Regular Octahedral Coordination Research Articles

Experimental and theoretical studies of new Co(III) complexes of hydrazide derivatives proposed as multi-target inhibitors of SARS-CoV-2.

Cobalt(III) complexes with Schiff base ligands derived from hydrazone, (HL 1 = (E)‐N′‐(3,5‐dichloro‐2‐hydroxybenzylidene)‐4‐hydroxybenzohydrazide, HL 2 = (E)‐N′‐(3,5‐dichloro‐2‐hydroxybenzylidene)‐4‐hydroxybenzohydrazide (3,5‐dibromo‐2‐hydroxybenzylidene), and HL 3 = (E)‐4‐hydroxy‐N′‐(2‐hydroxy‐3‐ethoxybenzylidene)benzohydrazide), were synthesized and characterized by elemental analysis, Fourier transform infrared (FT‐IR) spectroscopy, UV–Vis spectroscopy, and cyclic voltammetry. X‐ray diffraction was used to determine the single crystal structure of the complex (1). Co(III) was formed in a distorted, very regular octahedral coordination in this complex; three pyridine moieties complete this geometry. Schiff base complexes' redox behaviors are represented by irreversible (1), quasi‐reversible (2), and quasi‐reversible (3) voltammograms. A density functional theory (DFT)/B3LYP method was used to optimize cobalt complexes with a base set of 6‐311G. Furthermore, fragments occupying the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were investigated at the same theoretical level. Quantum theory of atoms in molecules (QTAIM) computations were also done to study the coordination bonds and non‐covalent interactions in the investigated structures. Hirshfeld surface analysis was used to investigate the nature and types of intermolecular exchanges in the crystal structure of the complex (1). The capacity of cobalt complexes to bind to the major protease SARS‐CoV‐2 and the molecular targets of human angiotensin‐converting enzyme‐2 (ACE‐2) was investigated using molecular docking. The molecular simulation methods used to assess the probable binding states of cobalt complexes revealed that all three complexes were stabilized in the active envelope of the enzyme by making distinct interactions with critical amino acid residues. Interestingly, compound (2) performed better with both molecular targets and the total energy of the system than the other complexes.

Bismuth/Silver-Based Two-Dimensional Iodide Double and One-Dimensional Bi Perovskites: Interplay between Structural and Electronic Dimensions

New structures with favorable band structure and optical properties are of broad interest to the halide perovskite community. Recently, lead-free two-dimensional (2D) double perovskites have emerged as dimensionally reduced counterparts of their 3D analogues. Besides the structural diversity provided by the organic cation, the achievement of 2D lead-free iodide double perovskites has attached researchers to explore more structures in this new material family. Here, we report the synthesis and structures of a series of 2D iodide double perovskites based on cyclic diammonium cations (aminomethyl)piperidinium (AMP) and (aminomethyl)pyridinium (AMPY), (4AMP)2AgBiI8 and (3AMPY)2AgBiI8, and compare them with 1D structures with Bi only (x-AMP)BiI5 and (x-AMPY)BiI5 (x = 3 and 4). The crystallographic structures of the double perovskite phases are highly distorted, because of the inability of Ag to form regular octahedral coordination with iodine. The experimental bandgaps of the double perovskite phases are surprisingly similar ((4AMP)2AgBiI8) or even larger ((3AMPY)2AgBiI8) than in the 1D structures with the same cations ((4AMP)BiI5 and (3AMPY)BiI5). DFT calculations suggest that the effective electronic dimensionality of the double perovskites is on par or lower than that of 1D structures. The reduced electronic dimension of the 2D compounds originates from the weak electronic coupling between the corner-sharing Ag and Bi octahedra. The band structures for the 1D compounds are dispersive in the chain direction, suggesting that their electronic and structural dimensions are similar. Low frequency Raman spectra exhibit distinct peaks at room temperature for all compounds reported here, suggesting rigid lattices

Cd2+ incorporation in small-pore LEV/ERI intergrown zeolites: A multi-methodological study

Small-pore zeolites are successfully employed as catalysts, sorbents and molecular sieves. Their physiochemical properties can be tuned by modifying their extraframework cation (EF) composition via ion exchange. In this study, we investigate the crystal structure of a Cd-exchanged levyne ( LEV ) intergrown with erionite ( ERI ) by combining Single Crystal X-ray Diffraction (SCXRD), Molecular Dynamic simulations (MD) and Extended X-ray Absorption Fine-Structure spectroscopy (EXAFS). Data obtained from the different techniques consistently indicate that Cd 2+ in LEV is arranged in a nearly ordered fashion. In contrast, strong disorder of the EF species (Cd 2+ and H 2 O) is observed in the ERI cavities. Here, Cd 2+ forms aqueous complexes that are more mobile in comparison to LEV , where Cd 2+ bonds to both H 2 O and framework-oxygen atoms. The formation of Cd-clusters is excluded based on EXAFS analysis. Finally, to discriminate between thermal and static disorder, we propose a new approach based on combined MD and geometry optimization. • The crystal structure of Cd-LEV and Cd-ERI was determined by SCXRD. • Cd 2+ has a fairly regular octahedral coordination in Cd-LEV. • Cd 2+ is strongly disordered in the eri cavity. • Cd aqueous complexes form in Cd-ERI. • The disorder of the EF species was resolved by combining MD simulations and XAFS.

Crystal Chemistry of Alkali–Aluminum–Iron Sulfates from the Burnt Mine Dumps of the Chelyabinsk Coal Basin, South Urals, Russia

Technogenic steklite, KAl(SO4)2, and unnamed mineral phase (K,Na)3Na3(Fe,Al)2(SO4)6 from burnt dumps of the Chelyabinsk Coal Basin have been investigated by single-crystal X-ray diffraction and electron microprobe analysis. Steklite is trigonal, space group P3¯, a = 4.7277(3), c = 7.9871(5) Å, V = 154.60(2) Å3. The crystal structure was refined to R1 = 0.026 (wR2 = 0.068). It is based upon the [Al(SO4)2]− layers formed by corner sharing of SO4 tetrahedra and AlO6 polyhedra. The anionic [Al(SO4)2]− layers are parallel to the (001) plane and linked via interlayer K+ ions. The regular octahedral coordination of Al is observed that distinguishes technogenic steklite from that found in Tolbachik fumaroles. The (K,Na)3Na3(Fe,Al)2(SO4)6 phase is trigonal, space group R3¯, a = 13.932(2), c = 17.992(2) Å, V = 3024.4(7) Å3, R1 = 0.073 (wR2 = 0.108). The crystal structure is based upon the anionic chains [(Fe,Al)(SO4)3]3− running parallel to the c axis and interconnected via K+ and Na+ ions. There are no known minerals or synthetic compounds isotypic to (K,Na)3Na3(Fe,Al)2(SO4)6, due to the presence of separate K and Na sites in its structure.

Zn and Ni complexes of pyridine-2,6-di-carboxyl-ates: crystal field stabilization matters!

Six reaction products of ZnII and NiII with pyridine-2,6-di-carb-oxy-lic acid (H2Lig1), 4-chloro-pyridine-2,6-di-carb-oxy-lic acid (H2Lig2) and 4-hy-droxy-pyridine-2,6-di-carb-oxy-lic acid (H2Lig3) are used to pinpoint the structural consequences of crystal field stabilization by an incomplete d shell. The pseudo-octa-hedral ZnII coordination sphere in bis-(6-carb-oxy-picolinato)zinc(II) trihydrate, [Zn(C7H4NO4)2]·3H2O or [Zn(HLig1)2]·3H2O, (1), is significantly less regular than that about NiII in the isostructural compound bis-(6-carb-oxy-picolinato)nickel(II) trihydrate, [Ni(C7H4NO4)2]·3H2O or [Ni(HLig1)2]·3H2O, (2). The ZnII complexes poly[(4-chloro-pyridine-2,6-di-carboxyl-ato)zinc(II)], [Zn(C7H2ClNO4)] n or [Zn(Lig2)] n , (3), and poly[[(4-hy-droxy-pyridine-2,6-di-carboxyl-ato)zinc(II)] monohydrate], {[Zn(C7H3NO5)]·H2O} n or {[Zn(Lig3)]·H2O} n , (4), represent two-dimensional coordination polymers with chelating and bridging pyridine-2,6-di-carboxyl-ate ligands in which the coordination polyhedra about the central cations cannot be associated with any regular shape; their coordination environments range between trigonal-bipyramidal and square-pyramidal geometries. In contrast, the corresponding adducts of the diprotonated ligands to NiII, namely tri-aqua-(4-chloro-pyridine-2,6-di-carboxyl-ato)nickel(II), [Ni(C7H2ClNO4)(H2O)3] or [NiLig2(OH2)3)], (5), and tri-aqua-(4-hy-droxy-pyridine-2,6-di-carboxyl-ato)nickel(II) 1.7-hydrate, [Ni(C7H3NO5)(H2O)3]·1.7H2O or [NiLig3(OH2)3)]·1.7H2O, (6), feature rather regular octa-hedral coordination spheres about the transition-metal cations, thus precluding the formation of analogous extended structures.

A new one-dimensional CdII coordination polymer incorporating 2,2'-(1,2-phenylene)bis(1H-imidazole-4,5-dicarboxylate).

Imidazole-4,5-dicarboxylic acid (H3IDC) and its derivatives are widely used in the preparation of new coordination polymers owing to their versatile bridging coordination modes and potential hydrogen-bonding donors and acceptors. A new one-dimensional coordination polymer, namely catena-poly[[diaquacadmium(II)]-μ3-2,2'-(1,2-phenylene)bis(1H-imidazole-4,5-dicarboxylato)], [Cd(C16H6N4O8)0.5(H2O)2]n or [Cd(H2Phbidc)1/2(H2O)2]n, has been synthesized by the reaction of Cd(OAc)2·2H2O (OAc is acetate) with 2,2'-(1,2-phenylene)bis(1H-imidazole-4,5-dicarboxylic acid) (H6Phbidc) under solvothermal conditions. In the polymer, one type of Cd ion (Cd1) is six-coordinated by two N atoms and two O atoms from one H2Phbidc4- ligand and by two O atoms from two water molecules, forming a significantly distorted octahedral CdN2O4 coordination geometry. In contrast, the other type of Cd ion (Cd2) is six-coordinated by two N atoms and two O atoms from two symmetry-related H2Phbidc4- ligands and by two O atoms from two symmetry-related water molecules, leading to a more regular octahedral coordination geometry. The Cd1 and Cd2 ions are linked by H2Phbidc4- ligands into a one-dimensional chain which runs parallel to the b axis. In the crystal, the one-dimensional chains are connected through hydrogen bonds, generating a two-dimensional layered structure parallel to the ab plane. Adjacent layers are further linked by hydrogen bonds, forming a three-dimensional structure in the solid state.

Crystal structure of catena-poly[[[aqua-bis-(di-methyl-formamide-κO)magnesium(II)]-μ3-(2,2'-bi-pyridine-5,5'-di-carboxyl-ato-κ5O2:O2':N,N':O5)-[di-chlorido-platinum(II)]] di-methyl-formamide monosolvate

The title compound, {[MgPtCl2(C12H6N2O4)(C3H7NO)2(H2O)]·C3H7NO} n , is a one-dimensional coordination polymer. The structure consists of Pt-functionalized bi-pyridine ligands connected by MgII cations, as well as coordinating and non-coordinating solvent mol-ecules. The PtII cation is coordinated by the two N atoms of the bi-pyridine moiety and two Cl atoms in a square-planar fashion. This coordination induces an in-plane bend along the bi-pyridine backbone of approximately 10° from the linear ideal of a conjugated π-system. Likewise, the coordination to the MgII cation induces a significant bowing of the plane of the bi-pyridine of about 12°, giving it a distinct curved appearance. The carboxyl-ate groups of the bi-pyridine ligand exhibit moderate rotations relative to their parent pyridine rings. The MgII cation has a fairly regular octa-hedral coordination polyhedron, in which three vertices are occupied by O atoms from the carboxyl-ate groups of three different bi-pyridine ligands. The remaining three vertices are occupied by the O atoms of two di-methyl-formamide (DMF) mol-ecules and one water mol-ecule. The one-dimensional chains are oriented in the [01-1] direction, and non-coordinating DMF mol-ecules can be found in the space between the chains. The shortest inter-molecular O⋯H contacts are 2.844 (4) and 2.659 (4) Å, suggesting moderate hydrogen-bonding inter-actions. In addition, there is a short inter-molecular Pt⋯Pt contact of 3.491 (1) Å, indicating a Pt stacking inter-action. Some structure-directing contribution from the hydrogen bonding and Pt⋯Pt inter-action is probable. However, the crystal packing seems to be directed primarily by van der Waals inter-actions.

Crystal structure of new ammonium fluoroindate(III) (NH4)2[InF5

A new indium(III) fluoride complex with the ammonium cation (NH4)2[InF5] is synthesized and its crystal structure is studied. The structure of (NH4)2[InF5] is formed of NH4 + cations and complex [InF5]2– anions. The In atom in the complex anion surrounded by four terminal and two bridging F atoms forms an almost regular octahedral coordination polyhedron (CN 6) with two terminal F atoms in the axial positions and two terminal and two bridging F atoms in the equatorial plane. Through bridging F atoms, the InF6 polyhedra are arranged in polymer trans- vertex-connected corrugated anion chains (InF5) n 2n− directed along the c axis. The N–H⋯F hydrogen bonds organize the chains in a three-dimensional framework.

Chiral six-coordinate Dy(iii) and Tb(iii) complexes of an achiral ligand: structure, fluorescence, and magnetism.

Two new chiral six-coordinate lanthanide complexes (1 for Dy and 2 for Tb) have been synthesized using the achiral flexible ligand H2L (2,2'-[1,2-ethanediylbis[(methylimino)methylene]]bis[4,5-dimethylphenol]). Both complexes crystallize in the chiral P1 group space, and the enantiomers [Zn(L)Cl]3Dy·MeOH·0.5H2O (Λ-1), [Zn(L)Cl]3Dy·1.5H2O (Δ-1), [Zn(L)Cl]3Tb·1.5H2O (Λ-2) and [Zn(L)Cl]3Tb·H2O (Δ-2) are isolated in the reaction. Three [Zn(L)Cl]- anions coordinate to the central lanthanide ion using two phenoxo oxygen atoms of L2-, and the lanthanide ion has the coordination geometry of D3. Complex 1 exhibits a field-induced slow magnetization relaxation, which is typical of a single-ion magnet (SIM). Ab initio calculations on complex 1 and studies on magneto-structural correlationship of six-coordinate Dy(iii) SIMs indicate that the small energy barrier of complex 1 might be related to the absence of a unique anisotropic axis for the regular octahedral coordination configuration of Dy(iii) and the high quantum tunneling gap between the ground states (mJ = ±15/2). Complex 2 displays green photofluorescence and triboluminescence.

A review of the structural architecture of tellurium oxycompounds

AbstractRelative to its extremely low abundance in the Earth's crust, tellurium is the most mineralogically diverse chemical element, with over 160 mineral species known that contain essential Te, many of them with unique crystal structures. We review the crystal structures of 703 tellurium oxysalts for which good refinements exist, including 55 that are known to occur as minerals. The dataset is restricted to compounds where oxygen is the only ligand that is strongly bound to Te, but most of the Periodic Table is represented in the compounds that are reviewed. The dataset contains 375 structures that contain only Te4+cations and 302 with only Te6+, with 26 of the compounds containing Te in both valence states. Te6+was almost exclusively in rather regular octahedral coordination by oxygen ligands, with only two instances each of 4- and 5-coordination. Conversely, the lone-pair cation Te4+displayed irregular coordination, with a broad range of coordination numbers and bond distances. A threshold was applied for Te4+–O links of ∼2.45 Å or 0.3 valence units with some flexibility, as a criterion to define strongly bound Te–O polymers and larger structural units. Using this criterion, Te4+cations display one-sided 3-, 4- or 5-coordination by oxygen (with rare examples of coordination numbers 2 and 6). For both valence states of Te, examples are known of TemOncomplexes which are monomeric (m= 1; neso), noncyclic finite oligomers (soro), rings (cyclo), infinite chains (ino), layers (phyllo) and frameworks (tecto tellurates). There is a clear analogy to the polymerization classes that are known for silicate anions, but the behaviour of Te is much richer than that of Si for several reasons: (1) the existence of two cationic valence states for Te; (2) the occurrence of multiple coordination numbers; (3) the possibility of edge-sharing by TeOnpolyhedra; (4) the possibility for oxygen ligands to be 3-coordinated by Te; and (5) the occurrence of TemOnpolymers that are cationic, as well as neutral or anionic. While most compounds contain only one or two symmetrically distinct types of Te atom, Pauling's Fifth Rule is frequently violated, and stoichiometrically simple compounds such as CaTeO3can have polymorphs with up to 18 distinct Te sites. There is a tendency for local symmetry features such as the threefold axis of a TeO6octahedron or the acentric symmetry of a Te4+Onpolyhedron to be inherited by the host structure; the latter in particular can lead to useful physical properties such as nonlinear optical behaviour. We develop for the first time a hierarchical taxonomy of Te-oxysalt structures, based upon (1) valence state of Te; (2) polymerization state of TemOncomplexes; (3) polymerization state of larger strongly-bound structural units that include non-Te cations. Structures are readily located and compared within this classification.

The crystal structure of a new polymorph of hexa-aqua-nickel(II) bis-(6-oxo-1,6-di-hydro-pyridine-3-carboxyl-ate).

In a new polymorph of the title salt, [Ni(H2O)6](C6H4NO3)2, the metal atom of the cationic complex lies on a symmetry centre and is coordinated by six water mol­ecules to provide a quite regular octa­hedral coordination environment. These cations inter­act with 6-oxo-1,6-di­hydro­pyridine-3-carboxyl­ate anions through electrostatic inter­actions and by means of O—H⋯O and N—H⋯O hydrogen bonds involving the carboxyl­ate, keto and protonated imine groups of the anion, and the coordinating water mol­ecules from the cationic complex entity to generate a supra­molecular three-dimensional architecture. The previously reported polymorph of this compound presents a network of hydrogen bonds, in which the organic anions establish mutual hydrogen-bonding inter­actions involving their keto and protonated imine groups.

Hydroterskite: A New Mineral Species From the Saint-Amable Sill, Quebec, and A Comparison With Terskite and Elpidite

Hydroterskite, ideally Na 2 ZrSi 6 O 12 (OH) 6 , is a new mineral species from the Saint-Amable sill at the Demix-Varennes quarry, near Varennes, Quebec, Canada. Hydroterskite crystals are short prismatic in habit, up to 3 mm in width, and bounded by the {100}, {010}, and {001} prisms. The crystals are translucent, pale gray in color, with a white streak and vitreous luster. Hydroterskite is brittle and splintery, with good cleavages on the prismatic planes. It is biaxial negative, α = 1.562 ± 0.002, β = 1.567 ± 0.002, γ = 1.571 ± 0.002, 2 V meas. = 86(3)°, 2 V calc. = 83°. Dispersion could not be observed, and there is no pleochroism. The optical orientation is X = c , Y = b , and Z = a . The average result of three analyses of a single grain (oxide wt.%) gave Na 2 O 7.82, K 2 O 0.07, CaO 0.62, FeO 0.89, MnO 0.71, Al 2 O 3 0.08, La 2 O 3 0.12, Ce 2 O 3 0.24, SiO 2 59.82, HfO 2 0.11, ThO 2 1.15, ZrO 2 15.00, TiO 2 1.15, Nb 2 O 5 1.12, F 0.11, H 2 O (by stoichiometry) 8.79, for a total (−0.05 O=F) of 96.84. Magnesium, Y, Sr, and Cl were sought but not detected. The empirical formula on the basis of 18 anions with 6 OH − is (Na 1.543 K 0.009 Ca 0.068 La 0.005 Ce 0.009 ) ∑1.634 (Zr 0.744 Ti 0.088 Nb 0.052 Th 0.005 Hf 0.003 Fe 0.076 Mg 0.002 Mn 0.061 Al 0.010 ) ∑1.041 Si 6.087 O 12 (OH 5.963 F 0.035 Cl 0.002 ) ∑6 . The structure of hydroterskite is orthorhombic in the centric space group Pnca , with a 13.956(6), b 14.894(7), c 7.441(4) A, V 1546.8(2.0) A 3 , and Z = 4. It has been refined to an R index of 0.036 on the basis of 1080 observed reflections. There are two crystallographically distinct Na sites, both with eight-fold co-ordination: [ Na1 O 6 (OH) 2 ] is a hexagonal dipyramid polyhedron, whereas [ Na2 O 6 (OH) 2 ] is a bifurcated pentagonal dipyramid. The Zr atom is in a regular octahedral coordination. Silicon, in tetrahedral coordination with oxygen, forms spiral chains parallel to the c axis. These chains are cross-linked by edge-sharing [ZrO 6 ] octahedra and [NaO 8 ] polyhedra. All three H atoms were located. The crystal-structure determination of terskite in the literature was most likely incorrectly assigned to an acentric space-group. The hydroterskite crystal structure is compared to the structures of terskite, elpidite, and yusupovite.

MAMMOTHITE: A Pb-Sb-Cu-Al OXY-HYDROXIDE-SULFATE -- HYDROGEN ATOM DETERMINATION LOWERS SPACE GROUP SYMMETRY

Abstract The crystal structure of mammothite, Pb 6 Cu 4 AlSbO 2 (SO 4 ) 2 Cl 4 (OH) 16 , is monoclinic in acentric space group C 2, with a 18.959(4), b 7.3398(19), c 11.363(3) A, β 112.428(9)˚, V 1461.6(1.0) A 3 , and Z = 2. It has been refined to an R index of 0.019 on the basis of 3878 observed reflections. There are three crystallographically distinct Pb sites with two different co-ordinations: [Pb1O 8 Cl 1 ] is a mono-capped square antiprism polyhedron, while [Pb21O 7 Cl 2 ] and [Pb22O 7 Cl 2 ] are tri-capped trigonal prisms. Both Cu 2+ sites have distorted [4 + 2] octahedral coordination due to the Jahn-Teller effect. The Al and Sb sites are regular-octahedral co-ordination with oxygen atoms. The [SO 4 ] tetrahedron is quite distorted, with S–O bond lengths varying from 1.45 to 1.52 A and subtended O–S–O angles varying from 106 to 113˚. In the structure there are eight (OH) – anions. All eight H atoms pfu were located, and it is these structure sites that reduce the symmetry from centric to acentric. Although mammothite is classified as a framework structure, it has a distinct layering. There are two layer types in the mammothite structure that parallel (001). There are three octahedrally coordinated sites; two are occupied by Cu atoms and one by an Al atom, in the octahedral layer. The tetragonal dipyramids [CuO 6 ] are linked forming ‘olivine-like’ chains parallel to the b -axis. The second layer, termed the cross-linked layer, has three [PbO 9 ] polyhedra with shared edges forming chains parallel to the b -axis, like the [CuO 6 ] tetragonal dipyramids. These chains are cross-linked by edge-sharing [SbO 6 ] octahedra and decorated with [SO 4 ] groups. The H atoms are in ‘holes’ within both layers.

DFT Study of the Role of Al3+ in the Fast Ion-Conductor Li7-3x Al3+x La3Zr2O12 Garnet.

We investigate theoretically the site occupancy of Al3+ in the fast-ion-conducting cubic-garnet Li7–3xAl3+xLa3Zr2O12 (Ia-3d) using density functional theory. By comparing calculated and measured 27Al NMR chemical shifts an analysis shows that Al3+ prefers the tetrahedrally coordinated 24d site and a distorted 4-fold coordinated 96h site. The site energies for Al3+ ions, which are slightly displaced from the exact crystallographic sites (i.e., 24d and 96h), are similar leading to a distribution of slightly different local oxygen coordination environments. Thus, broad 27Al NMR resonances result reflecting the distribution of different isotropic chemical shifts and quadrupole coupling constants. From an energetic point of view, there is evidence that Al3+ could also occupy the 48g site with its almost regular octahedral coordination sphere. Although this has been reported by neutron powder diffraction, the NMR chemical shift calculated for such an Al3+ site has not been observed experimentally.

Catena-Poly[tris(μ3-acetylacetonato)nickelate(II)sodium(I)

The title complex, [NaNi(C5H7O2)3]n, contains an anionic tris(acetylacetonato)nickelate(II) unit, [Ni(acac)3](-) (acac is acetylacetonate), with a highly regular octahedral coordination geometry. The Ni(II) cation lies on a Wyckoff a site, resulting in D3 symmetry of the anion. Charge balance is provided by sodium cations, which occupy Wyckoff type b sites. Each sodium cation is surrounded by two [Ni(acac)3](-) anions, each of which is connected to the alkali metal through three O atoms, in a fac configuration. This arrangement leads to the formation of linear [Na{Ni(acac)3}]n chains along the c axis. The Ni···Na distance is 2.9211 (10) Å. The title complex is one of the few examples of heterometallic systems based on alkali and transition metal cations bridged by acetylacetonate ligands.

Quadratite, AgCdAsS3: Chemical composition, crystal structure, and OD character

A re-investigation of the crystal structure of quadratite, ideally AgCdAsS3, was undertaken using a single crystal from the type locality, Lengenbach, Binntal, Switzerland. The average of five electron microprobe analyses led to the empirical formula (Ag0.994Cd0.738Pb0.231Cu0.006Tl0.005Mn0.003Fe0.004Zn0.002 Cr0.001)Σ=1.984(As0.955Sb0.003)Σ=0.958S3.058. A single-crystal structure refinement (R1 = 4.84% for 558 observed reflections) shows that quadratite crystallizes in the space group P4322 and exhibits an atomic arrangement similar to that of the recently approved new mineral manganoquadratite, AgMnAsS3. Like manganoquadratite, quadratite adopts a galena-derivative framework, with metal atoms occupying all the available octahedral interstices, although only M1 and M2 cations, occupied mainly by Cd, adopt a fairly regular octahedral coordination; the M3 cation, occupied by Ag, is located outside the center cavity in a square-pyramidal coordination, whereas Pb at the split position M3′ coordinates six S atoms. Arsenic also adopts a 3 + 3 asymmetrical coordination, thus forming the AsS3 pyramidal groups that typically occur in sulfosalts.

K2[FeII 3(P2O7)2(H2O)2

The title compound, dipotassium diaqua­bis­(diphosphato)triferrate(II), K2[FeII 3(P2O7)2(H2O)2], was synthesized under solvothermal conditions. The crystal structure is isotypic with its Co analogue. In the structure, there are two crystallographically distinct Fe positions; one lies on an inversion center, the other on a general position. The first Fe2+ cation adopts a regular octa­hedral coordination with six O atoms, whereas the other is coordinated by five O atoms and a water mol­ecule. The [FeO6] octa­hedron shares its trans-edges with an adjacent [FeO5(H2O)] octahedron; in turn, the [FeO5(H2O)] octa­hedron shares skew-edges with a neighbouring [FeO6] octa­hedron and an [FeO5(H2O)] octa­hedron, resulting in a zigzag octa­hedral chain running along [001]. The zigzag chains are linked to each other by the P2O7 diphosphate groups, leading to a corrugated iron diphosphate layer, [Fe3(P2O7)2(H2O)2]2−, parallel to (100). The inter­layer space is occupied by K+ cations, which adopt an eight-coordination to seven O atoms and one water mol­ecule from a neighbouring iron diphosphate layer. Thus, the K+ ions not only compensate the negative charge of the layer but also link the layers into a network structure.

A phenomenological model for the structure–composition relationship of the high Tc cuprates based on simple chemical principles

A simple phenomenological model for the relationship between structure and composition of the high Tc cuprates is presented. The model is based on two simple crystal chemistry principles: unit cell doping and charge balance within unit cells. These principles are inspired by key experimental observations of how the materials accommodate large deviations from stoichiometry. Consistent explanations for significant HTSC properties can be explained without any additional assumptions while retaining valuable insight for geometric interpretation. Combining these two chemical principles with a review of Crystal Field Theory (CFT) or Ligand Field Theory (LFT), it becomes clear that the two oxidation states in the conduction planes (typically d8 and d9) belong to the most strongly divergent d-levels as a function of deformation from regular octahedral coordination. This observation offers a link to a range of coupling effects relating vibrations and spin waves through application of Hund’s rules. An indication of this model’s capacity to predict physical properties for HTSC is provided and will be elaborated in subsequent publications. Simple criteria for the relationship between structure and composition in HTSC systems may guide chemical syntheses within new material systems.

A 57Fe Mössbauer spectroscopic study of sogdianite: an example of a symmetric electric field gradient around Fe3+

Sogdianite, a double-ring silicate of composition $$ ( {\text{Zr}}_{0. 7 6} {\text{Ti}}_{0. 3 8}^{4 + } {\text{Fe}}_{0. 7 3}^{3 + } {\text{Al}}_{0.13} )_{\Upsigma = 2} \left( {\square_{ 1. 1 5} {\text{Na}}_{0. 8 5} } \right)_{\Upsigma = 2} {\text{K}}[{\text{Li}}_{ 3} {\text{Si}}_{ 1 2} {\text{O}}_{ 30} ] $$ from Dara-i-Pioz, Tadjikistan, was studied by the combined application of 57Fe Mossbauer spectroscopy and electronic structure calculations. The Mossbauer spectrum confirms published microprobe and X-ray single-crystal diffraction results that indicate that Fe3+ is located at the octahedral A-site and that no Fe2+ is present. Both the measured and calculated quadrupole splitting, ΔE Q, for Fe3+ are virtually 0 mm s−1. Such a value is unusually small for a silicate and it is the same as the ΔE Q value for Fe3+ in structurally related sugilite. This result is traced back to the nearly regular octahedral coordination geometry corresponding to a very symmetric electric field gradient around Fe3+. A crystal chemical interpretation for the regular octahedral geometry and the resulting low ΔE Q value for Fe3+ in the Mossbauer spectrum of sogdianite is that structural strain is largely “taken up” by weak Li–O bonds permitting highly distorted LiO4 tetrahedra. Weak Li–O bonding allows the edge-shared more strongly bonded Fe3+O6 octahedra to remain regular in geometry. This may be a typical property for all double-ring silicates with tetrahedrally coordinated Li.

Crystal structure of whiteite-(CaFeMg) from Crosscut Creek, Canada

The structural characterization of whiteite-(CaFeMg), a natural orthophosphate from Crosscut Creek, Yukon, Canada, with chemical composition (Ca0.86Na0.05)Σ = 0.91(Fe0.88Mn0.02)Σ = 0.90Mg2.17Al1.93(PO4)4(OH)2 · 8 H2O obtained by WDS-EMPA, was carried out by means of single crystal X-ray diffraction. The structure was solved in the P2/a monoclinic space group, with the following unit cell constants: a = 14.8700(15), b = 6.9785(5), c = 9.9268(10) Å, β = 110.110(1)°, V = 967.31(15) Å3. Structure refinement lead to the crystal chemical formula (Ca0.95Na0.11)Σ = 1.06Fe0.90Mg2.01Al2.05 (PO4)4(OH)1.99 · 8.17 H2O. Phosphorus atoms display tetrahedral (PO4) coordination, while magnesium, iron(II) and aluminum display regular octahedral coordination; calcium displays a complex CaO8 coordination. MgO2(H2O)4, FeO6, AlO4(OH)2, CaO8 polyhedra and PO4 groups are arranged such as to form a three-dimensional framework via edge- and vertex-sharing arrangements. Strong O—H … O hydrogen bonds contribute to stabilize the array: such interactions were also investigated by means of Libowitzky formula (Libowitzky, 1999) application, owing to the results of IR spectroscopy.