Kwang-Hwa Lii

Syntheses, crystal structures and magnetic properties of two novel layered compounds: [Fe3(C2O4)3(4,4′-bpy)4] and [Co(C2O4)(4,4′-bpy)] (4,4′-bpy = 4,4′-bipyridine)†

The combination of 4,4′-bipyridine (4,4′-bpy) and oxalate ligands has resulted in the formation of two novel layered compounds [Fe3(C2O4)3(4,4′-bpy)4] 1 and [Co(C2O4)(4,4′-bpy)] 2. Both compounds exhibit two-dimensional layer structures. That of 1 consists of iron(II) oxalate chains, with the terminal and the bridging 4,4′-bpy stacking alternately between the chains. The structure of 2 contains linear chains of cobalt(II) oxalate which are cross-linked by 4,4′-bpy molecules in a perpendicular manner, leading to square grid sheets with rectangular windows. Magnetic measurements reveal that weak antiferromagnetic interactions are mediated in both compounds.

One- and two-dimensional materials containing vanadium oxide: structures and magnetic properties of Cu(dien)V2O6·H2O and Ni(dien)V2O6 (dien = diethylenetriamine)†

The structures of a one-dimensional compound Cu(dien)V2O6·H2O 1 and a two-dimensional compound Ni(dien)V2O6 2, where dien is diethylenetriamine, have been determined by X-ray diffraction. The former is composed of corner-sharing VO4 tetrahedra chains, with Cu(dien)2+ fragments attached to every other VO4 unit. The latter has a layer structure with the V4O12 tetramers connected by edge-shared Ni2(µ-O)2(dien)24+ dimers. The layers are further stacked to form one-dimensional channels along the [001] direction. Magnetic susceptibility measurements for both compounds have been performed down to 2 K. Paramagnetic behavior is observed in 1, whereas ferromagnetic interaction is found to be dominant in 2.

Na7Fe4(PO4)6: a mixed-valence iron phosphate containing a tetramer of edge-sharing FeO6 octahedra

A novel mixed-valence iron phosphate, Na7Fe4(PO4)6, has been synthesized by a high-temperature, high-pressure hydrothermal method and characterized by single-crystal X-ray diffraction and Mossbauer spectroscopy. The compound crystallizes in the trigonal space group Rc with a= 13.392(2), c= 17.858(3)A, U= 2773.7(8)A3, Z= 6 and R= 0.0179. The structure consists of tetrameric units of edge-sharing FeO6 octahedra, which are connected by corner-sharing PO4 tetrahedra to form a three-dimensional framework structure, enclosing a network of cavities where the sodium cations reside. Mossbauer spectroscopy supports the presence of one FeII and three FeIII in a tetrameric unit.

CsFe3(PO4)3(OH2)2: a mixed-valence iron phosphate containing trimeric units of iron–oxygen polyhedra

A mixed-valence iron phosphate, CsFe3(PO4)3(OH2)2, has been synthesized hydrothermally and characterized by single-crystal X-Ray diffraction and Mossbauer spectroscopy. The compound crystallizes in the monoclinic space group C2/c with a= 13.435(2), b= 10.488(1), c= 9.024(2)A, β= 108.60(1)°, U= 1205.1(3)A3 and Z= 4. The structure consists of a three-dimensional framework of vertex-sharing FeIIIO5 trigonal bipyramids, FeIIO4(OH2)2 octahedra and PO4 tetrahedra, enclosing a network of cavities, where the caesium cations reside. Mossbauer spectroscopy confirms the presence of one FeII and two FeIII.

Hydrothermal synthesis, crystal structure and ionic conductivity of Ag2VO2PO4: a new layered phosphate of vanadium(V)

A new dioxovanadium(V) phosphate, Ag2VO2PO4, has been synthesised hydrothermally at 230 °C and characterized by single-crystal X-ray diffraction. The compound crystallizes in the monoclinic space group C2/m with a= 12.431(3), b= 6.298(1), c= 6.300(2)A, β= 90.38(2)°, Z= 4 and R= 0.026. The structure consists of layers of dimers of edge-sharing VO6 octahedra and PO4 tetrahedra, extending parallel to the (001) crystallographic plane with silver ions between the layers. The structural relationship with BaVO2PO4 is discussed. Alternating current impedance measurements on Ag2VO2PO4 indicate that the ionic conductivity at 375 °C is 1 × 10–4Ω–1 cm–1 with an activation energy of 47 kJ mol–1.

Organically templated inorganic/organic hybrid materials: hydrothermal synthesis and structural characterization of [C4H12N2][In2(C2O4)(HPO4)3]·H2O

The synthesis and characterization of a novel inorganic/organic hybrid material is described; the 3-D framework consists of InO6 octahedra which are linked by inorganic phosphate and organic oxalate anions to generate intersecting tunnels in which piperazinium cations and water molecules reside.

[HN(CH2CH2)3NH]3[Fe8(HPO4)12(PO4)2(H2O)6]: an organically templated iron phosphate with apillared layer structure

An organically templated iron phosphate, [HN(CH 2 CH 2 ) 3 NH] 3 [Fe 8 (HPO 4 ) 12 (PO 4 ) 2 (H 2 O) 6 ], has been synthesized under solvothermal conditions and characterized by single-crystal X-ray diffraction, Mossbauer spectroscopy and thermogravimetric analysis. The compound crystallizes in the trigonal space group Pc1 (no. 165) with a = 13.5274(5), c = 19.2645(6) A, U = 3052.9(3) A 3 and Z = 2. The structure consists of layers of corner-sharing FeO 6 and FeO 5 (OH 2 ) octahedra and PO 4 and PO 3 (OH) tetrahedra which are pillared through additional FeO 6 octahedra to form a three-dimensional framework structure. The framework contains a two-dimensional array of intersecting channels in which the charge compensating diprotonated 1,4-diazabicyclo[2.2.2]octane cations reside. The framework is closely related to that of an imidazole encapsulating indium phosphate, [H 3 O][C 3 N 2 H 5 ] 3 [In 8 (HPO 4 ) 14 (H 2 O) 6 ]·5H 2 O.

RbIn(OH)PO4: an indium(III) phosphate containing spirals of corner-sharing InO6 octahedra

An indium(III) phosphate, RbIn(OH)PO4, was synthesized using a high temperature, high pressure hydrothermal method and characterized by single-crystal X-ray diffraction. The compound crystallizes in the tetragonal space group P43212 (no. 96) with a= 9.400(2), c= 11.179(4)A, U= 987.8(4)A3 and Z= 8. The structure consists of spirals of cis corner-sharing InO6 octahedra running parallel to the c axis. The hydroxyl oxygen is the bridging atom. The In–O–In bonds are nearly equidistant. The composition was further defined by thermogravimetric and infrared spectroscopy measurements. Second harmonics were generated in powdered RbIn(OH)PO4 to confirm the absence of a centre of symmetry in the structure.

Cs3Ti5P7O29: a titanium(IV) phosphate containing TiO5 trigonal bipyramids

A new ternary titanium phosphate, Cs3Ti5P7O29, has been synthesized and structurally characterized by single-crystal X-ray diffraction. It crystallizes in the triclinic space group P with a= 6.307(1), b= 10.330(2), c= 20.230(3)A, α= 88.65(1), β= 84.83(1), γ= 72.37(1)°, Z= 2 and R= 0.0396. The structure consists of tunnels where the caesium cations are located. The framework is composed of two types of corner-sharing dimers of compositions Ti2O11 formed by two octahedra and Ti2O10 by an octahedron and a trigonal bipyramid, discrete TiO6 octahedra, PO4 tetrahedra and P2O7 groups. The structural formula is Cs3Ti(Ti2O)2(PO4)5(P2O7). Five-co-ordinate titanium with trigonal-bipyramidal geometry is unusual in phosphates.

CaM2(PO4)2(HPO4)(M = Fe or V): phosphates containing dimers of edge-sharing MO6 octahedra

Two new phosphates, CaM2(PO4)2(HPO4)(M = FeIII or VIII), have been synthesised hydrothermally at 400 °C and characterized by single-crystal X-ray diffraction. Crystal data: CaFe2(PO4)2(HPO4), monoclinic, space group P21/n, a= 6.3663(6), b= 19.752(2), c= 6.5030(8)A, β= 91.626(9)°, Z= 4 and R= 0.0240; CaV2(PO4)2(HPO4), as above except a= 6.359(2), b= 19.973(2), c= 6.4744(4)A, β= 91.51(1)° and R= 0.0390. The two compounds are isostructural. The framework consists of corner-sharing PO4 tetrahedra, HPO4 groups and dimers of edge-sharing MO6 octahedra forming M2O10 units. The structure of CaFe2(PO4)2(HPO4) was further defined by thermogravimetric and Mossbauer studies.