Threefold Rotation Axis Research Articles

Cover Feature: A Homoleptic Diphosphatetrahedrane Nickel(0) Complex (Z. Anorg. Allg. Chem. 19/2022)

A three-bladed windmill illustrates the molecular structure of the title complex tris(diphosphatetrahedrane)nickel(0). The three sails of the windmill represent the three diphosphatetrahedrane molecules, which coordinate via their P–P bonds to a single nickel(0) atom forming the windshaft. The three blades illustrate the threefold rotation axis of the complex and the propeller twist of the ligands, which makes the complex chiral.(DOI: 10.1002/zaac.202200124).

Rietveld refinement of the langbeinite-type phosphate K2Ni0.5Hf1.5(PO4)3.

Polycrystalline potassium nickel(II) hafnium(IV) tris-(orthophosphate), a langbeinite-type phosphate, was synthesized by a solid-state method. The three-dimensional framework of the title compound is built up from two types of [MO6] octa-hedra [the M sites are occupied by Hf:Ni in ratios of 0.754 (8):0.246 (8) and 0.746 (8):0.254 (8), respectively] and [PO4] tetra-hedra are connected via O vertices. The K+ cations are located in two positions within large cavities of the framework, having coordination numbers of 9 and 12. The Hf, Ni and K sites lie on threefold rotation axes, while the P and O atoms are situated in general positions.

Topological phase transition in the layered magnetic compound MnSb2Te4 : Spin-orbit coupling and interlayer coupling dependence

Based on the first-principles calculations and theoretical analysis, we investigate the electronic structures, topological phase transition (TPT) and topological properties of layered magnetic compound MnSb2Te4. It has the similar crystal and magnetic structure as the magnetic topological insulator MnBi2Te4. We find that when the spin-orbit coupling (SOC) is considered, the band structure of MnSb2Te4 in antiferromagnetic (AFM) state has no band inversion at {\Gamma}. This is due to the SOC strength of Sb is less than that of Bi. The band inversion can be realized by increasing the SOC of Sb by 0.3 times, which drives MnSb2Te4 from a trivial AFM insulator to an AFM topological insulator (TI) or axion insulator. Uniaxial compressive strain along the layer stacking direction is another way to control the band inversion. The interlayer distance shorten by 5% is needed to drive the similar TPT. For the ferromagnetic (FM) MnSb2Te4 with experimental crystal structure, it is a normal FM insulator. The band inversion can happen when SOC is enhanced by 0.1 times or the interlayer distance is decreased by more than 1%. Thus, FM MnSb2Te4 can be tuned to be the simplest type-I Weyl semimetal with only one pair of Weyl nodes on the three-fold rotational axis. These two Weyl nodes are projected onto (1-10) surface with one Fermi arc connecting them.

Tris[N,N-bis-(3,5-di-tert-butyl-benz-yl)di-thio-carbamato-κ2 S,S']-μ3-sulfido-tris-μ2-disulfido-triangulo-trimolybdenum(IV) iodide.

The title compound, [Mo3(C31H46NS2)3S7]I, crystallizes on a threefold rotational axis in P31c (space group No. 159). The [Mo3S7(S2CN(CH2C6H3-3,5- t Bu2)2)3]+ cations are arrayed in sheets in the ab plane with inter-ligand hydro-phobic inter-actions between tert-butyl groups guiding the packing arrangement. These cations form stacks parallel to the c axis with a separating distance of 10.9815 (6) Å (the c axis length) between the Mo3 centroids. On the underside of the cluster, opposite the μ3-S2- ligand, the iodide counteranion forms close contacts of 3.166 (2) Å with the sulfur atoms of the μ2-S2 2- ligands. These contacts are less than the sum of the van der Waals radii of the atoms (1.8 and 2.1 Å for S and I, respectively), thus indicating an appreciable degree of covalency to the [Mo3S7(S2CN(CH2C6H3-3,5- t Bu2)2)3]+⋯I- inter-actions.

Towards a Solution of the A-B-Z Question using Z-Disks Isolated from the Flight Muscle of Lethocerus Indicus

The recent publication of a 3-D image of isolated Z-disks from Apis mellifera, flight muscle[Rusu et al., J. Muscle Res Cell Motil (2017)], the first of its kind utilizing isolated Z-disks, confirmed many details of the previously 3-D image obtained from plastic sections[Cheng and Deatherage, J. Cell Biol. (1989)]. However, they used relatively harsh treatment of high KCl/KI to isolate Z-disks. Here we combine 1.4M NaCl and 10mM pyrophosphate applied to Lethocerus indicus flight muscle to remove the thick filaments and 4.5min exposure to calcium insensitive gelsolin to remove the thin filaments from the remaining of the I-Z-I-brushes. We are improving the resolution by adding more tilt-series to our previous analysis. By comparing the Fourier transforms and subvolume averages, we conclude that Z-disks from honey-bee and Lethocerus indicus are similar but not identical. The large solvent channel that characterizes the honey-bee Z-disk is less prominent in Lethocerus, which is reflected in a much weaker to nearly absent 1,0 spot intensity in transforms of Lethocerus Z-disks, whereas the corresponding spots in the honey-bee transform are strong. There is ample evidence that the actin filaments in the overlap zone of both bee and waterbug flight muscle present a helical array of target zones around each thick filament. However, Squire[J. Molec. Biol. 72, (1972)] has pointed out that the P312 symmetry assumed for the honey-bee Z-disk reconstruction from plastic sections when extrapolated into the A-band, implies rings rather than helices of target zones surrounding the thick filament. This discrepancy might be resolved if there are three-fold screw axes instead of three-fold rotation axes at the lattice and trigonal positions of the flight muscle Z-band; corresponding more to space group symmetry P3121.

Crystal structure of poly[[hexa-aqua-tris-(μ-3,6-di-oxo-cyclo-hexa-1,4-diene-1,4-diolato)dierbium(III)] octa-deca-hydrate

The title lanthanide complex, [Er2(C6H2O4)3(H2O)6]·18H2O, is isostructural with its La, Gd, Yb and Lu analogues. The Er3+ ion, located on a threefold rotation axis, is nine-coordinated in a distorted tricapped trigonal-prismatic geometry, which is completed by six oxygen atoms from three dhbq2- ligands and three oxygen atoms from coordinated water mol-ecules. Each dhbq2- ligand acts in a μ2-bis-(bidentate) bridging mode to connect two Er3+ ions to form honeycomb (6,3) two-dimensional sheets extending in the ab plane, having an Er⋯Er separation of 8.7261 (2) Å. In the crystal, extensive O-H⋯O hydrogen-bonding inter-actions involving the coordinated water mol-ecules and the water mol-ecules of crystallization, as well as the oxygen atoms of the dhbq2- ligands, generate an overall three-dimensional supra-molecular network.

Crystal structures of 2-bromo-1,1,1,3,3,3-hexa-methyl-2-(tri-methyl-sil-yl)tris-ilane and 2-bromo-1,1,1,3,3,3-hexa-isopropyl-2-(triiso-propyl-sil-yl)tri-silane.

The synthesis and crystal structures of two tris-(tri-alkyl-sil-yl)silyl bromide compounds, C9H27BrSi4 (I, HypSiBr) and C27H63BrSi4 (II, TipSiBr), are described. Compound I was prepared in 85% yield by free-radical bromination of 1,1,1,3,3,3-hexa-methyl-2-(tri-methyl-sil-yl)tris-ilane using bromo-butane and 2,2'-azobis(2-methyl-propio-nitrile) as a radical initiator at 333 K. The mol-ecule possesses threefold rotational symmetry, with the central Si atom and the Br atom being located on the threefold rotation axis. The Si-Br bond distance is 2.2990 (12) Å and the Si-Si bond lengths are 2.3477 (8) Å. The Br-Si-Si bond angles are 104.83 (3)° and the Si-Si-Si bond angles are 113.69 (2)°, reflecting the steric hindrance inherent in the three tri-methyl-silyl groups attached to the central Si atom. Compound II was prepared in 55% yield by free-radical bromination of 1,1,1,3,3,3-hexa-isopropyl-2-(triiso-propyl-sil-yl)tris-ilane using N-bromo-succinimide and 2,2'-azobis(2-methyl-propio-nitrile) as a radical initiator at 353 K. Here the Si-Br bond length is 2.3185 (7) Å and the Si-Si bond lengths range from 2.443 (1) to 2.4628 (9) Å. The Br-Si-Si bond angles range from 98.44 (3) to 103.77 (3)°, indicating steric hindrance between the three triiso-propyl-silyl groups.

Poly[bis(trimethylammonium) [hexa-μ-cyanido-cadmium(II)dicopper(I)

The title compound, {(C3H10N)2[CdCu2(CN)6]}n, has been synthesized as an alternative to the high-emitting complexes containing more expensive metals. The CN−ligands make linkages between the CuIand CdIIions to form the coordination polymer, [CdCu2(CN)6]n2−, which is a three-dimensional framework classified as pyrite net (pyr). The net has a void space for accommodating a trimethylammonium ion located on a threefold rotation axis. The CdIIion lies on a special position with site symmetry -3 and is octahedrally coordinated by six N atoms. The CuIion is located on a threefold rotation axis and has a trigonal-planar coordination geometry formed by three C atoms. In the three-dimensional net, two CuIions are arranged closely [Cu...Cu = 3.9095 (5) Å], but the distance is not short enough to suggest a CuI–CuIinteraction. The crystal studied was a merohedral twin (twin operation 2[101]), the refined component ratio being 0.9202 (7):0.0798 (7). A powder of the title compound shows strong luminescence with an emission maximum at 509 nm and a quantum yield of 98% at room temperature.

A Polyselenide with a Novel Se78– Unit: the Structure of Sr19–xPbxGe11Se44 with x = 5.0 and 6.4

An unprecedented, planar Se78– unit with a threefold rotation axis was discovered in the new polyselenide Sr19–xPbxGe11Se44. Sr12.6Pb6.4Ge11Se44 crystallizes in the non‐centrosymmetric hexagonal space group P63 with unit cell dimensions of a = b = 19.9867(2) Å, c = 12.0546(1) Å, V = 4170.28(7) Å3, with two formula units per cell. Its structure contains isolated [GeSe4] tetrahedra, [Ge2Se7] dimers, and a novel, planar propeller‐shaped Se78– unit. The latter is unprecedented, but reminiscent of the isoelectronic pyramidal Se78– and I7– units. It consists of a central Se atom, to which three Se2 pairs with a short Se–Se bond are attached through a longer Se–Se distance, resulting in a central Se atom featuring 120° bond angles, and bridging Se atoms featuring an approximately linear coordination with a 179° bond angle. It can thus be written as [Se(Se2)3]8–. We characterized this unit using Gaussian calculations in comparison to the pyramidal Se78– unit, which may be described also as [Se(Se2)3]8–. The solid‐state material is a black semiconductor with an optical band‐gap of 1.8 eV, which supports the assignment of this charge.

A [Cu3(μ3-O)]-pyrazolate metallacycle with terminal nitrate ligands exhibiting point group symmetry 3.

The trinuclear triangular cuprate anion of the title compound, tris-[bis-(tri-phenyl-phospho-ranyl-idene)ammonium] tris-(μ2-4-chloro-pyrazolato-κ(2) N:N')-μ3-oxido-tris-[(nitrato-κ(2) O,O')cuprate(II)] nitrate monohydrate, (C36H30P2N)[Cu3(C3H2ClN2)3(NO3)3O]NO3·H2O, has point group symmetry 3., with the μ3-O atom located on the threefold rotation axis. The distorted square-pyramidal coordination sphere of the Cu(II) atom is completed by two N atoms of trans-bridging pyrazolate groups and a chelating nitrate anion. The complex anion is slightly bent, with the nitrate and pyrazolate groups occupying positions above and below the Cu3 plane, respectively. In the crystal, weak O-H⋯O and C-H⋯O hydrogen bonds, as well as π-π inter-actions, are present.

Crystal structure of tri-hydrogen bis-{[1,1,1-tris-(2-oxido-ethyl-amino-meth-yl)ethane]-cobalt(III)} trinitrate.

The title compound, [Co2(L)2]3+·3NO3 − [where L = CH3C(CH2NHCH2CH2OH1/2)3], has been synthesized from the ligand 1,1,1-tris­(2-hy­droxy­ethyl­amino­meth­yl)ethane. The cobalt(III) dimer has an inter­esting and uncommon O—H⋯O hydrogen-bonding motif with the three bridging hy­droxy H atoms each being equally disordered over two positions. In the dimeric trication, the octa­hedrally coordinated CoIII atoms and the capping C atoms lie on a threefold rotation axis. The N atoms of two crystallographically independent nitrate anions also lie on threefold rotation axes. N—H⋯O hydrogen bonding between the complex cations and nitrate anions leads to the formation of a three-dimensional network structure. The compound is a racemic conglomerate of crystals containing either d or l mol­ecules. The crystal used for this study is a d crystal.

Crystal structure of tris-(hydroxyl-ammonium) orthophosphate.

The crystal structure of the title salt, ([H3NOH]+)3·[PO4]3−, consists of discrete hydroxyl­ammonium cations and ortho­phos­phate anions. The atoms of the cation occupy general positions, whereas the anion is located on a threefold rotation axis that runs through the phospho­rus atom and one of the phosphate O atoms. In the crystal structure, cations and anions are linked by inter­molecular O—H⋯O and N—H⋯O hydrogen bonds into a three-dimensional network. Altogether, one very strong O—H⋯O, two N—H⋯O hydrogen bonds of medium strength and two weaker bifurcated N—H⋯O inter­actions are observed.

Crystal structure of an unknown solvate of dodecakis-(μ2-alaninato-1:2κ(2) O:N,O)cerium(III)hexa-nickel(II) aqua-tris-(hydroxido-κO)tris-(nitrato-κ(2) O,O')cerate(III).

The chiral title compound, [CeNi6(C3H6NO2)12][Ce(NO3)3(OH)3(H2O)], comprises a complex heterometallic Ni/Ce cation and a homonuclear Ce anion. Both the cation and anion exhibit point group symmetry 3. with the CeIII atom situated on the threefold rotation axis. The cation metal core consists of six NiII atoms coordinated in a slightly distorted octa­hedral N2O4 configuration by N and O atoms of 12 deprotonated l-alaninate ligands exhibiting both bridging and chelating modes. This metal–organic coordination motif encapsulates one CeIII atom that shows an icosa­hedral coordination by the O-donor atoms of the l-alaninate ligands, with Ce—O distances varying in the range 2.455 (5)–2.675 (3) Å. In the anion, the central CeIII ion is bound to three bidentate nitrate ligands, to three hydroxide ligands and to one water mol­ecule, with Ce—O distances in the range 2.6808 (19)–2.741 (2) Å. The H atoms of the coordinating water mol­ecule are disordered over three positions due to its location on a threefold rotation axis. Disorder is also observed in fragments of two l-alaninate ligands, with occupancy ratios of 0.608 (14):0.392 (14) and 0.669 (8):0.331 (8), respectively, for the two sets of sites. In the crystal, the complex cations and anions assemble through O—H⋯O and N—H⋯O hydrogen bonds into a three-dimensional network with large voids of approximately 1020 Å3. The contributions of highly disordered ethanol and water solvent mol­ecules to the diffraction data were removed with the SQUEEZE procedure [Spek (2015 ▸). Acta Cryst. C71, 9–18]. The given chemical formula and other crystal data do not take into account the unknown amount of these solvent mol­ecules.

Crystal structure of tris-(1,3-dimesityl-4,5-di-hydro-1H-imidazol-3-ium) tetra-bromido-cobaltate(II) bromide chloro-form hexa-solvate.

In the unit cell of the title compound, (C21H27N2)3[CoBr4]Br·6CHCl3, the tetrabromidocobaltate(II) anion and the bromide anion are located on a crystallographic threefold rotation axis. For the [CoBr4]2− group, the axis runs through one of the Br ligands and the CoII atom. All other structure moieties lie on general sites. Various tris­(1,3-dimesityl-4,5-di­hydro-1H-imidazol-3-ium) structures with different counter-ions have been reported. In the title compound, the N—C—N angle is 113.7 (5)°, with short C—N bond lengths of 1.297 (7) and 1.307 (7) Å. The two mesityl planes make a dihedral angle of 34.6 (1)° and the dihedral angles between the mesityl and N–C–N planes are 82.0 (1) and 88.5 (1)°, respectively. The imidazoline ring is almost planar, with atom deviations in the range 0.003 (5)–0.017 (5) Å from the best plane; the mean deviation is 0.012 (5) Å. In the crystal, non-covalent inter­actions of the C—H⋯Br type occur between the Br− anion and the cation, as well as between the [CoBr4]2− anion and both the chloro­form solvent mol­ecules. These H⋯A distances are slightly shorter than the sum of van der Waals radii.

Crystal structure of Sc1.91In1.39Mo15Se19, containing Mo6 and Mo9 clusters.

The structure of scandium indium penta-deca-molybdenum nona-deca-selenide, Sc1.91In1.39Mo15Se19, is isotypic with In2.9Mo15Se19 [Grüttner et al. (1979 ▸). Acta Cryst. B35, 285-292]. It is characterized by two cluster units Mo6Se (i) 8Se (a) 6 and Mo9Se (i) 11Se (a) 6 (where i represents inner and a apical atoms) that are present in a 1:1 ratio. The cluster units are centered at Wyckoff positions 2b and 2c and have point-group symmetry -3 and -6, respectively. The clusters are inter-connected through additional Mo-Se bonds. Sc-Se and In-Se bonds complete the structural set-up. In the title compound, the Sc(3+) cations replace the trivalent indium atoms present in In2.9Mo15Se19, and a deficiency is observed at the monovalent indium site. One Mo, one Se and the Sc atom are situated on mirror planes, whereas two other Se atoms and the In atom are situated on threefold rotation axes.

Cover Picture: Dinuclear Face-Sharing Bi-octahedral Tungsten(VI) Core and Unusual Thermal Behavior in Complex Th Tungstates (Chem. Eur. J. 21/2015)

A rare case of a confacial bi-octahedral tungsten(VI) core was isolated from a thorium tungstate system. These compounds are constructed from a complex polyoxometalate-like cage and exhibit unexpected thermal behavior. Interestingly, the cage with a threefold rotation axis passing through its center has a cross-section remarkably similar to a six-leafed lily. A comprehensive discussion can be found in the Full Paper by E. V. Alekseev et al. on page 7746 ff. A rare case of a confacial bi-octahedral tungsten(VI) core was isolated from a thorium tungstate system. These compounds are constructed from a complex polyoxometalate-like cage and exhibit unexpected thermal behavior. Interestingly, the cage with a threefold rotation axis passing through its center has a cross-section remarkably similar to a six-leafed lily. A comprehensive discussion can be found in the Full Paper by E. V. Alekseev et al. on page 7746 ff. Trifluoromethylation In the Minireview on page 7648 ff., Y.-M. Liang and co-workers describe the recent efforts in the development of trifluoromethylation of alkyne reactions by radical processes, or transition-metal catalysis using nucleophilic or electrophilic trifluoromethylation reagents. Various diverse C(sp, sp2, sp3)CF3 bonds were easily constructed in moderate to good yields under mild conditions. Although the above achievements have been obtained, several limitations still remain in the trifluoromethylation reactions of alkynes.1 Functionalization of Boron Nitride Platelets of hexagonal boron nitride were functionalized with a silicon oxide rim in a simple room-temperature process. The mechanism of this functionalization has been investigated by first principles calculations. More details of this research are reported by R. Nesper and co-workers in their Communication on page 7662 ff.1 Polyoxometalates The reaction of early lanthanides, GeO2, and Na2WO4 in buffered medium was systematically studied and a series of hexameric and dodecameric polyoxometalates with a closely related crown-shaped framework based on [Ln2GeW10O38]6– Keggin-type subunits was isolated. The dodecamers represent the first macroions with dual behavior in the formation of vesicle-like structures that lead to different supramolecular assemblies in terms of composition and size by a solvent-triggered skeletal modification of the species undergoing self-association. For more details, see the Full Paper by S. Reinoso et al. on page 7736 ff.1

Na-Ca carbonates synthesized under upper-mantle conditions: Raman spectroscopic and X-ray diffraction studies

The new Na4Ca(CO3)3, Na2Ca3(CO3)4 and Na2Ca4(CO3)5 compounds were synthesized in the system Na2CO3–CaCO3 in multianvil experiments at 6 GPa and characterized by Raman spectroscopy. In addition, the Na2Ca3(CO3)4 compound was studied using in situ energy dispersive and single-crystal X-ray diffraction. Single bands in the CO32− symmetric stretching region ( v1 ) and out-of-plane bending region ( v2 ) in the Na4Ca(CO3)3 Raman spectrum suggest a single crystallographically distinct carbonate group in the structure. In contrast, the spectra of Na2Ca3(CO3)4 and Na2Ca4(CO3)5 show two and three bands, respectively, in both the symmetric stretching region ( v1 ) and out-of-plane bending region ( v2 ), suggesting more than one crystallographically distinct carbonate group in the unit cell. Raman activity in the forbidden v2 mode and multiple bands are observed in the in-plane bending region ( v4 ) for the three compounds, proving the reduction of site symmetry of the CO32− ions with the loss of the threefold rotation axis ( D 3h → D 2h or C s). Such a decrease in symmetry suggests distortion of the group itself, but may be attained by rearrangements of the coordinated metal cations as in the aragonite-group carbonates. At 6.5 GPa and 1000°C, the structure of Na2Ca3(CO3)4 was found to be orthorhombic or monoclinic with a β angle close to 90° and the lattice parameters: a = 7.3357(6) A, b = 8.0377(9) A, and c = 31.5322 (32) A, with V = 929.59(14) A3. No structural changes were observed during pressure decrease down to 1 GPa, while a discontinuous increase in unit-cell parameters and volume was observed upon decompression from 1 GPa at room temperature. This indicates a pressure-induced phase transition to a structurally related ambient-pressure phase. The abnormally long c -parameter and proximity of the β-angle to 90° of Na2Ca3(CO3)4 at ambient conditions suggest that, in the monoclinic system, the metric symmetry is higher than the Laue symmetry, which is a common sign for merohedral twinning.

Lack of a threefold rotation axis in α-Fe₂O₃ and α-Cr₂O₃ crystals.

The crystal structure of α-Fe2O3 and α-Cr2O3 is usually described with the corundum-type trigonal crystal structure based on the space group R3¯c. There are, however, some observations of the magnetic ordering of both α-Fe2O3 and α-Cr2O3 that are incompatible with the trigonal symmetry. We show experimental evidence based on X-ray powder diffraction and supported by transmission electron microscopy that the symmetry of the crystal structure of both α-Fe2O3 and α-Cr2O3 is monoclinic and it is described with the space group C2/c (derived from R3¯c by removing the threefold rotation axis). The magnetic orderings of α-Fe2O3 and α-Cr2O3 are compatible with the magnetic space groups C2/c and C2/c', respectively. These findings are in agreement with the idea from Curie [(1894), J. Phys. 3, 393-415] that the dissymmetry of the magnetic ordering should be associated with a dissymmetry of the crystal structure.

Crystal structure of the co-crystal fac-tri-aqua-tris(thio-cyanato-κN)iron(III)-2,3-di-methyl-pyrazine (1/3).

In the crystal of the title compound, [Fe(NCS)3(H2O)3]·3C6H8N2, the Fe(III) cation is located on a threefold rotation axis and is coordinated by three N atoms of the thiocyanate anions and three water mol-ecules in a fac arrangement, forming a slightly distorted N3O3 octa-hedron. Stabilization within the crystal structure is provided by O-H⋯N hydrogen bonds; the H atoms from coordinating water mol-ecules act as donors to the N atoms of guest 2,3-di-methyl-pyrazine mol-ecules, leading to a three-dimensional supra-molecular framework.

About the polymorphism of [Li(C4H8O)3]I: crystal structures of trigonal and tetra-gonal polymorphs.

Two new trigonal and tetra-gonal polymorphs of the title compound, iodido-tris-(tetra-hydro-furan-κO)lithium, are presented, which both include the isolated ion pair Li(THF)3 (+)·I(-). One Li-I ion contact and three tetra-hydro-furan (THF) mol-ecules complete the tetra-hedral coordination of the lithium cation. The three-dimensional arrangement in the two polymorphs differs notably. In the trigonal structure, the ion pair is located on a threefold rotation axis of space group P-3 and only one THF mol-ecule is present in the asymmetric unit. In the crystal, strands of ion pairs parallel to [001] are observed with an eclipsed conformation of the THF mol-ecules relative to the Li⋯I axis of two adjacent ion pairs. In contrast, the tetra-gonal polymorph shows a much larger unit cell in which all atoms are located on general positions of the space group I41 cd. The resulting three-dimensional arrangement shows helical chains of ion pairs parallel to [001]. Apart from van der Waals contacts, no remarkable inter-molecular forces are present between the isolated ion pairs in both structures.