work on I, density functional theory calculations show that the experimental gauche halide-atom conformations in II and III are ∼2.0 kcal/mol higher in energy than the energy-minimized anti-conformation (which occurs in the minor polymorph of I, i.e., Ib). The 5′-azido analogue (IV) in contrast, crystallized solely as a hydrate, initially forming minuscule irregular shards that were far too small for conventional X-ray analysis. By a process of Ostwald ripening, these shards could be enlarged sufficiently to allow structure determination by X-ray crystallography. The hydrate of IV shares many structural characteristics with Ic, but is much more complicated. It contains four independent molecules of IV (i.e., Z′ = 4, vs Z′ = 2 in Ic), which exhibit a range of distinctly different molecular conformations, as well as five full occupancy water molecules.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Polymorphism, Crystal Packing, Twinning, and Molecular Conformations in 5′-Halo-5′-deoxyguanosines and a Hydrate of the Pseudohalide Analogue, 5′-Azido-5′-deoxyguanosine

Parkin

Coldren

Fernandez

et al. 2018

Crystal Growth & Design

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“…The titaniferous oxybiotite from the Ruiz Peak rhyodacite ash flow, Jemez Mountains, New Mexico (Smith et al, 1961;Takeda and Ross, 1975;Bailey and Smith, 1978;Ohta et al, 1982) was the subject of extensive X-ray and HRTEM studies revealing not only all the three basic structures, but also the longest and most complex inhomogeneous polytypes reported to date (Ross et al, 1966;Nespolo and Takeda, 1999;Kogure and Nespolo, 1999a), a large number of twins (about one third of the crystals; Ross and Wones, 1965), and also some allotwins (Nespolo et al, 2000). The composition, rich in ferric iron and titanium, is close to the upper compositional stability limit for oxybiotites.…”

Section: Examples Of Application Of the Perturbative Model To The Ruimentioning

confidence: 99%

Perturbative Theory of Mica Polytypism. Role of the M2 Layer in the Formation of Inhomogeneous Polytypes

Nespolo

2001

Clays and clay miner.

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Abstract--A new model is proposed to explain, within the framework of the theory of spiral growth of Frank, the formation on inhomogeneous mica polytypes. This model relates the interaction and cooperative growth of two components (spirals and/or crystals) to produce a new stacking sequence. Depending on the relative orientation between the two components, a mismatch of the interlayer positions occurs, which is compensated through either a growth defect or a crystallographic slip at the octahedral (O) sheet. Both these adjustments transform the M1 layer into the M2 layer. These two types of layers have the same chemical composition but differ in cation distribution in the O sheet. The coalescence and cooperative growth of crystals occurs in fluid-rich environments and is most frequent in druses and volcanic fumaroles. These environments favor the inhomogeneous polytypes, especially those with complex stacking sequences. In addition, the M1 -~ M2 transformation is most probable in micas with an oxybiotitic composition, where the removal of the OH dipole strengthens the interlayer bonding and the presence of high-charge cations destabilizes the O sheet. Three examples of inhomogeneous polytypes of titaniferous oxybiotite from Ruiz Peak (a volcanic environment where many inhomogeneous polytypes have been reported) are presented.

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The chromatic symmetry of twins and allotwins

Nespolo

2019

Acta Cryst Sect A

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The symmetry of twins is described by chromatic point groups obtained from the intersection group H Ã of the oriented point groups of the individuals H i extended by the operations mapping different individuals. This article presents a revised list of twin point groups through the analysis of their groupoid structure, followed by the generalization to the case of allotwins. Allotwins of polytypes with the same type of point group can be described by a chromatic point group like twins. If the individuals are all differently oriented, the chromatic point group is obtained in the same way as in the case of twins; if they are mapped by symmetry operation of the individuals, the chromatic point group is neutral. If the same holds true for some but not all individuals, then the allotwin can be seen as composed of twinned regions described by a twin point group, that are then allotwinned and described by a colour identification group; the allotwin is then described by a chromatic group obtained as an extension of the former by the latter, and requires the use of extended symbols reminiscent of the extended Hermann-Mauguin symbols of space groups. In the case of allotwins of polytypes with different types of point groups, as well as incomplete (allo)twins, a chromatic point group does not reveal the full symmetry: the groupoid has to be specified instead.

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Identification of two allotwins of mica polytypes in reciprocal space through the minimal rhombus unit

Cited by 9 publications

References 21 publications

Polymorphism, Crystal Packing, Twinning, and Molecular Conformations in 5′-Halo-5′-deoxyguanosines and a Hydrate of the Pseudohalide Analogue, 5′-Azido-5′-deoxyguanosine

Polymorphism, Crystal Packing, Twinning, and Molecular Conformations in 5′-Halo-5′-deoxyguanosines and a Hydrate of the Pseudohalide Analogue, 5′-Azido-5′-deoxyguanosine

Perturbative Theory of Mica Polytypism. Role of the M2 Layer in the Formation of Inhomogeneous Polytypes

The chromatic symmetry of twins and allotwins

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