Sevenfold Coordination Research Articles

The crystal and molecular structure of (R)-sirtinol – C26H22N2O2 – a chemo-sensitive enhancer and ligand in metal complexes with important bio-inorganic applications

Abstract Sirtinol is a known inhibitor of sirtuin proteins – a family of deacetylases involved in the physiology of aging. Its crystalline structure has never been determined except when bound to Fe(III) where it participates in the seven-fold coordination of the metal or to Cu(II) where it acts as a bidentate or tridentate ligand. Herein, we describe the structure of this important molecule, as follows: (a) the prevalent form of the keto-enol tautomerism in the solid state, and (b) in solution. Do they match? If not, how? The crystals of (R)-sirtinol are characterized by a large number of π–π bonded interactions linking molecules in infinite ribbons, which, in turn, are linked by additional π–π interactions of a variety of types, and by hydrogen bonds. In the latter case, we confirm by NMR that the X-ray determined position of an important H atom is on a N atom rather than on an O, which is how the molecule is usually depicted.

Markwelchite, TlPbSbS3, a new Tl–Pb sulfosalt from the hydrothermal deposit of Jas Roux, Hautes-Alpes, France

AbstractMarkwelchite, ideally TlPbSbS3, is a new mineral from the hydrothermal deposit of Jas Roux, Hautes-Alpes, France. It occurs as a black anhedral crystal associated closely with protochabournéite. Microhardness measurements (VHN15) gave a mean value of 197 kg/mm2 corresponding to a Mohs hardness of ~3–4. In plane-polarised incident light, markwelchite is grey in colour. Under crossed polars, it is distinctly anisotropic with greyish white to bluish rotation tints, with bright red internal reflections. Reflectance percentages (Rmin and Rmax) are: 28.5, 31.5 (471.1 nm); 28.3, 30.7 (548.3 nm); 27.9, 30.3 (586.6 nm); and 27.6, 29.8 (652.3 nm). The mean of 5 electron microprobe spot analyses gave Tl 34.67(45), Pb 31.86(25), Sb 15.06(15), As 2.37(5), S 15.35(20), total 99.31 wt.%, corresponding, on the basis of a total of 6 atoms per formula unit and structural results, to Tl1.063Pb0.964(Sb0.775As0.198)Σ0.973S3.000. Single-crystal X-ray diffraction studies revealed that markwelchite is isotypic with richardsollyite, TlPbAsS3. It is monoclinic, space group P21/c, with the following unit-cell parameters: a = 8.9144(3), b = 8.4513(3), c = 8.6511(3) Å, β = 108.723(4)°, V = 617.27(4) Å3 and Z = 4. The five strongest observed powder-diffraction lines [d in Å (Irel)(hkl)] are: 3.88 (100)($\bar{2}$11); 3.78 (90)(210); 3.29 (90)(102); 2.73 (85)($\bar{1}$13); and 2.93 (75)(022). The crystal structure can be described as formed by (100) [Me2(SbS3)]– layers sandwiching the Me1+ cations. The Me1 site has a seven-fold coordination, whereas the Me2 site has an 6+2 coordination corresponding to a distorted, bicapped trigonal prismatic coordination, and the Sb site displays a trigonal pyramidal coordination with three S atoms and Sb at the apex.The name markwelchite honours Dr Mark D. Welch of the Natural History Museum, London, UK.The new mineral has been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2024–001). A discussion on the relationships between markwelchite and synthetic TlPbSbS3 is also provided.

Lithium and sodium 3-(3,4-di-hydroxy-phen-yl)propenoate hydrate.

Treatment of 3-(3,4-di-hydroxy-phen-yl)propenoic acid (caffeic acid or 3,4-di-hydroxy-cinnamic acid) with the alkali hydroxides MOH (M = Li, Na) in aqueous solution led to the formation of poly[aqua-[μ-3-(3,4-di-hydroxy-phen-yl)propenoato]lithium], [Li(C9H7O4)(H2O)]n, 1, and poly[aqua-[μ-3-(3,4-di-hydroxy-phen-yl)propenoato]sodium], [Na(C9H7O4)(H2O)]n, 2. The crystal structure of 1 consists of a lithium cation that is coordinated nearly tetra-hedrally by three carboxyl-ate oxygen atoms and a water mol-ecule. The carboxyl-ate groups adopt a μ3-κ3 O:O':O' coordination mode that leads to a chain-like catenation of Li cations and carboxyl-ate units parallel to the b axis. Moreover, the lithium carboxyl-ate chains are connected by hydrogen bonds between water mol-ecules attached to lithium and catechol OH groups. The crystal structure of 2 shows a sevenfold coordination of the sodium cation by one water mol-ecule, two monodentately binding carboxyl-ate groups and four oxygen atoms from two catechol groups. The coordination polyhedra are linked by face- and edge-sharing into chains extending parallel to the b axis. The chains are inter-linked by the bridging 3-(3,4-di-hydroxy-phen-yl)propenoate units and by inter-molecular hydrogen bonds to form the tri-periodic network.

Synthesis and crystal structure of two scandium oxotellurates(IV): Sc2Te3O9 and Sc2Te4O11

Abstract The two new scandium oxotellurates(IV) Sc2Te3O9 and Sc2Te4O11 were synthesized through firing appropriate mixtures of Sc2O3, TeO2 and CsBr (as flux) in evacuated glassy silica ampoules at 850 °C for 10 days. Both of them crystallize in the monoclinic space group P21/c with Z = 4 (Sc2Te3O9: a = 523.36(3), b = 2438.23(14), c = 731.98(4) pm, β = 116.221(3)°; Sc2Te4O11: a = 949.51(6), b = 779.12(5), c = 1341.93(9) pm, β = 90.829(3)°). Both crystal structures contain two crystallographically unique Sc3+ cations. In the case of Sc2Te3O9, they reside in six- and sevenfold oxygen coordination arranged as distorted uncapped or capped octahedra, while for Sc2Te4O11, they only exhibit six oxygen atoms in the coordination polyhedra, but one of them has also a certain tendency to thrive for a higher coordination number (C.N. = 6 + 1). The [(Sc1)O6)]9− and [(Sc2)O6+1)]11− polyhedra in Sc2Te3O9 are condensed via common edges to form serrated ∞ 1 { [ Sc 2 O 6 / 1 t O 1 / 2 v O 4 / 2 e ] 11 − } ${\text{ }}_{\infty }^{1}\left\{{\left[{\text{Sc}}_{2}{\text{O}}_{6\text{/}1}^{\text{t}}{\text{O}}_{1\text{/}2}^{\text{v}}{\text{O}}_{4\text{/}2}^{\text{e}}\right]}^{11-}\right\}$ chains running along [100], whereas the two [ScO6]9− octahedra in Sc2Te4O11 only share common vertices, generating ∞ 1 { [ Sc 2 O 6 / 1 t O 3 / 2 v ] 9 − } ${\text{ }}_{\infty }^{1}\left\{{\left[{\text{Sc}}_{2}{\text{O}}_{6\text{/}1}^{\text{t}}{\text{O}}_{3\text{/}2}^{\text{v}}\right]}^{9-}\right\}$ double strands along [010]. In both compounds, the three-dimensional framework and the charge balance are accomplished by the discrete ψ1-tetrahedral [TeO3]2− anions with non-bonding lone-pair electrons located at their central Te4+ cations. Moreover, strong secondary Te4+···O2− interactions, which are generally quite common for rare earth metal(III) oxotellurates(IV), occur in both crystal structures, but much more pronounced in Sc2Te4O11, where three quarters of the Te4+ cations reside in the centers of ψ eq 1 ${{\psi}}_{\text{eq}}^{1}$ -trigonal bipyramids [TeO4]4− as compared to Sc2Te3O9, which can well be written as Sc2[TeO3]3.

Structure and properties of two new heteroleptic bismuth(III) dithiocabamates of the general composition Bi(S2CNH2)2X (X = Cl, SCN)

Abstract The title compounds were prepared by precipitation from acidic solutions of the reactants in acetone/water. Bi(S2CNH2)2Cl (1) crystallizes in the non-centrosymmetric trigonal space group P32 with a = 8.6121(3) and c = 11.1554(4) Å, Z = 3; Bi(S2NH2)2SCN (2) in P21/c (monoclinic) with a = 5.5600(2), b = 14.3679(5), c = 12.8665(4) Å, and β = 90.37(3)°. In the crystal structure of 1 Bi3+ is in a sevenfold coordination of two bidentate and one monodentate S2CHNH2 − anions with an asymmetric coordination pattern of five Bi–S and two Bi–Cl− bonds. The linkage of these polyhedra via common Cl–S edges leads to a 1D polymeric structure with undulated chains propagating in the direction [001]. These chains are linked by strong and medium strong hydrogen bonds forming the 3D crystal structure. In the crystal structure of 2 the Bi3+ cation is in an eightfold coordination. The polyhedron can be described as a significantly distorted tetragonal anti-prism, capped by an additional S atom. Two of these prisms share a common quadrilateral face to form a “prism-double” (Bi2S10N2). These building units are linked by common edges, and the resulting 1D infinite angulated chains propagate along [100]. By contrast to organo-dithiocarbamate compounds, where C–H···X bridges are dominant, the interchain connections in the crystal structures of 1 and 2 are formed exclusively via N–H···S, N–H···Cl, and N–H···N interactions, generating the 3D networks. A significant eccentricity of the Bi3+ cation in the crystal structures of both complexes is observed. Both compounds emit light in the orange range of the electromagnetic spectrum.

Experimental and first-principles studies on photoluminescence of Ce3+-doped calcium chloroborate Ca2BO3Cl

The luminescense properties of Ce3+ ions in Ca2BO3Cl were studied upon excitation in the 3–20 eV range. It is shown that because of the presence of different charge compensating defects, the various types of centers involving Ce3+ are formed in Ca2BO3Cl. Based on the results obtained, the values of the crystal field splitting and the centroid shift of the Ce3+ 5d configuration for locally uncompensated Ce3+ centers were determined and compared with those of Ce3+ ions in some other inorganic compounds. The DFT calculations were utilized to study the band structure of Ca2BO3Cl, the 4f→5d transitions of Ce3+ ions and the intrinsic defects of this compound. The calculated band gap of Ca2BO3Cl (7.22 eV) is consistent with the experimental value of 7.35 eV, and the 4f→5d transition energies for Ce3+ ions on the two sevenfold coordination sites confirm spectral assignments based on the luminescent measurements. The experimental results and first-principles calculations show that the introduction of Na+ hardly influences the luminescence properties of Ce3+-doped Ca2BO3Cl. The possible processes occurring in Ca2BO3Cl:Eu2+, Ce3+ persistent phosphors are also discussed based on the combined theoretical and experimental results.

Compressibility and Phase Stability of Iron-Rich Ankerite

The structure of the naturally occurring, iron-rich mineral Ca1.08(6)Mg0.24(2)Fe0.64(4)Mn0.04(1)(CO3)2 ankerite was studied in a joint experimental and computational study. Synchrotron X-ray powder diffraction measurements up to 20 GPa were complemented by density functional theory calculations. The rhombohedral ankerite structure is stable under compression up to 12 GPa. A third-order Birch–Murnaghan equation of state yields V0 = 328.2(3) Å3, bulk modulus B0 = 89(4) GPa, and its first-pressure derivative B’0 = 5.3(8)—values which are in good agreement with those obtained in our calculations for an ideal CaFe(CO3)2 ankerite composition. At 12 GPa, the iron-rich ankerite structure undergoes a reversible phase transition that could be a consequence of increasingly non-hydrostatic conditions above 10 GPa. The high-pressure phase could not be characterized. DFT calculations were used to explore the relative stability of several potential high-pressure phases (dolomite-II-, dolomite-III- and dolomite-V-type structures), and suggest that the dolomite-V phase is the thermodynamically stable phase above 5 GPa. A novel high-pressure polymorph more stable than the dolomite-III-type phase for ideal CaFe(CO3)2 ankerite was also proposed. This high-pressure phase consists of Fe and Ca atoms in sevenfold and ninefold coordination, respectively, while carbonate groups remain in a trigonal planar configuration. This phase could be a candidate structure for dense carbonates in other compositional systems.

Dot Nanopattern Self‐Assembled from Rod‐Coil Block Copolymer on Substrate

AbstractNanoscale dot patterns are important in various fields. However, it is still a challenge to fabricate ordered nanopatterns on substrates through a polymer self‐assembly approach. In this work, it is reported that polypeptide‐based rod‐coil block copolymers can self‐assemble into surface micelles on substrates, thus forming dot nanopatterns. The size of the surface micelles is readily adjusted by the degree of the polymerization of the block copolymers. It is found that most of the surface micelles are in a sixfold coordinated lattice, indicating an ordered array feature. Defects such as fivefold coordination arrays and sevenfold coordination arrays are also observed, which are derived from the nonuniform size of the micelles and the existence of nonspherical micelles. The experimental findings are well modelled by dissipative particle dynamics theoretical simulations, and the simulations provide more detailed information, such as the packing manner of the polymer chain in the surface micelles.

Electronic structure, thermodynamic stability and high-temperature sensing properties of Er-\u03b1-SiAlON ceramics

α-SiAlON ceramics have been in use as engineering ceramics in the most arduous industrial environments such as molten metal handling, cutting tools, gas turbine engines, extrusion molds, thermocouple sheaths, protective cover for high-temperature sensors, etc., owing to their outstanding mechanical, thermal and chemical stability. Taking advantage of the intrinsic properties of α-SiAlONs, we investigate, in this paper, the possibility of using the Er-doped α-SiAlON (Er-α-SiAlON) ceramic as a high-temperature sensing material via its unique near-infrared to visible upconversion property. We first use neutron diffraction and density functional theory calculations to study the electronic structure and thermodynamic stability of Er-α-SiAlON. It is found that the interstitial doping of Er stabilizes the α-SiAlON structure via chemical bonds with O-atoms with N:O ratio of 5:2 in the seven-fold coordination sites of the Er3+ ion. Temperature-dependent upconversion emissions are then studied under 980 and 793 nm excitations over a temperature range of 298–1373 K and the fluorescence intensity ratio (FIR) technique has been employed to investigate the temperature sensing behavior. Temperature-dependent Raman behavior is also investigated. We demonstrate that using Er-α-SiAlON as a sensing material, the limit of temperature measurement via the FIR technique can be pushed well beyond 1200 K.

Ordered Surface Nanostructures Self-Assembled from Rod-Coil Block Copolymers on Microspheres.

An ordered surface nanostructure endows materials advanced functions. However, fabricating ordered surface-patterned particles via the polymer self-assembly approach is a challenge. Here we report that poly(γ-benzyl-l-glutamate)-block-poly(ethylene glycol) rod-coil block copolymers are able to form uniform-surface micelles on polystyrene microspheres through a solution self-assembly approach. The size of the surface micelles can be varied by the molecular weight of the block copolymers. These surface micelles are arranged in a manner consistent with the Euler theorem. Most of the micelles are six-fold coordinated, and the number difference between the five-fold and the seven-fold coordination is 12. Simulations on model systems qualitatively reproduced the experimental findings and provided direct observations for the surface-patterned particles, including the polymer chain packing manner in surface micelles at the molecular level and the array feature of the surface micelles through 2D projections of the surface patterns.

Molecular aggregations of bicyclodioxazastannone produced from multicomponent reactions involving functionalized 2-hydroxybenzaldehydes, α- or β-amino acids and a dimethyltin precursor

A series of novel bicyclodioxazastannone derived from ONO Schiff base ligands prepared from diazenylaryl functionalized 2-hydroxybenzaldehydes and α or β-amino acetates, viz., [Me2Sn(L1)]2 (1), [Me2Sn(L2)]2 (2), [Me2Sn(L3)(MeOH)]2 (3), [Me2Sn(L4)]n (4), [Me2Sn(L5)]n⋅nH2O (5), [Me2SnL6)]2 (6), [Me2Sn(L7)] (7A), [Me2Sn(L7)]2⋅C8H10 (7B) and [Me2Sn(L8)]n (8), with variously substituted Schiff bases L1-L8 generated in situ, were synthesized and structurally characterized. The crystal structures of compounds 1–8 revealed different structure types with five-, six- or seven-fold coordination of the metal center. Except for 7A, which crystallized in the form of a discrete mononuclear tin complex, intermolecular association through O→Sn interactions was observed. The resulting aggregates were molecular dimers with a central four-membered Sn2O2 ring (1, 2, 6 and 7A), 1D coordination polymers (4, 5 and 8) and a solvent adduct linked through both O–H⋅⋅⋅O hydrogen bonds and O⋅⋅⋅Sn contacts (3). In the presence of hydrogen bond donors such as O–H and N–H groups in the ligands, the molecular structures are further interconnected through O/N–H⋅⋅⋅O hydrogen bonds, giving in combination with the O⋅⋅⋅Sn contacts overall 2D layer-type assemblies. In solution, contrary to the β-alanine derivative 1, the 1H and 13C NMR spectra of compounds 2–8 displayed signals for the Me2Sn moieties because of diastereotopic environments according to the asymmetric nature of the ligand. The 119Sn NMR data of most of the compounds were acquired in DMSO‑d6 with the chemical shift displacements indicating six-coordinate tin atoms, which is in good agreement with the O→Sn adduct formation in the solid-state structures. The 119Sn NMR spectrum of compound 2 measured in CDCl3 indicates the presence of a mononuclear tin complex, as expected for a non-coordinating solvent.

Quaternary rare-earth selenides Ba2REGaSe5 and Ba2REInSe5

Twelve quaternary rare-earth selenides Ba2REGaSe5 and Ba2REInSe5 were prepared in the form of single crystals from reactions of BaSe, RE, M2Se3 (M = Ga, In), and Se at 1373 K. The compounds Ba2REGaSe5 fall into two separate series adopting an orthorhombic (RE = La, Ce; space group Pnma, Z = 4, a = 12.49–12.50 Å, b = 9.60–9.63 Å, c = 8.74 Å) or a triclinic structure (RE = Tb, Ho, Tm, Yb, Lu; space group P1¯, Z = 2, a = 7.28–7.31 Å, b = 8.61–8.72 Å, c = 9.37–9.43 Å, α = 103.4–103.5°, β = 103.0–103.1°, γ = 107.3–107.5°). The compounds Ba2REInSe5 adopt an orthorhombic structure (RE = Pr, Tb, Ho, Tm, Lu; space group Cmc21, Z = 4, a = 4.23–4.33 Å, b = 18.75–18.96 Å, c = 13.29–13.31 Å). All structures contain anionic M-centred tetrahedra, isolated Se2– anions, Ba2+ cations in eight-fold coordination, and RE3+ cations in either six- or seven-fold coordination. A structure map developed based on radius ratios involving the RE3+, M3+, and Ch2– ions is effective in segregating four structures (in space groups Cmc21, P1¯, Pnma, and I4/mcm) found for Ba2REMCh5 (M = Ga, In; Ch = S, Se, Te). Bond valence sum calculations reveal that the upper limit for the largest RE components that can be substituted within a given structural series is set by the need to avoid overbonding of the RE atoms. An optical band gap of 1.34(2) eV was measured for the compound Ba2LaGaSe5, slightly less than a value of 1.76 eV obtained from electronic band structure calculations, which suggest an indirect transition.

High-density amorphous phase of CdO

An amorphous CdO model is densified up to a theoretical pressure of 200GPa. A continues phase transformation from a low-density amorphous (LDA) phase to a high-density amorphous (HDA) phase is observed through the simulation. Associated with the phase transformation, the average coordination raises progressively from ~5.5 to ~7.0. The sevenfold coordination is the most abundant motifs in the HDA state. Therefore its short-range order differs principally from that of the known CdO crystals. Upon pressure release, an amorphous state being intermediate between the LDA structure and the HDA phase is recovered with a mean coordination number of 5.9.

First high-pressure synthesis of rossmanitic tourmaline and evidence for the incorporation of Li at the X site

Lithium is an important component of some tourmalines, especially in chemically evolved granites and pegmatites. All attempts at synthesizing Li-rich tourmaline have so far been unsuccessful. Here we describe the first synthesis of rossmanitic tourmaline at 4 GPa and 700 °C in the system Li2O–Al2O3–SiO2–B2O3–H2O (LASBH) from seed-free solid starting materials consisting of a homogenous mixture of Li2O, γ-Al2O3, quartz and H3BO3. The solid run products after 12-day run duration comprise rossmanitic tourmaline (68 wt%), dumortierite (28 wt%) and traces of spodumene (3 wt%) and coesite (1 wt%). Tourmaline forms idiomorphic, large prismatic crystals (30 × 100 μm), which are inclusion free and chemically unzoned. The refined cell dimensions of the tourmaline are: a = 15.7396(9) A, c = 7.0575(5) A, V = 1514.1(2) A3. Conventionally, the Li+ ion is assumed to exclusively occupy the octahedral Y site in the tourmaline structure to a maximum of 2 Li per formula unit (pfu). However, the chemical composition of our synthetic tourmaline determined by electron microprobe and secondary ion mass spectroscopy results in the formula: X(☐0.67(11)Li0.33(11))Y(Al2.53(10)Li0.47(10))Z(Al6)T(Si5.42(15)B0.58(15))O 18 B (BO3) 3 V+W [(OH)2.40(3)O1.60(3)], wherein a significant amount of Li occupies the X site for charge balance requirements. Reliable assignment of the OH-stretching vibrations in a polarized single-crystal Raman spectrum such as a single-crystal XRD structure refinement, confirms the incorporation of Li at the X site [0.24(9) and 0.15(5) XLi pfu, respectively]. The SREF data show that the Li–O1 distances are shortened significantly in order to compensate for the smaller ionic radius of Li+ compared to Na+, K+ or Ca2+ at the X site, i.e., Li is closer to the Si6O18 ring and to a sevenfold coordination with oxygen.

Surface determination through atomically resolved secondary-electron imaging.

Unique determination of the atomic structure of technologically relevant surfaces is often limited by both a need for homogeneous crystals and ambiguity of registration between the surface and bulk. Atomically resolved secondary-electron imaging is extremely sensitive to this registration and is compatible with faceted nanomaterials, but has not been previously utilized for surface structure determination. Here we report a detailed experimental atomic-resolution secondary-electron microscopy analysis of the c(6 × 2) reconstruction on strontium titanate (001) coupled with careful simulation of secondary-electron images, density functional theory calculations and surface monolayer-sensitive aberration-corrected plan-view high-resolution transmission electron microscopy. Our work reveals several unexpected findings, including an amended registry of the surface on the bulk and strontium atoms with unusual seven-fold coordination within a typically high surface coverage of square pyramidal TiO5 units. Dielectric screening is found to play a critical role in attenuating secondary-electron generation processes from valence orbitals.

Synthesis and photoluminescence properties of fluorite-related (Y1−xEux)10W2O21 phosphor

Eu3+-doped fluorite-related yttrium–tungsten oxide Y10W2O21 (5Y2O3·2WO3) was prepared using vibrating-mill-mixed powder and solid-state reactions. The synthesis temperature was investigated by thermogravimetric/differential thermal analysis and X-ray diffraction. The morphology of the phosphor was confirmed by scanning electron microscope (SEM) measurement. The photoluminescence (PL) properties, including the excitation and emission spectra, decay curves (lifetime), thermal stability and quantum efficiency, were investigated. The PL emission intensity was found to increase with Eu3+ content up to about 22.5mol% and then decrease due to the concentration quenching effect. There were two kinds of coordinating site (seven-fold coordination and eight-fold coordination) of Y3+ ions in the fluorite-related structure of Y10W2O21. Eu3+ in different coordinating sites of Y3+ in the host could lead to energy-level splitting of the 5D0→7F2 transition, resulting in an emission peak red shift. The major intensity emission wavelengths, located at 612nm and 627nm for excitation at 392nm, were attributed to replacement of the Eu3+ ions with 7 or 8 coordination sites of Y3+ ions.

Room temperature crystallization of trichlorodioxouranate [UO2Cl3(L)] species in molecular assemblies involving aliphatic dicarboxylate linkers

Three uranyl carboxylates (UO2)2Cl6(succ)·4dmaH (1), (UO2)2Cl6(adip)·4dmaH (2) and (UO2)2Cl6(1,4-chdc)·4dmaH (3) have been synthesized from slow evaporation in ambient atmosphere of solutions of aliphatic carboxylic acids and UCl4 in N,N-dimethyformamide (DMF) after a solvothermal treatment (succ=succinate, adip=adipate, 1,4-chdc=1,4-cyclohexanedicarboxylate, dmaH=monoprotonated dimethylamine). These three compounds possess a similar crystal structure based on the molecular assembly of discrete dinuclear motifs (UO2)2Cl6(L) separated by dimethylammonium cations (coming from the in situ decomposition of DMF). Hexavalent uranium cation is found in seven-fold coordination (pentagonal bipyramid) with the typical double uranyl bond. Three chloride anions and two carboxyl oxygen atoms are located in the equatorial pentagonal plane, resulting in a trichlorodioxouranate ‘UO2Cl3(OC)2’ tecton. The uranyl centers are linked to each other through the ditopic ligand via the two carboxylate arms. The three compounds have been characterized by infrared and luminescence spectroscopies.

M(18-crown-6)X][N(Tf)2] (M: Zn, Co; X: I, N(Tf)2) with unusual crown-ether coordination

[M(18-crown-6)X][N(Tf)2] (M: Zn, Co; X: I, N(Tf)2) is obtained by reacting equimolar amounts of MI2 and 18-crown-6 with an excess of I2 in the ionic liquid [NMe(n-Bu)3]2[N(Tf)2] at 100°C. The cationic complexes [Zn(18-crown-6)I]+ and [Co(18-crown-6)N(Tf)2]+ exhibit an unusual sevenfold coordination of Zn2+/Co2+ and an unusually twisted 18-crown-6 molecule as a ligand. The structural arrangement is ascribed to the small radius of Zn2+/Co2+, the weakly coordinating features of the ionic liquid and the stabilization of the [Zn(18-crown-6)I]+ and [Co(18-crown-6)N(Tf)2]+ cations via hydrogen-bridge bonding.

Unusual sevenfold coordination of Ru in complex hydride Na3RuH7: Prospect for formation of [FeH7]3– anion

We used density-functional calculations to clarify the origin of the unusual sevenfold coordination of Ru by H in Na3RuH7. We found that the D5h symmetry of the ligands enables the formation of strong covalent bonds of Ru and H through ligand-field effects, stabilizing the sevenfold coordination. We also examined the possible synthesis of the hypothetical 3d analog, Li3FeH7, which has a gravimetric hydrogen density of 8.4 mass%. The calculated enthalpy change of −16 kJ/mol H2 for the reaction, 3LiH+Fe+2H2→Li3FeH7, reveals a possible route to a stable complex hydride containing [FeH7]3–.

How calcium inhibits the magnesium‐dependent kinase gsk3β: A molecular simulation study

Glycogen synthase kinase 3β (GSK3β) is a ubiquitous serine/threonine kinase that plays a pivotal role in many biological processes. GSK3β catalyzes the transfer of γ-phosphate of ATP to the unique substrate Ser/Thr residues with the assistance of two natural activating cofactors Mg(2+). Interestingly, the biological observation reveals that a non-native Ca(2+) ion can inhibit the GSK3β catalytic activity. Here, the inhibitory mechanism of GSK3β by the displacement of native Mg(2+) at site 1 by Ca(2+) was investigated by means of 80 ns comparative molecular dynamics (MD) simulations of the GSK3β···Mg(2+)-2/ATP/Mg(2+) -1 and GSK3β···Mg(2+)-2/ATP/Ca(2+)-1 systems. MD simulation results revealed that using the AMBER point charge model force field for Mg(2+) was more appropriate in the reproduction of the active site architectural characteristics of GSK3β than using the magnesium-cationic dummy atom model force field. Compared with the native Mg(2+) bound system, the misalignment of the critical triphosphate moiety of ATP, the erroneous coordination environments around the Mg(2+) ion at site 2, and the rupture of the key hydrogen bond between the invariant Lys85 and the ATP O(β2) atom in the Ca(2+) substituted system were observed in the MD simulation due to the Ca(2+) ion in active site in order to achieve its preferred sevenfold coordination geometry, which adequately abolish the enzymatic activity. The obtained results are valuable in understanding the possible mechanism by why Ca(2+) inhibits the GSK3β activity and also provide insights into the mechanism of Ca(2+) inhibition in other structurally related protein kinases.