Bond Valence Sum Calculations Research Articles

A series of [NaMnIII3MnII] clusters constructed using a multidentate Schiff-base ligand and decorated with different auxiliary ligands

Four new polynuclear clusters [NaMnIII3MnII(HL)3(μ4-O)(μ1,1-N3)3]ClO4·CH3CH2OH·(H2O)3 (1), [NaMnIII3MnII(HL)3(μ4-O)(μ1,1-N3)2(μ1,3-N3)]ClO4·CH3CH2OH·H2O (2), [NaMnIII3MnII(HL)3(μ4-O)(HCOO)3]ClO4·(H2O)4 (3) and [NaMnIII3MnII(HL)3(μ4-O)(PhCOO)(H2O)2](ClO4)2·H2O·PhCOO·PhCOOH·CH3OH (4) have been obtained via self-assembly between 3-((2-hydroxy-3-methoxybenzylidene)amino)propane-1,2-diol (H3L: condensed from o-vanillin and 3-amino-1,2-propanediol) and the auxiliary bridges (N3−, HCOO−, PhCOO−, H2O) with Mn(ClO4)2·6H2O in the air-exposed methanol solution. The structures of 1–4 all contain [NaMnIII3MnII] units and show a very similar trigonal propeller-like shape. The valences of the metal ions were determined by detection of the Jahn–Teller distortion visible for MnII,III, and confirmed by bond-valence sum (BVS) calculations. Three MnIII ions and one MnII ion take the shape of a super-tetrahedron with the MnII ion lying above the triangular [Mn3O] plane constructed from three MnIII ions linked by a central μ4-O atom. The NaI ion which lies below the [Mn3O] plane is linked with MnIII ions through the oxygen atoms from Schiff base ligands. The main structural difference in the four clusters is caused by the different bridging modes among MnIII ions. A structural comparison of 1–4 demonstrates that the auxiliary ligands play a key role in governing the coordination motifs. Moreover, the magnetic properties of these clusters exhibit dominating antiferromagnetic exchange interaction between spin carriers of MnII,III.

X-ray Crystal Structure Analysis and Ru Valence of Ba4Ru3O10Single Crystals

We present the single-crystalline x-ray diffraction study on the Ba4Ru3O10 consisting of the corner-shared Ru3O12 trimers. The crystal structure is re-determined from 78 to 300 K across an antiferromagnetic transition at 105 K. The orthorhombic symmetry (Cmca, space group No. 64) is preserved at all temperatures measured. This structure presents exceptionally long Ru-O distances characterized by a significant distribution within the Ru3O12 trimer. A bond valence sum calculation suggests that the charge disproportionation within the Ru3O12 trimer emerges even at room temperature, which we ascribe to molecular orbital formation in the Ru3O12 trimer, as supported by recent theoretical calculations. Based on the analyzed crystal structure, the electronic states and the nature of the phase transition at 105 K are discussed.

Dinuclear CuII–CuII and CuI–CuII Complexes of a Compartmental Ligand – Syntheses, Structures, Magnetic, and Catalytic Studies

AbstractDinuclear CuII–CuII (1) and CuI–CuII (2) complexes were derived from a new N4O2 donor compartmental ligand (H2L) by changing the nature of the Cu precursors used. Single‐crystal X‐ray diffraction studies revealed that the Cu1 site in 1 has octahedral geometry and is in the inner compartment of the ligand axially coordinated by two ClO4– anions, whereas the outer Cu2 ion has square‐pyramidal geometry. In 2, there are two copper dinuclear complexes (A and B) in the asymmetric unit; the inner core is occupied by Cu1/Cu3 in the +2 oxidation state in a square‐planar geometry. The Cu2/Cu4 ion occupies the outer sites and has distorted tetrahedral geometry with a +1 oxidation state. Complexes 1 and 2 were obtained simply by changing Cu(ClO4)2 in 1 to Cu(ClO4)2 and Cu(bipy)(NO3)2 in 2; the bipyridyl (bipy) ligand induces the reduction of CuII to CuI, which is trapped in the CuI–CuII dinuclear product. The oxidation states of the metal ions were ascertained from charge‐balance considerations as well as from bond valence sum (BVS) calculations. No signature of intervalence charge transfer (IVCT) was observed by spectroscopy (UV/Vis/NIR) as well as from the low‐temperature magnetic studies. This might be because of the presence of two copper centers in two different geometries with a wide separation between them (ca. 3.27 Å). For 1, the best fit of the χT vs. T data to the dimer model gives J/kB = –262(1) K and gav = 2.05(5), which indicates that there is a strong antiferromagnetic coupling between the two Cu atoms. In 2, the CuI center is diamagnetic and, thus, the remaining S = 1/2 CuII magnetic center follows a Curie law with g = 2.06(5). Under homogeneous conditions, both complexes showed catalytic epoxidation of cyclooctene, styrene, and norbornene to the corresponding epoxides with high selectivities and turnover numbers (TONs), which seem to be slightly better than the reported values for CuII Schiff base complexes.

Homo- and Heterometal Complexes of Oxido–Metal Ions with a Triangular [V(V)O–MO–V(V)O] [M = V(IV) and Re(V)] Core: Reporting Mixed-Oxidation Oxido–Vanadium(V/IV/V) Compounds with Valence Trapped Structures

A new family of trinuclear homo- and heterometal complexes with a triangular [V(V)O-MO-V(V)O] (M = V(IV), 1 and 2; Re(V), 3] all-oxido-metal core have been synthesized following a single-pot protocol using compartmental Schiff-base ligands, N,N'-bis(3-hydroxysalicylidene)-diiminoalkanes/arene (H4L(1)-H4L(3)). The upper compartment of these ligands with N2O2 donor combination (Salen-type) contains either a V(IV) or a Re(V) center, while the lower compartment with O4 donor set accommodates two V(V) centers, stabilized by a terminal and a couple of bridging methoxido ligands. The compounds have been characterized by single-crystal X-ray diffraction analyses, which reveal octahedral geometry for all three metal centers in 1-3. Compound 1 crystallizes in a monoclinic space group P2(1)/c, while both 2 and 3 have more symmetric structures with orthorhombic space group Pnma that renders the vanadium(V) centers in these compounds exactly identical. In DMF solution, compound 1 displays an 8-line EPR at room temperature with <g> and <A> values of 1.972 and 86.61 × 10(-4) cm(-1), respectively. High-resolution X-ray photoelectron spectrum (XPS) of this compound shows a couple of bands at 515.14 and 522.14 eV due to vanadium 2p(3/2) and 2p(1/2) electrons in the oxidation states +5 and +4, respectively. All of these, together with bond valence sum (BVS) calculation, confirm the trapped-valence nature of mixed-oxidation in compounds 1 and 2. Electrochemically, compound 1 undergoes two one-electron oxidations at E(1/2) = 0.52 and 0.83 V vs Ag/AgCl reference. While the former is due to a metal-based V(IV/V) oxidation, the latter one at higher potential is most likely due to a ligand-based process involving one of the catecholate centers. A larger cavity size in the upper compartment of the ligand H4L(3) is spacious enough to accommodate Re(V) with larger size to generate a rare type of all-oxido heterotrimetallic compound (3) as established by X-ray crystallography.

Structural and Mössbauer study of the Brownmillerite oxides LaSrMn2−xFexO5 (0 ⩽ x ⩽ 0.5)

Iron doped brownmillerite oxides LaSrMn2−xFexO5 (0⩽x⩽0.5) have been prepared as pure powders by a conventional solid state reaction and studied by X-ray powder diffraction, scanning electronic microscope and Mössbauer spectroscopy. Rietveld analysis of X-ray diffraction patterns confirms that all samples crystallize in the orthorhombic system with Pnma space group and are isotypic with the Ca2Fe1.039Mn0.962O5 phase. Cell parameters and crystallite size show an anomaly around x=0.2 which is explained by the partial substitutions of Mn2+ and Mn3+ by Fe3+ and small amounts of Fe4+. A detailed analysis of the Mössbauer spectra for all compounds measured at room temperature shows that Fe3+ ions are located in distorted octahedral and tetrahedral sites. The environment and oxidation states of Mn and Fe are determined by bond valence sum calculations and the results for Fe are compared to the results from the Mössbauer study.

Structure of New Layered Bimetallic Hydrogenoselenite Copper Selenium

The structure of a newly layered copper selenium hydrogenoselenite [Cu(HSeO3)2Cu0.335Se0.582Cl3(H2O)3] has been solved from single crystal X-ray diffraction data and refined to a final reliability factor R 1 = 0.038. It was found having an orthorhombic space group Pna21, with a = 9.0743(4) A, b = 7.1753(4) A, c = 17.7246(9) A, V = 1154.06(10) A3, and Z = 4. This structure is three-dimensional but it may be described as a bi-dimensional structure made of layers, parallel to the (010) plane, which contain copper atoms and (HSeO3)− anions. The sheets are interconnected by [CuCl3(H2O)3] groups. The Se and Cu oxidation state was evaluated using bond valence sum calculations. The presence of hydrogenoselenites (νSe–O–H, 1,222 cm−1) was confirmed by IR and Raman spectra. The dielectric constant at different frequencies and temperatures revealed a phase transition at 383 K.

Topochemical modifications of mixed metal oxide compounds by low-temperature fluorination routes

AbstractIn this review, we discuss recent developments in the use of low-temperature fluorination routes for the topochemical modification of mixed metal oxide compounds. By applying such methods, material properties (such as magnetism, superconductivity, electrical conductivity, and ionic conductivity) can be tuned in a wide range. Furthermore, oxide fluoride compounds are interesting from a structural point of view, and while differentiating between oxide and fluoride ions has proved to be difficult using diffraction methods, strategies (e.g., bond valence sum calculations) to overcome this problem have been shown to be possible. In addition, this review concludes with an outlook on future prospects in the field of oxide fluoride compounds.

A palladium(II) complex: Synthesis, structure, characterization, electrochemical behavior, thermal aspects, BVS calculation and antimicrobial activity

The reaction of equimolar proportions of Na2[PdCl4] and 1-(4-methylimidazol-5-yl) phenylhydrazonopropane-2-one oxime (LH), a 1:1 Schiff-base condensate of 1-hydrazono-1-phenyl-propan-2-one oxime (1) and 4-methylimidazole-5-carboxaldehyde, in methanol gives rise to [Pd(L)(Cl)] (2) in a satisfactory yield. The title monomeric palladium(II) complex, 2, has been characterized by C, H and N microanalyses, 1H and 13C NMR, FAB-MS, FT-IR, UV–Vis spectra, molar electric conductivity measurements and room temperature magnetic susceptibility measurements. The X-ray crystal structures of 1 and 2 have been determined. The structure of 1, a precursor of the ligand (LH), shows that the methyl and phenyl groups are in an ‘anti’ disposition. Compound 1 crystallizes in the monoclinic space group P21 with a=6.9503(5), b=6.4535(3), c=10.1631(6)Å, V=455.04(5)Å3 and Z=2. The structure of 2 reveals that it is a distorted square-planar palladium(II) compound. The palladium center is in an ‘N3Cl’ coordination chromophore. Complex 2 crystallizes in the tetragonal space group I41/a with a=22.5744(3), b=22.5744(3), c=13.2967(2)Å, V=6776.05(16)Å3 and Z=16. The thermal and electrochemical aspects of 2 have been studied. Electrochemical studies in DMF show a Pd(II) to Pd(III) oxidation at 0.573V, along with a reduction of Pd(II) to Pd(I) at −0.757V versus Ag/AgCl. A Bond-Valence Sum (BVS) model calculation was performed to assign the oxidation state of the palladium center in 2. The in vitro antimicrobial activity of 2 was tested against both Gram positive and Gram negative bacteria. Complex 2 exhibits satisfactory bacteriostatic activity.

Oligonuclear homo- and mixed-valence manganese complexes based on thiophene- or aryl-carboxylate ligation: Synthesis, characterization and magnetic studies

Mixed-valence trinuclear manganese compounds [Mn3O(O2CTh)6(L)x(H2O)y]·n(solvent) (Th=thiophene, 1·CH3CN: L=pyridine (py), x=3, y=0, n=1, solvent=CH3CN; 1·∼H2O: L=py, x=3, y=0, n=∼1, solvent=H2O; 2: L=py, x=2, y=1, n=0.25, solvent=CH3CN; 3: L=3-Mepy, x=2, y=1, n=0) containing a [MnIIMn2III(μ3-O)]6+ core have been prepared. Homo-valence tetranuclear manganese complexes (NBun4)[Mn4O2(O2CAr)9(L)] (4·ThCO2H·CH2Cl2: Ar=–Th, L=EtOH; 6: Ar=–Ph, L=H2O; 7: Ar=–Ph-p-Me, L=H2O; 8·CH2Cl2: –Ph-3,5-Me2, no L) with a [MnIII4(μ3-O)2]8+ core and [MnIIMnIII3O2(O2CTh)7(bpy)2] (5) were synthesized, structurally and magnetically characterized. Compounds 1–3 were obtained by comproportionation of MnII(O2CMe)2·4H2O with (NBun4)MnVIIO4 in aprotic pyridine (1) or aprotic/protic py/EtOH (2) or Mepy/EtOH (3) solvent mixtures. Clusters 4–8 were synthesized by comproportionation of MnII(O2CAr)2·xH2O/ArCOOH with (NBun4)MnVIIO4 in EtOH/CH3CN. X-ray structural characterization of the 2-thiophenecarboxylate (ThCO2−) containing compounds 1·CH3CN, 1·∼2H2O and 4·ThCO2H·CH2Cl2 revealed a thiophene ring disorder about the (O2)C–C(Th) bond so that the S atom and opposite (5–)CH group are distributed over two ring positions each. The MnII atom in the approximately isosceles triangular [MnIIMn2III(μ3-O)]6+ cores in 1 could be clearly assigned from bond valence sum calculations and bond distances. The [Mn4(μ3-O)2]8+ core in the anionic complexes in the structures of 4·ThCO2H·CH2Cl2 and 8·CH2Cl2 has an all MnIII oxidation level and “butterfly-like” arrangement. The magnetic properties of 4–8 were investigated by variable temperature magnetic susceptibility and magnetization measurements. Similar magnetic behavior was observed for the [MnIII4(μ3-O)2]8+ butterfly-core compounds 4, 6–8, with antiferromagnetic interactions between pairs of manganese ions with amplitude of ∼14.5cm−1 and ∼4.6cm−1 for the Mnb⋯Mnb and Mnb⋯Mnw coupling, respectively (b=body, w=wing). Changing the Ar-ligand size in [Mn4O2(O2CAr)9(L)]− does not have a significant effect on the magnetic properties of these butterfly clusters.

Chessboard/Diamond Nanostructures and the A-site Deficient, Li1/2–3x Nd1/2+xTiO3, Defect Perovskite Solid Solution

The crystal chemical origin of nanoscale chessboard/diamond ordering in perovskite-related solid solutions of composition Li0.5–3xNd0.5+xTiO3 (LNT, x ∼ 0.02–0.12) is investigated. Experimental and simulated scanning transmission electron microscopy (STEM) images are found to be consistent with the compositional modulation model proposed by previous authors. However, these earlier models do not satisfactorily explain other features observed in high-resolution STEM and TEM images, such as the two-dimensional {100} lattice fringes with the same periodicity, √2ap × √2ap, as the local LNT unit cell viewed along the [001] direction (where ap is the parent perovskite unit cell parameter). Based on bond valence sum calculations, we propose a new set of crystal structures for LNT in which Li ions are primarily bonded to only two O ions, and order one-dimensionally with √2ap periodicity. Bright-field STEM image simulations performed for this new model reproduced the experimentally observed √2ap lattice fringes, thus strongly suggesting that the finer features of the high-resolution (S)TEM images are the result of Li ion ordering and associated local structural relaxation. In this new model, the LNT chessboard supercell then results from the ordered combinations of two sublattices: the Li ion sublattice and its translational variants on the one hand, and the Nd0.5TiO3 sublattice and its oxygen octahedral tilt twin variants on the other. Dielectric measurements indicate the presence of long-lived polar clusters that are easily activated under an applied electric field. This suggests that these clusters consist of spatially correlated Li ions.

Synthesis, spectroscopic, and crystallographic characterizations of an antiferromagnetically coupled, oxobridged trinuclear manganese(IV) cluster [Mn3O4(H2O)2(phen)4](NO3)4 · 3H2O [phen = 1,10-phenanthroline

Design and synthesis of a triangular manganese compound, [Mn3O4(H2O)2(phen)4](NO3)4 · 3H2O (1) with mono-µ-oxo and di-µ-oxo, is described. The complex has been characterized by elemental analysis, spectroscopy, single crystal and powder diffraction measurements, thermogravimetric analysis, etc. Bond Valence Sum calculations and X-ray photoelectron spectroscopy reveal that each manganese at each vertex of the triangle is +IV oxidation state. Variable temperature magnetic measurements show strong antiferromagnetic coupling between metal ions with the following set of parameters: g = 1.99, J 1 = −50.0 cm−1, and J 2 = −90.2 cm−1 (where J 1 describes the interaction across the two mono-µ-oxo bridges and J 2 is the exchange coupling across the di-µ-oxo bridge). The compound breaks down in three steps when heated from room temperature to 900°C. The final ash of the compound is confirmed by infrared spectrum with standard MnO2.

V16O38(CN)]9–: A Soluble Mixed-Valence Redox-Active Building Block with Strong Antiferromagnetic Coupling

A new discrete [V(16)O(38)(CN)](9-) cluster, which displays the hitherto unknown 8- charge on the cluster shell and is the first to encapsulate the cyanide anion, has been synthesized and characterized by IR and UV/vis/near-IR spectroscopy, electrochemistry, and magnetic susceptibility measurements. Bond valence sum calculations conducted on the basis of the crystal structure analysis of K(9)[V(16)O(38)(CN)]·13H(2)O confirm that this new member of the polyoxovanadate series is a mixed-valence complex. The intervalence charge transfer bands arising from intrametal interactions reveal that a localized (class II) assignment is appropriate for the cluster; however, a small degree of electronic delocalization is present. Interesting possibilities exist for the incorporation of this unit into higher dimensionality framework structures, where the redox, optical, and magnetic properties can be exploited and tuned.

Ferroelectric and octahedral tilt twin disorder and the lead-free piezoelectric, sodium potassium niobate system

Using electron diffraction, trends in the local structural behaviour of the KxNa1−xNbO3 (KNN x) ‘solid solution’ system are investigated and interpreted using an order/disorder based theoretical framework. At room temperature, electron diffraction shows a single plane of transverse polarised, diffuse intensity perpendicular to [010]p⁎ (p for parent sub-structure) across the entire phase diagram, indicative of ferroelectric disorder along the [010]p direction co-existing with long range ferroelectric order along the orthogonal [100]p and [001]p directions. An additional characteristic pattern of diffuse scattering is also observed, involving rods of diffuse intensity running along the [100]p* and [001]p* directions of the perovskite sub-structure and indicative of octahedral tilt disorder about the [100]p and [001]p axes co-existing with long range ordered octahedral tilting around the [010]p direction. A possible crystal chemical explanation for the existence of this latter octahedral tilt disorder is explored through bond valence sum calculations. The possible influence of both types of disorder on the previously refined, room temperature space group/s and average crystal structure/s is examined.

Room temperature relaxor ferroelectricity and spin glass behavior in Sr2FeTiO6 double perovskite

The structure, dielectric and magnetic properties of complex Sr2FeTiO6 double perovskite have been investigated. Reitveld analysis of X-ray powder diffraction pattern reveals that the material is stabilized in a cubic perovskite phase with Pm3¯m space group without the B-site cations ordering. The temperature evolution of crystal structural studies indicates the absence of structural changes with temperature. The scanning electron micrograph exhibits heterogeneous grain distribution with average grain size of 1–7.5μm. The bond valence sum calculations and diffusion-assisted small-polaron hopping conduction mechanism confirm the mixed valence state of Fe/Ti ions. Dielectric spectra show a broad dielectric anomaly coupled with a shift in dielectric maxima towards higher temperature with frequency, exhibiting a typical relaxor ferroelectric behavior. The relaxor behavior has been quantitatively characterized based on the phenomenological parameters (Tm, TB, γ, ΔTrelax). The agreement of dielectric relaxation with non-linear Vogel Fulcher relation indicates that the system is indeed a relaxor exhibiting glassy characteristics. The transport studies show a semiconductor like behavior and a negligible magnetoresistance. Furthermore, the magnetic characterisation exhibits a non-metallic spin-glass-like state below 16K, driven by competing interactions between the antiferromagnetic and the ferromagnetic states.

Incommensurate Modulated Structures in the Ta2O5 - Al2O3 System

Members of the (1 – x)Ta2O5·xAl2O3 series were synthesized, and the structures investigated using synchrotron X-ray powder diffraction and neutron powder diffraction data for the first time. Structural models were developed and refined using the Rietveld method and a [3 + 1] dimensional incommensurately modulated composite structure approach with a composition dependent modulation vector q, and superspace group Xmmm(0β0)s00. Displacive atomic modulation functions across the (1 – x)Ta2O5·xAl2O3 series were found to be very similar, and strongly resemble those for the Ta2O5–WO3 system, in line with the notion that there are structure types in higher dimensional space just as there are in 3D space. Bond valence sum calculations and bond distance plots showed that the introduction of the modulation to the structural model generally led to more favourable bond valence sum values and bond distances. Fourier difference plots were examined, and the occupational modulation of aluminium refined to determine that the aluminium atoms preferentially occupy the octahedral sites.

Reduction of Sterically Hindered β-Diketiminato Europium(iii) Complexes by the β-Diketiminato Anion: A Convenient Route for the Synthesis of β-Diketiminato Europium(ii) Complexes

The metathesis reaction of anhydrous EuCl(3) with sodium salt of bulky β-diketiminato NaL (L = [N(2, 4, 6- Me(3)C(6)H(2))C(Me)](2)CH(-), L(2, 4, 6-Me3); [N(2,6-(i)Pr(2)C(6)H(3))C(Me)](2)CH(-), L(2, 6-ipr2) and [(2, 6-(i)Pr(2)C(6)H(3))NC(Me)CHC(Me)N(C(6)H(5))](-), L(2, 6-ipr2)(Ph)) in THF at 60 °C afforded the corresponding Eu(II) complexes: Eu(II)(L(2, 4, 6-Me3))(2)(THF) (1), Eu(II)(L(2, 6-ipr2))(2) (2) and Eu(II)(L(2, 6-ipr2)(Ph))(2) (5) with the formations of dimers (L(2, 4, 6-Me3))(2) (3) and (L(2, 6-ipr2))(2) (4) for the former two reactions and proligand L(2, 6-ipr2)(Ph)H (6) for the latter one. Compounds 1-6 were confirmed by an X-ray crystal structure analysis. The central metal Eu(II) in 1 is coordinated by two monoanionic L(2, 4, 6-Me3) ligands and one THF molecule in a trigonal bipyramid. The Eu(II) in each of 2 and 5 is ligated by two monoanionic ligands to form a tetrahedral geometry. The BVS (Bond Valence Sum) calculation indicates the oxidation state of Eu in all the three complexes is 2+ (2.12 for 1, 1.86 for 2 and 1.99 for 5). The isolation of dimers of (L(2, 4, 6-Me3))(2) and L(2, 6-ipr2))(2) and proligand L(2, 6-ipr2)(Ph)H demonstrates that the reducing agent in the present reduction of a Eu(III) ion to a Eu(II) ion might be the (L(2, 4, 6-Me3))(-), (L(2, 6-ipr2))(-) and (L(2, 6-ipr2)(Ph))(-), respectively. The possible mechanism for the reduction pathway is presented.

Intriguing Interconnections Among Phase Transition, Magnetic Moment, and Valence Disproportionation in 2H-Perovskite Related Oxides

In this paper we report the crystal growth, structure determination, and magnetic properties of the 2H-perovskite related oxides, Sr(5)Co(4)O(12) and Sr(6)Co(5)O(15), as well as the charge disproportionation and associated phase transition of Sr(5)Co(4)O(12). Sr(5)Co(4)O(12) and Sr(6)Co(5)O(15) are the (m = 2, n = 3) and (m = 1, n = 1) members of the A(3m+3n)A'(n)B(3m+n)O(9m+6n) family, respectively. Sr(6)Co(5)O(15) crystallizes in the space group R32 with lattice parameters of a = 9.5020(10) Å and c = 12.379(8) Å. The structure solution shows that Sr(6)Co(5)O(15) is isostructural with Sr(6)Rh(5)O(15). Magnetic measurements do not indicate any long-range magnetic order, although the Weiss temperature of -248 K indicates the presence of dominant antiferromagnetic interactions. Sr(5)Co(4)O(12) crystallizes in the space group P-3c1 with lattice parameters of a = 9.4705(10) Å and c = 20.063(5) Å at room temperature. The single crystal structure solution revealed that the cobalt ions in the trigonal prismatic sites of Sr(5)Co(4)O(12) undergo a structural transition at ~170 K, where the cobalt atoms are in the center of the trigonal prisms below this temperature and move partially toward the faces above this temperature. This structure transition is accompanied by a change in the magnetic moment of the oxide and can be related to a valence disproportionation of the cobalt ions and a concomitant Jahn-Teller distortion. In addition, specific heat, Seebeck coefficient, electric conductivity, and magnetic measurements as well as bond valence sum calculations were carried out for Sr(5)Co(4)O(12). Sr(5)Co(4)O(12) exhibits strong magnetic anisotropy but no long-range magnetic order.

Can Hydrophobic Interactions Influence Supramolecular Aggregation in Self‐Assembled Organic–Inorganic Hybrid Structures?

AbstractThis study aims to provide insights into the ability of amphiphilic cations to influence the assembly of hybrid organic‐inorganic crystal lattices using hydrophobic interactions. To investigate the hypothesis, a prototype amphiphilic cation, tert‐butyldiethanolammonium, was employed together with molybdenum oxide clusters of increasing size and charge in the self‐assembly of type I hybrid systems. The molybdate clusters were used as model inorganic building blocks as they can be formed in situ and their size and charge can be adjusted by pH control. Using this strategy, three hybrid structures were obtained and characterized using single‐crystal X‐ray diffraction, theoretical bond valence sum calculations, elemental analysis, FTIR spectroscopy, thermogravimetry and theoretical Hirshfeld analysis. Heptamolybdate Na5[tBuNH(C2H4OH)2][Mo7O24]·ca. 14H2O (1) was isolated, which features sodium‐linked dimeric cluster species. Inaddition, octamolybdate [tBuNH(C2H4OH)2]4[Mo8O26]·ca. 4H2O (2) was isolated, which incorporates a complex cationic sodium network that contains isolated octadecanuclear sodium clusters. At low pH levels (below pH 2),[tBuNH(C2H4OH)2]14[Mo36O112(H2O)16][Mo36O112(H2O)14{tBuNH(C2H4OH)2}2]·ca. 36H2O (3) was obtained, which is based on a 36‐centre molybdenum oxide cluster. Crystallographic analysis of the assemblies showed that the formation of hydrophobic regions within the crystal lattice is affected by the size of the inorganic building blocks employed. In 1 and 2, the hydrophobic tert‐butyl groups of the amphiphilic cations aggregate into hydrophobic assemblies. In contrast, the structural arrangement in 3 is dominated by the large inorganic cluster and the organic cations are incorporated as isolated units. This behaviour is further supported by theoretical Hirshfeld surface analysis of the organic counterions, which suggests that, with increasing cluster size, the contribution of long‐range, hydrophobic intermolecular interactions decreases, which is in line with the crystallographic analysis for 1–3.

Structural evolution of one-dimensional spin-ladder compounds Sr14−xCaxCu24O41with Ca doping and related evidence of hole redistribution

Incommensurate crystal structures of spin ladder series Sr14-xCaxCu24O41 (x=3, 7, 11, 12.2) were characterized by powder neutron scattering method and refined using the superspace group Xmmm(00{\gamma})ss0 (equivalent to superspace group Fmmm(0,0,1+{\gamma})ss0); X stands for non-standard centering (0,0,0,0), (0,1/2,1/2,1/2), (1/2,1/2,0,0), (1/2,0,1/2,1/2)) with a modulated structure model. The Ca doping effects on the lattice parameters, atomic displacement, Cu-O distances, Cu-O bond angles and Cu bond valence sum were characterized. The refined results show that the CuO4 planar units in both chain and ladder sublattices become closer to square shape with an increase of Ca doping. The Cu bond valence sum calculation provided new evidence for the charge transfer from the chains to ladders (approximately 0.16 holes per Cu from x=0 to 12.2). The charge transfer was attributed to two different mechanisms: (a) the Cu-O bond distance shrinkage on the ladder; (b) increase of the interaction between two sublattices, resulting in Cu-O bonding between the chains and ladders. The low temperature structural refinement resulted in the similar conclusion, with a slight charge backflow to the chains.

Structure of LaTi2Al9O19 and reanalysis of the crystal structure of La3Ti5Al15O37

The non-perovskite compound LaTi(2)Al(9)O(19) was synthesized and structurally characterized by conventional X-ray powder diffraction and shown to be isostructural with SrTi(3)Al(8)O(19), as confirmed by bond-valence sum calculations. The dielectric properties of LaTi(2)Al(9)O(19) at 1 MHz were measured. The crystal structure of La(3)Ti(5)Al(15)O(37), which is referred to as the most complex structure solved ab initio from X-ray powder diffraction (XRPD) to date, is shown to be incorrect.