Search results for "Octahedron"
showing 10 items of 405 documents
Comparative study of the high-pressure behavior of ZnV2O6, Zn2V2O7, and Zn3V2O8
2020
We report a study of the high-pressure structural behavior of ZnV2O6, Zn2V2O2, and Zn3V2O8, which has been explored by means of synchrotron powder x-ray diffraction. We found that ZnV2O6 and Zn3V2O8 remain in the ambient-pressure structure up to 15 GPa. In contrast, in the same pressure range, Zn2V2O2 undergoes three phase transitions at 0.7, 3.0, and 10.8 GPa, respectively. Possible crystal structures for the first and second high-pressure phases are proposed. Reasons for the distinctive behavior of Zn2V2O2 are discussed. The compressibility of the different polymorphs has been determined. The response to pressure is found to be anisotropic in all the considered compounds and the room-temp…
Tuning up the Tc in Mn(II)Cu(II) bimetallic planes and design of molecular-based magnets
1998
Abstract A family of related compounds of general formula (PPh4)2Mn2[Cu((L)]3nH2O, where PPh4+ is the tetraphenylphosphonium cation and L stands for ortho-phenylenebis(oxamate) (opba, 1), ortho-phenylene (N′-methyloxamidate) (oxamate) (Meopba, 2) and ortho-phenylenebis (N′-methyloxamidate) (Me2opba, 3), have been synthesized. The X-ray absorption near-edge structure (XANES) and extended X-ray Within absorption fine structure (EXAFS) spectra at both Mn and Cu K-edges for all three compounds, as well as their powder X-ray patterns, are consistent with a layered structure built up of parallel Mn11Cu11 two-dimensional honeycomb networks separated by PPh4+ cations. Within the antonic metallic la…
Effect of cobalt doping on the local structure and dynamics of multiferroic MnWO4and Mn0.7Co0.3WO4
2013
The local atomic structure and dynamics in multiferroic MnWO4 and Mn0.7Co0.3WO4 have been studied by X-ray absorption spectroscopy at the Co(Mn) K-edge and W L3-edge. The analysis of the first coordination shell of metal ions using single-shell Gaussian approximation and regularization-like method allowed us to determine a distortion of Mn(Co)O6 and WO6 octahedra. It was found that the local environment of Co2+ ions in Mn0.7Co0.3WO4 is close to that in CoWO4, whereas the presence of cobalt ions reduces the distortion of MnO6 octahedra in comparison with pure MnWO4.
Optical absorption and Raman spectroscopy of CuWO4
2010
Th e electronic absorption and Raman spectra of CuWO4 are studied as a function of pressure in the 0 - 20 GPa range. The below-gap absorption bands at 1.15, 1.38 and 1.56 eV correspond to Cu 2+ d-transitions split by the Jahn-Teller distortion of CuO6 (Req = 1.98 A; Rax = 2.39 A; Qθ = 0.47 A). Pressure induces a strong reduction of the JT distortion up to 10 GPa. Above this pressure we observe, by optical absorption and Raman spectroscopy, a first-order phase transition at 11 GPa with phase coexistence in the 10-12 GPa range, as it is confirmed by Raman spectroscopy. The absorption spectra suggest that two different Cu 2+ sites are formed in the high pressure phase, each having rather diffe…
Synthesis and characterization of a new layered organic-inorganic hybrid nickel(II) 1,4 : 5,8-naphthalenediimide bis-phosphonate, exhibiting canted a…
2008
A new Ni(II) layered hybrid organic-inorganic compound of formula Ni{sub 2}[(NDI-BP)(H{sub 2}O){sub 2}].2H{sub 2}O has been prepared in very mild conditions from N,N'-bis(2-phosphonoethyl)napthalene-1,4:5,8-tetracarboximide (NDI-BP ligand) and NiCl{sub 2}. The X-ray powder structure characterization of the title compound suggests a pillared layered organic-inorganic hybrid structure. The distance between the organic and inorganic layers has been found to be 17.8 A. The inorganic layers consist of corner sharing [NiO{sub 5}(H{sub 2}O)] octahedra and they are pillared by the diphosphonate groups. DC and AC magnetic measurements as a function of temperature and field indicate the presence of 2…
Hydrogen-bonded 2-(2-pyridyl)imidazole (pyim) manganese(II) complexes as building blocks for molecular assembling: Syntheses and structural character…
2008
Abstract The preparation and crystal structures of three new manganese(II) complexes with 2-(2-pyridyl)imidazole (pyim) and pseudohalides as ligands, cis-[Mn(pyim)2(N3)2] (1), cis-[Mn(pyim)2(NCO)2] (2) and cis-[Mn(pyim)2(NCS)2] (3), are reported. The structural building block in each structure is a mononuclear, neutral complex unit. The metal ion in each case adopts a distorted octahedral coordination geometry with the two pseudohalide ligands in cis positions. The main differences between the molecular structures of the three compounds are associated with the orientation of the anionic ligands. Hydrogen bonds between imidazole N–H and the metal-coordinated nitrogen atom of the pseudohalide…
1,2,4,5‐Benzenetetracarboxylic Acid and 4,4′‐Bipyridine as Ligands in Designing Low‐Dimensional Coordination Polymers
2004
The combined use of 1,2,4,5-benzenetetracarboxylic acid (H4bta) and 4,4′-bipyridine (bpy) as ligands with MnII and CoII ions afforded two polymeric compounds with the formulae [Mn(Hbta)(Hbpy)(H2O)2] (1) and [H2bpy][Co(bta)(bpy)(H2O)2] (2). 1 and 2 were prepared under hydrothermal conditions (145 °C, 3 h) and characterized by elemental analysis, IR spectroscopy, TG-DTA analysis and single-crystal X-ray diffraction methods. 1 exhibits a novel double chain structure growing along the b axis where the manganese atoms are linked by tris-monodentate Hbta3− ligands. The values of the manganese···manganese intrachain separations are 7.627(2) A [Mn(1)···Mn(1c); c = −x + 1/2, y − 1/2, −z] and 9.274(4…
[(1,4,8,11-Tetraazacyclotetradeca-1,4,8,11-tetrayl)tetraacetamide-kappa6N1,N4,N8,N11,O1,O8]copper(II) sulfate 4.5-hydrate.
2002
The crystal structure of the title copper(II) complex, [Cu(C(18)H(36)N(8)O(4))]SO(4).4.5H(2)O, formed with the tetraamide cyclam derivative 2-(4,8,11-triscarbamoylmethyl-1,4,8,11-tetraazacyclotetradec-1-yl)acetamide (TETAM), is described. The macrocycle lies on an inversion centre occupied by the hexacoordinated Cu atom. The four macrocyclic tertiary amines form the equatorial plane of an axially Jahn-Teller elongated octahedron. Two O atoms belonging to two diagonally opposite amide groups occupy the apical positions, giving rise to a trans-III stereochemistry, while both the remaining pendant side arms extend outwards from the macrocyclic cavity and are engaged in hydrogen bonds with sulf…
Synthesis, structural and spectroscopic characterization of the α,ω-diammonioalkane hexabromorhodates(III) [H3N(CH2)xNH3]2[H 5O2][RhBr6]Br2 (x = 3, 4…
2002
The reaction of rhodium(III) chloride trihydrate with 1,3-diaminopropane and 1,4-diaminobutane in concentrated hydrobromic acid results in the formation of the bis(α,ω-diammonioalkane) diaquahydrogen(1+) hexabromorhodate(III) dibromides [H3N(CH2)xNH3]2[H5O2][RhBr6]Br2 (x = 3, 4). Dark red single crystals were obtained by diffusion-controlled crystallization at room temperature. Both compounds crystallize in space group type P1̄ and their structures are closely related. In view of crystal engineering they are inorganic-organic hybrid materials built up from octahedral [RhBr6]3−, simple Br− and flexible chain-like [H3N(CH2)xNH3]2+ ions with the [H5O2]+ and further Br− ions incorporated and th…
Synthesis, structure and magnetic properties of Mn(II) and Cu(II) complexes with the dicyano-acetic acid methyl ester anion
2001
The preparation of the sodium salt of dicyano-acetic acid methyl ester (NaCH 3 OC(O)C(CN) 2 ) (NaL) is reported. The structure of this anion is related to the structure of the dicyanamide, whose chelating capability has been used to develop 2D networks. Two new complexes of formula [M(L) 2 (H 2 O) 2 ] (M=Mn 2+ ( 1 ) and Cu 2+ ( 2 )) have been synthesized and their crystal structures determined by single-crystal X-ray diffraction. The coordination geometry of Mn atom in 1 is approximately octahedral, and the Mn atoms are μ 2 -bridged by two pairs of L − resulting in an infinite one-dimensional chain. Two types of hydrogen bonds link the chains within a 3-dimensional infinite lattice. The coo…