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1.  Poly[μ-aqua-aqua-μ4-naphthalene-1,8-dicarboxyl­ato-barium]: a layer structure 
The title compound, [Ba(C12H6O4)(H2O)2]n, is represented by a layer-like structure built of BaO8 polyhedra. The asymmetric unit contains a Ba2+ ion, half a coordinating water mol­ecule and half a μ4-bridging naphthalene-1,8-dicarboxyl­ate (1,8-nap) ligand, the whole structure being generated by twofold rotational symmetry. The carboxyl­ate groups of the 1,8-nap ligands act as bridges linking four Ba2+ ions, while each Ba2+ ion is eight-coordinated by O atoms from four 1,8-nap ligands and two coordinating water mol­ecules. In the crystal, there are O—H⋯O hydrogen bonds involving the water mol­ecules and carboxyl­ate O atoms in the BaO8 polyhedra. Each BaO8 polyhedron is connected via corner-sharing water O atoms or edge-sharing ligand O atoms, forming a sheet parallel to the bc plane. These sheets stack along the a-axis direction and are connected via van der Waals forces only. The naphthalene groups protrude above and below the layers of the BaO8 polyhedra and there are voids of ca 208 Å3 bounded by these groups. No residual electron density was found in this region. The crystal studied was twinned by pseudo-merohedry, with a refined twin component ratio of 0.5261 (1):0.4739 (1).
PMCID: PMC3629495  PMID: 23634013
2.  Ba2Sb4GeS10  
The title quaternary compound, dibarium tetra­anti­mony germanium deca­sulfide, Ba2Sb4GeS10, crystallizes in a novel three-dimensional ∞ 3[Sb4GeS10]4− network structure, which is composed of triangular pyramidal SbS3 (site symmetry m..), distorted SbS5 (m..) polyhedra and regular GeS4 (-4..) tetra­hedra. The SbS3 and SbS5 units are connected with each other through corner- and edge-sharing, forming a Sb4S10 layer in the ab plane. The GeS4 tetra­hedra further bridge two neighbouring Sb4S10 layers, forming a three-dimensional ∞ 3[Sb4GeS10]4− network. The Ba2+ cation (..2) is located between two Sb4S10 layers and is coordinated by ten S atoms with Ba—S bond lengths in the range 3.2505 (9)–3.4121 (2) Å.
PMCID: PMC3647782  PMID: 23723748
3.  The lanthanum(III) molybdate(VI) La4Mo7O27  
Crystals of the ortho­rhom­bic phase La4Mo7O27 (lanthanum molybdenum oxide) were obtained from a non-stoichiometric melt in the pseudo-ternary system La2O3–MoO3–B2O3. In the crystal structure, distorted square-anti­prismatic [LaO8] and monocapped square-anti­prismatic [LaO9] polyhedra are connected via common edges and faces into chains along [010]. These chains are arranged in layers that alternate with layers of [MoO4] and [MoO5] polyhedra parallel to (001). In the molybdate layers, a distorted [MoO5] trigonal bipyramid is axially connected to two [MoO4] tetra­hedra, forming a [Mo3O11] unit.
PMCID: PMC2977117  PMID: 21583295
4.  Na7Mg13Nd(PO4)12  
Investigations of the quasi-ternary system Na3PO4–Mg3(PO4)2–NdPO4 allowed us to obtain the new phosphate hepta­sodium trideca­magnesium neodymium dodeca­kis­phosphate, Na7Mg13Nd(PO4)12, by applying a flux method. The crystal structure is isotypic with that of the previously reported Na7Mg13 Ln(PO4)12 (Ln = Eu, La) compounds. It consists of a complex three-dimensional framework built up from an NdO8 polyhedron (m symmetry), an MO6 octa­hedron statistically occupied by M = Mg and Na, and eight MgOx (x = 5, 6) polyhedra (four with site symmetry m), linked either directely by sharing corners, edges and faces, or by one of the eight unique PO4 tetra­hedra through common corners. Two of the PO4 tetra­hedra are statisticaly disordered over a mirror plane. The whole structure can be described as resutling from an assembly of two types of structural units, viz [Mg4 MP4O22]∞ 2 layers extending parallel to (100) and stacked along [100], and [Mg4NdP4O36]∞ 1 undulating chains running along the [010] direction. The six different Na+ cations (five with site symmetry m and one with 0.5 occupancy) are situated in six distinct cavities delimited by the framework. The structure was refined from data of a racemic twin.
PMCID: PMC3379054  PMID: 22719275
5.  MnBa2(HPO4)2(H2PO4)2  
Crystals of manganese(II) dibarium bis­(hydrogenphosphate) bis­(dihydrogenphosphate), MnBa2(HPO4)2(H2PO4)2, were obtained by hydro­thermal synthesis. The title compound is isotypic with its CdII and CaII analogues. The structure is built up of an infinite {[Mn(HPO4)2(H2PO4)2]4−}n chain running along [100], which consists of alternate MnO6 octa­hedra and [PO4] tetra­hedra, in which the centrosymmetric MnO6 octa­hedra share their four equatorial O-atom corners with tetra­hedral [PO3(OH)] groups and their two axial apices with tetra­hedral [PO2(OH)2] groups. These chains are held together by BaO9 coordination polyhedra, developing into a three-dimensional structure. The O—H⋯O hydrogen bonds additionally stabilize the structural set-up. Due to the ionic radius of Mn2+ being much smaller than those of Ca2+ and Cd2+, this may imply that their adopted structure type has a great tolerance for incorporating various ions and the exploitation of more diverse compounds in the future is encouraged.
PMCID: PMC3379057  PMID: 22719278
6.  The aluminoarsenate Na1.67K1.33Al3(AsO4)4  
The title compound, sodium potassium trialuminium tetra­kis­(orthoarsenate), was prepared by solid-state reactions. The anionic framework consists of corrugated layers parallel to (010) and is made up of corner-sharing AlO6 octa­hedra (site symmetries .2. and 2/m..) that are connected to isolated AsO4 tetra­hedra (site symmetries .2. and m..) through edge- and corner-sharing. The alkali cations are occupationally disordered. The two K+ cations [site symmetries .2. and m..; occupancies 0.314 (7) and 0.035 (12)] are situated in the inter­layer space, whereas the smaller Na+ cations [both with site symmetry m..; occupancies = 0.725 (14) and 0.112 (14)] are located in the cavities of the anionic framework. The K+ cations are surrounded by six and seven O atoms, the Na+ cations by seven and nine O atoms. The resulting coordination polyhedra of the two types of cations are highly distorted.
PMCID: PMC3914036  PMID: 24526941
7.  An ortho­rhom­bic polymorph of the ultraphosphate YP5O14  
Single crystals of yttrium penta­phosphate(V), YP5O14, were obtained by solid-state reaction. The ortho­rhom­bic title compound belongs to the family of ultraphosphates and is the second polymorph of this composition. It is isotypic with its Ho and Er analogues. The structure contains two bridging Q 2-type PO4 tetra­hedra and one branching Q 3-type PO4 tetra­hedron, leading to infinite ultraphosphate ribbons running along the a axis. The coordination polyhedron around the Y3+ cation may be described as distorted bicapped trigonal-prismatic. The YO8 polyhedra are isolated from each other. They are linked by corner-sharing to the O atoms of six Q 2-type and of two Q 3-type PO4 tetra­hedra into a three-dimensional framework.
PMCID: PMC2968816  PMID: 21582306
8.  The iron phosphate CaFe3(PO4)3O 
A new iron phosphate, calcium triiron(III) tris­(phosphate) oxide, CaFe3(PO4)3O, has been isolated and shown to exhibit a three-dimensional structure built by FeO6 octa­hedra, FeO5 trigonal bipyramids and PO4 tetra­hedra. The FeOx (x = 5, 6) polyhedra are linked through common corners and edges, forming [Fe6O28]∞ chains with branches running along [010]. Adjacent chains are connected by the phosphate groups via common corners and edges, giving rise to a three-dimensional framework analogous to those of the previously reported SrFe3(PO4)3O and Bi0.4Fe3(PO4)3O structures, in which the Ca2+ cations occupy a single symmetry non-equivalent cavity.
PMCID: PMC2977148  PMID: 21583300
9.  Na3Co2(As0.52P0.48)O4(As0.95P0.05)2O7  
The title compound, trisodium dicobalt(II) (arsenate/phosphate) (diarsenate/diphosphate), was prepared by a solid-state reaction. It is isostructural with Na3Co2AsO4As2O7. The framework shows the presence of CoX22O12 (X2 is statistically disordered with As0.95P0.05) units formed by sharing corners between Co1O6 octa­hedra and X22O7 groups. These units form layers perpendicular to [010]. Co2O6 octa­hedra and X1O4 (X1 = As0.54P0.46) tetra­hedra form Co2X1O8 chains parallel to [001]. Cohesion between layers and chains is ensured by the X22O7 groups, giving rise to a three-dimensional framework with broad tunnels, running along the a- and c-axis directions, in which the Na+ ions reside. The two Co2+ cations, the X1 site and three of the seven O atoms lie on special positions, with site symmetries 2 and m for the Co, m for the X1, and 2 and m (× 2) for the O sites. One of two Na atoms is disordered over three special positions [occupancy ratios 0.877 (10):0.110 (13):0.066 (9)] and the other is in a general position with full occupancy. A comparison between structures such as K2CdP2O7, α-NaTiP2O7 and K2MoO2P2O7 is made. The proposed structural model is supported by charge-distribution (CHARDI) analysis and bond-valence-sum (BVS) calculations. The distortion of the coordination polyhedra is analyzed by means of the effective coordination number.
PMCID: PMC3884975  PMID: 24454150
10.  Barium dierbium(III) tetra­sulfide 
Barium dierbium(III) tetra­sulfide, BaEr2S4, crystallizes with four formula units in the ortho­rhom­bic space group Pnma in the CaFe2O4 structure type. The asymmetric unit contains two Er, one Ba, and four S atoms, each with .m. site symmetry. The structure consists of channels formed by corner- and edge-sharing ErS6 octa­hedra in which Ba atoms reside. The resultant coordination of Ba is that of a bicapped trigonal prism.
PMCID: PMC3588518  PMID: 23476480
11.  Thulium nickel/lithium distannide, TmNi1−xLixSn2 (x = 0.035) 
The quaternary thulium nickel/lithium distannide, TmNi1−xLixSn2 (x = 0.035), crystallizes in the ortho­rhom­bic LuNiSn2 structure type. The asymmetric unit contains three Tm sites, six Sn sites, two Ni sites and one Ni/Li site [relative occupancies = 0.895 (8):0.185 (8)]. Site symmetries are .m. for all atoms. The 17-, 18- and 19-vertex distorted pseudo-Frank–Kasper polyhedra are typical for all Tm atoms. Four Sn atoms are enclosed in a 12-vertex deformed cubo­octa­hedron, and another Sn atom is enclosed in a penta­gonal prism with three added atoms. A tricapped trigonal prism is typical for a further Sn atom. The coordination number for all Ni atoms and Ni/Li statistical mixtures is 12 (fourcapped trigonal prism [Ni/LiTm5Sn5]). Tm atoms form the base of a prism and Ni/Li atoms are at the centres of the side faces of an [SnTm6Ni/Li3] prism. These isolated prisms are implemented into three-dimensional-nets built out of Sn atoms. Electronic structure calculations using TB-LMTO-ASA suggest that the Tm and Ni/Li atoms form positively charged n[TmNi/Li]m+ polycations which compensate the negative charge of 2n[Sn]m− polyanions. Analysis of the inter­atomic distances and electronic structure calculations indicate the dominance of a metallic type of bonding.
PMCID: PMC3884236  PMID: 24454012
12.  Na3Co2(AsO4)(As2O7): a new sodium cobalt arsenate 
In the title compound, tris­odium dicobalt arsenate diarsenate, Na3Co2AsO4As2O7, the two Co atoms, one of the two As and three of the seven O atoms lie on special positions, with site symmetries 2 and m for the Co, m for the As, and 2 and twice m for the O atoms. The two Na atoms are disordered over two general and special positions [occupancies 0.72 (3):0.28 (3) and 0.940 (6):0.060 (6), respectively]. The main structural feature is the association of the CoO6 octa­hedra in the ab plane, forming Co4O20 units, which are corner- and edge-connected via AsO4 and As2O7 arsenate groups, giving rise to a complex polyhedral connectivity with small tunnels, such as those running along the b- and c-axis directions, in which the Na+ ions reside. The structural model is validated by both bond-valence-sum and charge-distribution methods, and the distortion of the coordination polyhedra is analyzed by means of the effective coordination number.
PMCID: PMC3393142  PMID: 22807699
13.  Agardite-(Y), Cu2+ 6Y(AsO4)3(OH)6·3H2O 
Agardite-(Y), with a refined formula of Cu2+ 5.70(Y0.69Ca0.31)[(As0.83P0.17)O4]3(OH)6·3H2O [ideally Cu2+ 6Y(AsO4)3(OH)6·3H2O, hexa­copper(II) yttrium tris­(arsenate) hexa­hydroxide trihydrate], belongs to the mixite mineral group which is characterized by the general formula Cu2+ 6 A(TO4)3(OH)6·3H2O, where nine-coordinated cations in the A-site include rare earth elements along with Al, Ca, Pb, or Bi, and the T-site contains P or As. This study presents the first structure determination of agardite-(Y). It is based on the single-crystal X-ray diffraction of a natural sample from Jote West mine, Pampa Larga Mining District, Copiapo, Chile. The general structural feature of agardite-(Y) is characterized by infinite chains of edge-sharing CuO5 square pyramids (site symmetry 1) extending down the c axis, connected in the ab plane by edge-sharing YO9 polyhedra (site symmetry -6..) and corner-sharing AsO4 tetra­hedra (site symmetry m..). Hy­droxyl groups occupy each corner of the CuO5-square pyramids not shared by a neighboring As or Y atom. Each YO9 polyhedron is surrounded by three tubular channels. The walls of the channels, parallel to the c axis, are six-membered hexa­gonal rings comprised of CuO5 and AsO4 polyhedra in a 2:1 ratio, and contain free mol­ecules of lattice water.
PMCID: PMC3884410  PMID: 24426980
14.  The aluminoarsenate K1.8Sr0.6Al3(AsO4)4  
The title compound, potassium strontium trialuminium tetra­arsenate, was prepared by solid-state reaction. The structure consists of AlO6 octa­hedra (site symmetries 2.. and 2/m) and two AsO4 tetra­hedra (.2. and m..) sharing corners and edges to form a two-dimensional structure parallel to (010). The cations are occupationally disordered and are located in the interlayer space. For both types of cations, distorted coordination polyhedra are observed.
PMCID: PMC3344283  PMID: 22590049
15.  Dipotassium dialuminium cyclo­octa­phosphate 
Single crystals of the title compound, K2Al2P8O24, were obtained by solid-state reaction. The monoclinic structure is isotypic with that of the GaIII analogue and is built of eight-membered phosphate ring anions P8O24 8− (2/m symmetry) isolated from each other and further linked by isolated AlO6 octa­hedra ( symmetry) by sharing corners. Each AlO6 octa­hedron is linked to four P8O24 8− rings in such a way that two rings are linked through bidentate diphosphate groups attached in the cis positions on two opposite parallel edges of the octa­hedron. The two other rings are linked via corner-sharing to the two remaining corners in the trans positions of the AlO6 octa­hedron. Each P8O24 8− ring anion is linked to eight AlO6 octa­hedra. More accurately, each ring anion is linked to four AlO6 octa­hedra through bidentate diphosphate groups attached in the cis positions to the AlO6 octa­hedron and to the four remaining octa­hedra by sharing corners. This three-dimensional linkage delimits channels running parallel to [001] in which the ten-coordinated K+ cations (2 symmetry) are distributed over two columns. These columns alternate with empty octa­gonally-shaped channels expanding through the P8O24 8− ring anions.
PMCID: PMC3007075  PMID: 21587666
16.  Redetermination of Ba2CdTe3 from single-crystal X-ray data 
The previous structure determination of the title compound, dibarium tritelluridocadmate, was based on powder X-ray diffraction data [Wang & DiSalvo (1999 ▶). J. Solid State Chem. 148, 464–467]. In the current redetermination from single-crystal X-ray data, all atoms were refined with anisotropic displacement parameters. The previous structure report is generally confirmed, but with some differences in bond lengths. Ba2CdTe3 is isotypic with Ba2 MX 3 (M = Mn, Cd; X = S, Se) and features 1 ∞[CdTe2/2Te2/1]4− chains of corner-sharing CdTe4 tetra­hedra running parallel [010]. The two Ba2+ cations are located between the chains, both within distorted monocapped trigonal–prismatic coordination polyhedra. All atoms in the structure are located on a mirror plane.
PMCID: PMC3470123  PMID: 23125567
17.  Crystal structures of Na2SeO4·1.5H2O and Na2SeO4·10H2O 
The crystal structures of the 1.5- and 10-hydrates of Na2SeO4 are isotypic with those of the corresponding chromates.
The crystal structures of Na2SeO4·1.5H2O (sodium selenate sesquihydrate) and Na2SeO4·10H2O (sodium selenate deca­hydrate) are isotypic with those of Na2CrO4·1.5H2O and Na2 XSeO4·10H2O (X = S, Cr), respectively. The asymmetric unit of the sesquihydrate contains two Na+ cations, one SeO4 tetra­hedron and one and a half water mol­ecules, the other half being generated by twofold rotation symmetry. The coordination polyhedra of the cations are a distorted monocapped octa­hedron and a square pyramid; these [NaOx] polyhedra are linked through common edges and corners into a three-dimensional framework structure, the voids of which are filled with the Se atoms of the SeO4 tetra­hedra. The structure is consolidated by O—H⋯O hydrogen bonds between coordinating water mol­ecules and framework O atoms. The asymmetric unit of the deca­hydrate consists of two Na+ cations, one SeO4 tetra­hedron and ten water mol­ecules. Both Na+ cations are octa­hedrally surrounded by water mol­ecules and by edge-sharing condensed into zigzag chains extending parallel to [001]. The SeO4 tetra­hedra and two uncoordinating water mol­ecules are situated between the chains and are connected to the chains through an intricate network of medium-strength O—H⋯O hydrogen bonds.
PMCID: PMC4158548  PMID: 25249853
isotypism; sodium selenate; salt hydrates; crystal structure
18.  Dilithium manganese(II) catena-tetrakis(polyphosphate), Li2Mn(PO3)4  
The poly-phosphate Li2Mn(PO3)4 was synthesized and its structure characterized from powder diffraction data by Averbuch-Pouchot & Durif [J. Appl. Cryst. (1972), 5, 307–308]. These authors showed that the structure of this phosphate is isotypic to that of Li2Cd(PO3)4, as confirmed by the present work. The structure is built from infinite zigzag polyphosphate chains, [(PO3)−]n, extending along [010]. These polyphosphate chains are connected by sharing vertices with MnO6 octa­hedra (site symmetry .m.) and Li2O7 polyhedra, which form also chains parallel to [010]. Adjacent chains are linked by common vertices of polyhedra in such a way as to form porous layers parallel to (100). The three-dimensional framework delimits empty channels extending along [010].
PMCID: PMC3914032  PMID: 24526937
19.  Rietveld refinement of whitlockite-related K0.8Ca9.8Fe0.2(PO4)7  
The title compound, K0.8Ca9.8Fe0.2(PO4)7 (potassium deca­calcium iron hepta­phosphate), belongs to the whitlockite family. The structure is built up from several types of metal–oxygen polyhedra: two [CaO8], one [CaO7] and one [(Ca/Fe)O6] polyhedron with a mixed Ca/Fe occupancy in a 0.8:0.2 ratio, as well as three tetra­hedral [PO4] units. Of the 18 sites in the asymmetric unit, the site with the mixed Ca/Fe occupation, the K site, one P and one O site are on special positions 6a with 3 symmetry, whereas all other sites are on general positions 18b. The linkage of metal–oxygen polyhedra and [PO4] tetra­hedra via edges and corners results in formation of a three-dimensional framework with composition [Ca9.8Fe0.2(PO4)7]0.8−. The remaining K atoms (site-occupation factor = 0.8) are located in large closed cavities and are nine-coordinated by oxygen.
PMCID: PMC2979107  PMID: 21578988
20.  Redetermination of EuScO3  
Single crystals of europium(III) scandate(III), with ideal formula EuScO3, were grown from the melt using the micro-pulling-down method. The title compound crystallizes in an ortho­rhom­bic distorted perovskite-type structure, where Eu occupies the eightfold coordinated A sites (site symmetry m) and Sc resides on the centres of corner-sharing [ScO6] octa­hedra (B sites with site symmetry ). The structure of EuScO3 has been reported previously based on powder diffraction data [Liferovich & Mitchell (2004). J. Solid State Chem. 177, 2188–2197]. The results of the current redetermination based on single-crystal diffraction data shows an improvement in the precision of the structral and geometric parameters and reveals a defect-type structure. Site-occupancy refinements indicate an Eu deficiency on the A site coupled with O defects on one of the two O-atom positions. The crystallochemical formula of the investigated sample may thus be written as A(□0.032Eu0.968)BScO2.952.
PMCID: PMC2968298  PMID: 21581742
21.  A novel monoclinic phase of impurity-doped CaGa2S4 as a phosphor with high emission intensity 
In the solid-state synthesis of impurity-doped CaGa2S4, calcium tetra­thio­digallate(III), a novel phosphor material (denominated as the X-phase), with monoclinic symmetry in the space group P21/a, has been discovered. Its emission intensity is higher than that of the known ortho­rhom­bic polymorph of CaGa2S4 crystallizing in the space group Fddd. The asymmetric unit of the monoclinic phase consists of two Ca, four Ga and eight S sites. Each of the Ca and Ga atoms is surrounded by seven and four sulfide ions, respectively, thereby sharing each of the sulfur sites with the nearest neighbours. In contrast, the corresponding sites in the ortho­rhom­bic phase are surrounded by eight and four S atoms, respectively. The photoluminescence peaks from Mn2+ and Ce3+ in the doped X-phase, both of which are supposed to replace Ca2+ ions, have been observed to shift towards the high energy side in comparison with those in the ortho­rhom­bic phase. This suggests that the crystal field around the Mn2+ and Ce3+ ions in the X-phase is weaker than that in the ortho­rhom­bic phase.
PMCID: PMC3379052  PMID: 22719273
22.  Lithio­marsturite, LiCa2Mn2Si5O14(OH) 
Lithio­marsturite, ideally LiCa2Mn2Si5O14(OH), is a member of the pectolite–pyroxene series of pyroxenoids (hydro­pyroxenoids) and belongs to the rhodonite group. A previous structure determination of this mineral based on triclinic symmetry in space group P by Peacor et al. [Am. Mineral. (1990), 75, 409–414] converged with R = 0.18 without reporting any information on atomic coordinates and displacement param­eters. The current study redetermines its structure from a natural specimen from the type locality (Foote mine, North Carolina) based on single-crystal X-ray diffraction data. The crystal structure of lithio­marsturite is characterized by ribbons of edge-sharing CaO6 and two types of MnO6 octa­hedra as well as chains of corner-sharing SiO4 tetra­hedra, both extending along [110]. The octa­hedral ribbons are inter­connected by the rather irregular CaO8 and LiO6 polyhedra through sharing corners and edges, forming layers parallel to (1), which are linked together by the silicate chains. Whereas the coordination environments of the Mn and Li cations can be compared to those of the corresponding cations in nambulite, the bonding situations of the Ca cations are more similar to those in babingtonite. In contrast to the hydrogen-bonding scheme in babingtonite, which has one O atom as the hydrogen-bond donor and a second O atom as the hydrogen-bond acceptor, our study shows that the situation is reversed in lithio­marsturite for the same two O atoms, as a consequence of the differences in the bonding environments around O atoms in the two minerals.
PMCID: PMC3238580  PMID: 22199471
23.  Diytterbium(II) lithium indium(III) digermanide, Yb2LiInGe2  
The title compound, Yb2LiInGe2, a new ordered quaternary inter­metallic phase, crystallizes with the ortho­rhom­bic Ca2LiInGe2 type (Pearson code oP24). The crystal structure contains six crystallographically unique sites in the asymmetric unit, all in special positions with site symmetry .m.. The structure is complex and based on [InGe4] tetra­hedra, which share corners in two directions, forming layers parallel to (001). Yb atoms fill square-pyramidal (Yb1) and octa­hedral (Yb2) inter­stices between the [InGe4/2] layers, while the small Li+ atoms fill tetra­hedral sites.
PMCID: PMC2979241  PMID: 21578989
24.  A two-dimensional organic–inorganic hybrid compound, poly[(ethylenediamine)tri-μ-oxido-oxidocopper(II)molybdenum(VI)] 
A new organic–inorganic two-dimensional hybrid compound, [CuMoO4(C2H8N2)], has been hydro­thermally synthesized at 443 K. The unit cell contains layers composed of CuN2O4 octa­hedra and MoO4 tetra­hedra. Corner-sharing MoO4 and CuN2O4 polyhedra form CuMoO4 bimetallic sites that are joined together through O atoms, forming an edge-sharing Cu2Mo2O4 chain along the c axis. The one-dimensional chains are further linked through bridging O atoms that join the Cu and Mo atoms into respective chains along the b axis, thus establishing layers in the bc plane. The ethyl­enediamine ligand is coordinated to the Cu atom through its two N atoms and is oriented perpendicularly to the two-dimensional –Cu—O—Mo– layers. The average distance between adjacent layers, as calculated by consideration of the closest and furthest distances between two layers, is 8.7 Å. The oxidation states of the Mo and Cu atoms of VI and II, respectively, were confirmed by bond-valence sum calculations.
PMCID: PMC2959353  PMID: 21200997
25.  Elastic energy of polyhedral bilayer vesicles 
In recent experiments the spontaneous formation of hollow bilayer vesicles with polyhedral symmetry has been observed. On the basis of the experimental phenomenology it was suggested that the mechanism for the formation of bilayer polyhedra is minimization of elastic bending energy. Motivated by these experiments, we study the elastic bending energy of polyhedral bilayer vesicles. In agreement with experiments, and provided that excess amphiphiles exhibiting spontaneous curvature are present in sufficient quantity, we find that polyhedral bilayer vesicles can indeed be energetically favorable compared to spherical bilayer vesicles. Consistent with experimental observations we also find that the bending energy associated with the vertices of bilayer polyhedra can be locally reduced through the formation of pores. However, the stabilization of polyhedral bilayer vesicles over spherical bilayer vesicles relies crucially on molecular segregation of excess amphiphiles along the ridges rather than the vertices of bilayer polyhedra. Furthermore, our analysis implies that, contrary to what has been suggested on the basis of experiments, the icosahedron does not minimize elastic bending energy among arbitrary polyhedral shapes and sizes. Instead, we find that, for large polyhedron sizes, the snub dodecahedron and the snub cube both have lower total bending energies than the icosahedron.
PMCID: PMC3236088  PMID: 21797397

Results 1-25 (27644)