Montmorillonite and Beidellite Intercalated with Tetramethylammonium Cations

Molecular mechanics simulations, combined with X-ray powder diffraction and infrared spectroscopy, have been used in structure analysis of montmorillonite and beidellite intercalated with tetramethylammonium cations. A complex structure analysis provided us with the detailed structure model, including characterization of the disorder, the total sublimation energy and a charge distribution in the structure of intercalates. The calculated basal spacings (14.36 Å for TMA-montmorillonite and 14.12 Å for TMA-beidellite) are in good agreement with the experimental values (14.31 Å for TMA-montmorillonite and 14.147 Å for TMA-beidellite). Both intercalated structures exhibit positional and orientational disorder in the arrangement of TMA cations, and consequently disorder in layer-stacking. In the present work we analyse the effect of octahedral and tetrahedral substitutions in a 2:1 silicate layer on the arrangement of tetramethylammonium (TMA) cations in the interlayer space of montmorillonite and beidellite. The most significant difference between TMA-montmorillonite and TMA-beidellite is in the charge distribution on the TMA cations and silicate layer. The TMA-beidellite structure is highly polarized, the total charge on one TMA cation is +0.167 e^–, while the total charge on the TMA cation in montmorillonite is +0.050 e^–.     

Permeation and inhibition of polycystin-l channel by monovalent organic cations

Polycystin-L (PCL), homologous to polycystin-2 (71% similarity in protein sequence), is the third member of the polycystin family of proteins. Polycystin-1 and -2 are mutated in autosomal dominant polycystic kidney disease, but the physiological role of PCL has not been determined. PCL acts as a Ca-regulated non-selective cation channel permeable to mono- and divalent cations. To further understand the biophysical and pharmacological properties of PCL, we examined a series of organic cations for permeation and inhibition, using single-channel patch clamp and whole-cell two-microelectrode voltage clamp techniques in conjunction with Xenopus oocyte expression. We found that PCL is permeable to organic amines, methlyamine (MA, 3.8 Å), dimethylamine (DMA, 4.6 Å) and triethylamine (TriEA, 6 Å), and to tetra-alkylammonium cation (TAA) tetra-methylammonium (TMA, 5.5-6.4 Å). TAA compounds tetra-ethylammonium (TEA, 6.1-8.2 Å) and tetra-propylammonium (TPA, 9.8 Å) were impermeable through PCL and exhibited weak inhibition on PCL (IC₅₀ values>13 mM). Larger TAA cations tetra-butylammonium (TBA, 11.6 Å) and tetra-pentylammonium (TPeA, 13.2 Å) were impermeable through PCL as well and showed strong inhibition (IC₅₀ values of 2.7 mM and 1.3 μM, respectively). Inhibition by TBA was on decreasing the single-channel current amplitude and exhibited no effect on open probability (NP_o) or mean open time (MOT), suggesting that it blocks the PCL permeation pathway. In contract, TEA, TPA and TPeA reduced NP_o and MOT values but had no effect on the amplitude, suggesting their binding to a different site in PCL, which affects the channel gating. Taken together, our studies revealed that PCL is permeable to organic amines and TAA cation TMA, and that inhibition of PCL by large TAA cations exhibits two different mechanisms, presumably through binding either to the pore pathway to reduce permeant flux or to another site to regulate the channel gating. These data allow to estimate a channel pore size of ∼7 Å for PCL.     

Adsorption of phenol and aniline on natural and organically modified montmorillonite: experiment and molecular modelling

Natural and intercalated Wyoming montmorillonite (MMT) with the tetramethylammonium (TMA) cations were used for the adsorption of phenol and aniline. Laboratory experiments characterised by adsorption isotherms were compared with the results of molecular modelling simulations. Aniline adsorbed itself strongly on MMT; while using the TMA intercalates (TMA-MMT), its adsorption decreased. On the contrary, the adsorption of phenol on TMA-MMT was moderately higher than on the MMT surface. The MMT surface models were described by empirical force field used in molecular mechanics and dynamics. The Burchart–Universal force field was used in the Cerius² modelling environment. The modelling results revealed the important role of water forming a moderately concentrated layer on the pure MMT surface. Water molecules enable the adsorption of aniline on MMT and, on the contrary, repel phenol molecules from MMT. In the case of TMA-MMT, lower amount of water near a silicate layer caused decrease in the aniline adsorption and, on the contrary, increase in the phenol adsorption.     

X-Ray studies of the ovomucoid-DHPC system

Complex of ovomucoid with 1,2 dihehadecyl-snglycero-3-phosphatidylcholine (DHPC) in water solution has been used as a model system for glycoprotein-lipid interactions.The structural parameters of this complex were determined with small angle-X-ray diffraction techniques. Knowing the repeat distance, the chemical composition of the association and the partial specific volumes of the components, the partial thickness of the glycoprotein, lipid and water layers can be determined and compared with the thickness of the lipid layers observed in pure lipid-water systems and lamellar associations in the absence of glycoprotein. The variation of the structural parameters at room temperature with the concentration of water was determined. Our results showed: the intersheet spacing increases from 112 to 157 Å, the thickness of the hydrocarbon chain layers decreases from 49 to 40Å and the thickness of glycoprotein layer increases from 62 to 100 Å. In this case the glycoprotein-lipid interaction appears to be of weak electrostatic nature and to involve mainly the polar regions of the structure. Fluorescence experiments have also been carried out to confirm the X-ray data.     

The effects of tetraalkylammonium salts on helix-coil transition parameters in natural and synthetic ribo- and deoxyribo-polynucleotides

Thermal transition profiles were recorded for a variety of natural and synthetic DNA and double-stranded RNA preparations in the presence of tetramethylammonium (TMA+) and tetraethylammonium (TEA+) cations. Double-stranded RNAs of natural origin, with GC contents of 50% exhibited the same profiles and Tm values as native DNA containing normal bases. Hence the tetraalkylammonium cations liquidate not only the effects of base composition, and the difference in stability between A-T and A-U base pairs (further confirmed by measurements with uracil-containing DNA from phage PBS-2), but also that of the 2'OH. In the presence of TMA+ cations, there is very marked enhancement of the stability of U-U base pairs in poly(rU) and poly(Um). In 2.4 M TEA, the 1:1 complex of poly(G) with poly (C) formed readily and melted reversibly with a Tm as low as 87 degrees C. At concentrations of TMA and TEA for which dTm/dXGC = 0, the Tm values for various phage DNA preparations containing atypical bases (phages T2, T4, phi e, phi W-14, PBS-2) differ appreciably from those with 'normal bases'. Analysis of these findings indicates that the selective interaction of TMA and TEA cations with A-T base pairs occurs in the minor groove of the DNA helix. The overall results show that the action of these quaternary ammonium cations is not due exclusively to preferential binding to A-T base pairs, but must involve other factors, including modifications of solvent structure. They also underline the utility of TMA and TEA solvent systems for placing in evidence transition profiles not accessible in other solvent systems.     

Interaction and properties of highly exfoliated soy protein/montmorillonite nanocomposites

The soy protein isolate (SPI)/ Na+ -montmorillonite (MMT) plastics were successfully prepared, and their structures and properties were characterized with X-ray diffraction, transmission electron microscopy, differential scanning calorimetry, thermogravimetric analysis, and tensile testing. The interactions between the soy protein macromolecules and MMT in aqueous media were analyzed with zeta-potential measurements, Fourier transform infrared spectroscopy, and electrostatic surface potential calculations. The results revealed that the heterogeneous distribution of the surface positive charges provided the positive-charge-rich domains for the soy globulins bearing net negative charges to anchor into the negatively charged MMT galleries. There were electrostatic attraction and hydrogen bonding interactions on the interfaces of the soy protein and MMT, which led to the good dispersion of the phyllosilicate layers in the protein matrix. The highly exfoliated MMT layers with a dimension of 1-2 nm in thickness were randomly dispersed in the protein matrix containing MMT lower than 12 wt %, whereas the intercalated structure was predominant when the MMT content was higher than 12 wt %. Consequently, the fine dispersion of the MMT layers and the strong interactions between SPI and MMT created the significant improvement of the mechanical strength and thermo-stability of the SPI/MMT plastics. In addition, a schematic illustration was proposed to describe the electrostatic interaction between SPI and MMT as well as the correlation between the interaction and structure in protein/clay systems.     

Structure and thermal behavior of the layered zincophosphate [NH3-CH2-CH(NH3)-CH3](ZnPO4)2

A zinc phosphate with the composition [NH₃-CH₂-CH(NH₃)-CH₃](ZnPO₄)₂, containing the doubly protonated 1,2-diaminopropane (abbr. HDAP), was synthesized by hydrothermal crystallization of zinc nitrate, phosphoric acid, 1,2-diaminopropane and trimethylenedipiperidine. The single crystal analysis shows a layered inorganic-organic structure built up of a sandwich-like motif of alternating inorganic layers and HDAP cations (trimethylenedipiperidine not being a constituent of the structure). The HDAP species are found to be disordered and serve as bridges between two adjacent inorganic layers which are separated by 3.95 Å. The bridging interaction occurs via a hydrogen-bonding network. The inorganic layer features a pattern of four-membered rings involving two ZnO₄ and two PO₄ tetrahedra connected by sharing O atoms. Thermal analysis shows that the compound is stable up to 370 °C and that the thermal decomposition of HDAP occurs in two steps between 370 and 460 °C, causing the collapse of the structure. The first decomposition step corresponds to ammonia removal which proceeds with a high activation energy (E_a = 282 kJ mol⁻¹). The high E_a value is mainly attributed to strong electrostatic interactions between organic cations and anionic inorganic layers, the disruption of the interactions being the main reason for structural collapse after the HDAP removal.     

The ultrastructure of multilamellar bodies and surfactant in the human lung

Summary Normal tissues from human lungs were dehydrated through Epon 812 resin to retain many of the lipids and carbohydrates in thin section. The three-dimensional structure of the multilamellar body was determined. The paired layer of phospholipid heads (PH) is 36Å thick; the layer of fatty-acid tails (FA) is 31Å, the same as reported previously for non-human primates and rodents. The human multilamellar body is apparently unique: the lamellae of the major focus divide into two or three lamellae; the matrix material of the core is without vesicular bodies and a projection core is present. When compared with those of the rat, human tissues contain a greater number of lamellar foci and fewer lamellae per focus. The presence of a peripheral layer of lamellae, an ever-present external limiting membrane, and the fusion of multilamellar bodies are also characteristic. Tubular myelin surfactant has the same appearance as in other mammals.Multilamellar bodies were observed in direct communication with Golgi vesicles. Their origin from multivesicular bodies and their maturation through secretion and exocytosis were demonstrated.Untransformed multilamellar bodies in the alveolar space demonstrated three periodicities (P): (1) compact regular lamellae, PH = 36Å, FA = 31Å, P = 66Å; (2) compact broad lamellae, PH = 72Å, FA = 22Å, P = 94Å; (3) loose lamellae, PH = 36Å, FA = 36Å, FA = 31Å with a variable interlamellar space.Appreciation is expressed to Nuket Olson and Phil Offenhauser for their technical assistance. Supported by a grant from the American Lung Association     

A repeating unit of higher order chromatin structure in chick red blood cell nuclei

The organization of nucleosomes in higher order chromatin structures has been studied by electron microscopy of chick red blood cell nuclei. Chromatin appears as a thick fiber with an average diameter of approximately 300 Å when prepared for electron microscopy in buffers which approximate physiological ionic strength. Progressive steps of disassembly of the thick fiber into individual nucleosomes could be induced either by ionic strength reduction or by tRNA treatment (which removes histone H1 and some non-histone chromosomal proteins). When disassembly was induced by ionic strength reduction in the presence of Mg⁺⁺ (or Ca⁺⁺), the lengths of the intermediate disassembly products were found to be multiples of 330 Å. The diameter of these structures was estimated to be 275 Å. This intermediate in the disassembly process is not observed if thick fiber disassembly is induced by ionic strength reduction in the absence of divalent cations. To investigate whether the higher order structural unit is present in the thick fiber at physiological ionic strengths, tRNA treatment was used to induce thick fiber disassembly under physiological monovalent ionic conditions. In this case, either with or without divalent cations, a supranucleosomal unit was found with dimensions similar to those given above. This data provides evidence for a slightly oblong supranucleosomal structure (330 × 275 Å) which forms a repeating unit in the chromatin thick fiber.     

Non-covalent interactions between cations in the crystal structure of [Pt{4′-(p-tolyl)trpy}Cl]SbF6, where trpy is 2,2′:6′,2″-terpyridine, underpin the salt’s complex solid-state luminescence spectrum

The synthesis and characterization of [Pt{4′-(p-tolyl)trpy}Cl]SbF₆ is described where trpy is 2,2′:6′,2″-terpyridine. A single crystal X-ray structure determination at 100 K shows that the cations are stacked in columns that comprise cations arranged in a staircase motif. Successive cations within a column are linked by π(trpy)-π(phenyl) stabilizing interactions; and each cation in one column is linked to a cation in an adjacent column by a weakly stabilizing Pt···Pt interaction. The Pt···Pt distance is 3.434(1) Å. The metrics governing non-covalent interactions between [Pt{4′-(aryl)trpy}Cl]⁺ cations have been analyzed for the present structure and related structures in the CSD (Cambridge Structural Database). Cation dimers cluster into three distinct groups based on their lateral shifts and, to a lesser extent, the angular parameters governing their relative displacements; the dominant grouping exhibits Pt···Pt and π(trpy)-π(trpy) stabilizing interactions. An emission spectrum recorded at 77 K on a solid sample of the compound is best interpreted as arising from the decay of three photoexcited states: a ³MLCT (MLCT = metal-to-ligand charge transfer) state; a ³MMLCT (MMLCT = metal-metal-to-ligand charge transfer) state, and an excimeric ³π-π^∗ state.     

The permeation of organic cations through cAMP-gated channels in mammalian olfactory receptor neurons

The permeation of monovalent organic cations through adenosine 3,5-cyclic monophosphate-(cAMP) activated channels was studied by recording macroscopic currents in excised inside-out membrane patches from the dendritic knobs of isolated mammalian olfactory receptor neurons (ORNs). Current-voltage relations were measured when bathing solution Na⁺ was replaced by monovalent organic cations. Permeability ratios relative to Na⁺ ions were calculated from changes in reversal potentials. Some of the small organic cations tested included ammonium (NH ₄ ⁺ ), hydroxylammonium and formamidinium, with relative permeability ratios of 1.41, 2.3 and 1.01 respectively. The larger methylated and ethylated ammonium ions studied included: DMA (dimethylammonium), TMA (tetramethylammonium) and TEA (tetraethylammonium) and they all had permeability ratios larger than 0.09. Even large cations such as choline, arginine and tris(hydroxymethyl)aminomethane (Tris) were appreciably permeant through the cAMP-activated channel with permeability ratios ranging from 0.19 to 0.7. The size of the permeating cations, as assessed by molecular weight, was a good predictor of the permeability. The permeability sequence of the cAMP-activated channel in our study was P_NH4 > P_Na > p_DMA > p_TMA > P_Choline > P_TEA. Higher permeability ratios of hydroxylammonium, arginine and tris(hydroxymethyl)aminomethane cannot be explained by ionic size alone. Our results indicate that: (i) cAMP-activated channels poorly select between monovalent cations; (ii) the pore dimension must be at least 6.5 × 6.5 Å, in order to allow TEA and Tris to permeate and (iii) molecular sieving must be an important mechanism for the permeation of large organic ions through the channels with specific ion binding playing a smaller role than in other structurally similar channels. In addition, the results clearly indicate that cyclic nucleotide-gated (CNG) channels in different cells are not the same, the olfactory CNG channel being different from that of the photoreceptors, particularly with respect to the permeation of large organic cations, which the ORN channels allow to permeate readily.This work was supported by the Australian Research Council of Australia.     

Crystal structure of bis(N-methylethylenediammonium) hexabromodicuprate(I)

The crystal structure of the title compound (C₃H₁₂N₂)₂Cu₂Br₆, is monoclinic, space group P2₁/n, with lattice constants a=8.222(2), b=11.214(2), c=10.646(2) Å, β=91.97(1)° and V=981.0(3) ų. The structure contains anionic Cu₂Br₆²⁻ dimers and N-methylethylenediammonium (henceforth MEDA²⁺) cations. The centrosymmetric dimer units are composed of two edge-shared CuBr₄ tetrahedra, with bridging Cu-Br distances 0.08 Å longer than the terminal distances. A pair of MEDA²⁺ cations hydrogen bond to each dimer via two of the -NH₃⁺ hydrogen atoms and one of the -NH₂⁺- hydrogen atoms. Additional hydrogen bonding between the cations and anions tie the structure together in a complex supramolecular network.     

Spatio-Temporal Analysis of the Accuracy of Tropical Multisatellite Precipitation Analysis 3B42 Precipitation Data in Mid-High Latitudes of China

Satellite-based precipitation data have contributed greatly to quantitatively forecasting precipitation, and provides a potential alternative source for precipitation data allowing researchers to better understand patterns of precipitation over ungauged basins. However, the absence of calibration satellite data creates considerable uncertainties for The Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA) 3B42 product over high latitude areas beyond the TRMM satellites latitude band (38°NS). This study attempts to statistically assess TMPA V7 data over the region beyond 40°NS using data obtained from numerous weather stations in 1998–2012. Comparative analysis at three timescales (daily, monthly and annual scale) indicates that adoption of a monthly adjustment significantly improved correlation at a larger timescale increasing from 0.63 to 0.95; TMPA data always exhibits a slight overestimation that is most serious at a daily scale (the absolute bias is 103.54%). Moreover, the performance of TMPA data varies across all seasons. Generally, TMPA data performs best in summer, but worst in winter, which is likely to be associated with the effects of snow/ice-covered surfaces and shortcomings of precipitation retrieval algorithms. Temporal and spatial analysis of accuracy indices suggest that the performance of TMPA data has gradually improved and has benefited from upgrades; the data are more reliable in humid areas than in arid regions. Special attention should be paid to its application in arid areas and in winter with poor scores of accuracy indices. Also, it is clear that the calibration can significantly improve precipitation estimates, the overestimation by TMPA in TRMM-covered area is about a third as much as that in no-TRMM area for monthly and annual precipitation. The systematic evaluation of TMPA over mid-high latitudes provides a broader understanding of satellite-based precipitation estimates, and these data are important for the rational application of TMPA methods in climatic and hydrological research.     

The fine structure of frozen-etched bacillus cereus spores

Summary The fine structure of Bacillus cereus spores was studied using the freeze-etching technique and compared with that already described in chemically fixed cells. Although the basic structures did not appear different, the freeze-etching technique permitted the examination of membrane surfaces and their involvement in sporulation. In this respect, some membranes were found to be covered with small 120 Å particles believed to represent multi-enzyme complexes, while other membranes appeared relatively smooth.One feature revealed by the freeze-etching technique and not demonstrated in chemically fixed cells, was the presence of relatively large (500 Å) vesicular structures. In many instances these vesicles were closely associated with different layers or membranes in the developing spore. While the role of these vesicular structures is as yet undetermined, their possible connection with the lytic process which liberates the spore from the sporangium, is discussed.     

Studying Liposomes by Tritium Bombardment

Bilayer liposomes from a mixture of dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylethanolamine (DPPC:DPPE=8:2, molar ratio) or DPPC labeled with ¹⁴C-DPPC (DPPC:¹⁴C-DPPC) were bombarded with thermally activated tritium atoms. The tritiated liposomes were hydrolyzed by phospholipase C, and the tritium incorporation into different parts of the bilayer along its thickness was determined. The tritium flux attenuation coefficients were calculated for the headgroup (k₁=0.176±0.032 Å^–1) and acylglycerol residue (k₂=0.046±0.004 Å^–1) layers indicating a preferential attenuation of the tritium flux in the headgroup region and relative transparence of the membrane hydrophobic part. The finding is potentially important to apply tritium bombardment for investigation of spatial organization of transmembrane proteins in their native lipid environment.     

The role of non-classical supramolecular interactions in the structures of 2-amino-4,6-dimethylpyridinium tetrahalocuprate (II) salts

The compounds [2-amino-4,6-dimethylpyridinium]₂CuCl₄ (1) and [2-amino-4,6-dimethylpyridinium]₂CuBr₄ (2) were prepared from acidic ethanolic media containing CuX₂ and [2-amino-4,6-dimethylpyridine] in the molar ratio 1:1. The compounds were characterized by IR and single-crystal X-ray diffraction and found to be isomorphous in the space group with V = 991.2(10) Å³ for (1) and 1059.26(12) Å³ for (2) . There is no significant difference in the non-classical N-H?X hydrogen bonding between (1) and (2). The anions show essentially the same extent of distortion from tetrahedral geometry with max./min. values for the X-Cu-X bond angles of 139.72(6)°/96.78(6)° for (1) and 139.43(4)°/96.64(3)° for (2). Each [CuX₄]²⁻ anion is hydrogen bonded nonsymmetrically to four cations. In this manner, ladder chains are formed that run along the b-axis, with planar cations falling parallel to the (2, 0, 1) plane. Weaker π-π interactions exist between cations from different chains with centroid to centroid distance of 4.07 Å in (1) and a long 4.594 Å in (2). The X-π electrostatic interactions are surprisingly stronger in (2) than in (1) with a Br to centroid of pyridinic ring distance of 3.890 Å compared with 3.996 Å for the chloride analogue.     

Molecular dynamics study of the swelling patterns of Na/Cs-, Na/Mg-montmorillonites and hydration of interlayer cations

Over the last two decades, the swelling properties of montmorillonite (MMT) have been studied in many experimental and simulation works, but less attention has been given to MMT containing a mixture of monovalent/monovalent and monovalent/bivalent cations in the interlayer spaces. We carried out a molecular dynamics simulation of the swelling patterns of Na-, Mg-, Na/Cs-, Na/Mg-MMT in an isobaric isothermal ensemble (NPT) at T = 300 K and p = 1 atm. The simulation reproduced a swelling pattern of Na-, Mg-, Na/Cs-, Na/Mg-MMT and the swelling curves obtained showed the difference between the hydration mechanisms of the type of MMT used in this study. We also found out that the differences in size and hydration energy of Na, Cs and Na, Mg ions have strong implications on the structure of interlayer water. This has led to the difference in the swelling curves of the simulated Na-, Mg-, Na/Cs- and Na/Mg-MMT. For Na/Cs-MMT, the hydration energy of Na cations increased compared to that in Na-MMT, the hydration energy of Cs cations decreased in Na/Cs-MMT compared to that in Cs-MMT and also for Na/Mg-MMT, the hydration energy of Na cations increased compared to that in Na-MMT and that of Mg cations decreased in comparison with that in Mg-MMT. The diffusion coefficient of Cs cations obtained in this simulation was higher than that of Mg and Na cations in Cs-, Mg- and Na-MMT, respectively. Cesium cations have been seen to have a low hydration energy compared to Na and Mg cations and can be used as a good inhibitor of Na-MMT swelling process.     

The ultrastructure of the blood capillaries in the mouse thyroid gland

Summary In the mouse thyroid gland the endothelium lining the blood capillaries is separated from the epithelial cells by a periendothelial space composed of three layers. Two of these are rather dense and localized close to the epithelium and endothelium, respectively. The third layer, interposed between the two dense layers, has a very low density. The dense layers, having each a thickness of 400–500 Å, show at high magnification in some places a lamellated structure. The middle layer varies in thickness and contains sometimes aggregates of a homogeneous material, circular bodies bordered by a membrane and, in single cases, fibrillar structures.The major part of the endothelial wall is very thin, only 200–600 Å. Within these thin parts discontinuities are observed, the endothelial cytoplasm being replaced by a more or less distinct membrane, about 50 Å thick. The dimension of the discontinuities is about 400 Å. The observations made are discussed.     

Tubuläre intranukleäre Einschlußkörper beiLinaria vulgaris,L. alpina (Scrophulariaceae) undIncarvillea variabilis (Bignoniaceae)

The epidermal nuclei of the ovary inLinaria vulgaris andL. alpina, and the nuclei in leaves ofIncarvillea variabilis often contain crystalloid, tubular inclusions. The tubuli in bothLinaria species have an average diameter of 200 Å with a width of 70 Å in the clear and are arranged in a higly organized manner: Parallel tubuli form layers which build up a crystal lattice. There are three directions of tubuli in each inclusion: In each layer they are aligned in an angle of 60° to those of the next, so that the tubuli of the fourth layer are in the same direction as those of the first one. InIncarvillea the tubuli (each with an average diameter of 220 Å, and 70 Å width in the clear) also exhibit compact packing, but their arrangement is not so highly ordered as inLinaria.

     

Hydrothermal synthesis and structural investigation of silver magnesium complex of benzenehexacarboxylic acid (mellitic acid), Ag2Mg2[C6(COO)6] · 8H2O with two-dimensional layered structure

Crystal and molecular structure of silver magnesium mellitate, Ag₂Mg₂[C₆(COO)₆] · 8H₂O, was synthesized hydrothermally and characterized by X-ray structure analysis. The complex crystallizes in the monoclinic system, space group P2/n, with unit cell dimensions of a=7.4347(2), b=9.9858(2), c=14.4248(3) Å, β=99.2429(5)°, V=1055.01(4) ų, and Z=2. The structure was solved and refined to R=0.036 (R_w=0.045) for 1707 independent reflections [I_o>2σ(I_o)]. The Ag cations are coordinated by six carboxylic oxygen atoms of mellitate anions with composition of [C₆(COO)₆]⁶⁻ on the (1 0 1) plane; each mellitate anion linking three neighboring Ag distorted trigonal prisms produces a two-dimensional layered structure parallel to (1 0 1). The Mg cations, which are coordinated by four water molecules and two carboxylic oxygen atoms, are intercalated between the two-dimensional layer stacks. The carboxylate group coordinated to Mg and Ag cations serve as a tridentate ligand in that structure. The number of water molecules incorporated into the mellitate compound is controlled mainly by ionic radii of metal cation in the structure. Furthermore, the ionic radii of metal cations in the mellitate compound play an essential role in arrangement of mellitate anions in the structure, whether as a one-dimensional infinite chain, a two-dimensional layered structure, or a three-dimensional framework structure.