8 research outputs found
Different complexation behaviour of a proton transfer compound obtained from pyridine-2,6-dicarboxylic acid and creatine with Tl(I), Cu(II), Fe(III), and Bi(III): synthesis, characterization, crystal structures and solution studies
No full textThe dif fer ent complexation meth ods of a pro ton trans fer com pound,
(creatH)(pydcH)·H2O (pydcH2 = pyridine-2,6-di car box yl ic acid; creat = creatinine) with
metal ions have been stud ied and for ma tion of [(Tl(pydcH)]n (1) ,
[(Fe(pydc)(H2O)2)2ox]·6H2O (2), [Cu(pydc)(pydcH2)]·2H2O (3) and
(creatH)2[Bi(pydc)2]2·4H2O (4) are re ported. The char ac ter iza tion was per formed us ing
IR spec tros copy and sin gle crys tal X-ray dif frac tion anal y sis. The Tl(I) com plex
[(Tl(pydcH)]n (1) ob tained from (creatH)(pydcH)·H2O is a poly meric sys tem, show ing
only the con tri bu tion of the an ionic spe cies of (creatH)(pydcH)·H2O to the
complexation. The Fe(III) and the Cu(II) com plexes [(Fe(pydc)(H2O)2)2ox]·6H2O (2)
(ox = ox a late) and [Cu(pydc)(pydcH2)]·2H2O (3) were also ob tained from
(creatH)(pydcH)·H2O. The Bi(III) com plex (creatH)2[Bi(pydc)2]2·4H2O (4) is a dimeric
sys tem, show ing both con tri bu tion of the cationic and an ionic frag ments. The com plexes
1–4 show a va ri ety of struc tural fea tures in clud ing mononuclear, binuclear, poly meric
struc tures and un usual ligand for ma tion. In com pounds (1), (2), (3) and (4), a large num -
ber of hy dro gen bonds are ob served. These in ter ac tions as well as p-p stack ing play an
im por tant role in the for ma tion and sta bi li za tion of supra mo lecu lar sys tems in the crys tal
lat tices. The stoichiometry and sta bil ity of the Cu(II), Tl(I) and Bi(III) com plexes with
(pydc)(creat) and Fe(III) with pydc-ox mix ture in aque ous so lu tion were in ves ti gated by
potentiometric pH ti tra tion
Pyridine-2,6-bis(monothiocarboxylic) acid and 2-aminopyridine as building blocks of a novel proton transfer compound: Solution and X-ray crystal structural studies
No full textThe synthesis of a novel proton transfer compound (2-apyH)(pdtcH), L, derived from pyridine-2,6-bis(monothiocarboxylic) acid, (pdtcH2), is reported. This compound was prepared from the reaction between pdtcH2, and 2-aminopyridine, (2-apy), in water as solvent. The characterization was performed using 1H and 13C solution NMR and single crystal X-ray diffraction analysis. Crystal structure analysis reveals that intra- and intermolecular proton transfer from the diacid pdtcH2 to the base 2-apy results in the formation of a supramolecular network, which is self-assembled via non-covalent interactions. The monocationic (2-apyH)+ and monoanionic (pdtcH)− building blocks are connected through H-bonding, π-π interactions and ion-pairing simultaneously as shown in the X-ray crystal structure. The monoanionic fragments are located almost parallel to each other and the cationic species have also situations nearly parallel to each other, positioning almost perpendicular to anions. The aqueous solution studies were accomplished by spectrophotometric and potentiometric pH titrations. The most abundant proton transfer species present at pH < 6 is (2-apyH)(pdtcH), in support of association between (2-apyH)+ and (pdtcH)−in L, being similar to that observed by NMR spectroscopy and X-ray crystal structure analysis
Synthesis, Crystal Structure, and Magnetic Properties of Li<sub>3</sub>Mg<sub>2</sub>OsO<sub>6</sub>, a Geometrically Frustrated Osmium(V) Oxide with an Ordered Rock Salt Structure: Comparison with Isostructural Li<sub>3</sub>Mg<sub>2</sub>RuO<sub>6</sub>
No full textThe novel osmium-based oxide Li3Mg2OsO6 was synthesized in polycrystalline form by reducing
Li5OsO6 by osmium metal and osmium(IV) oxide
in the
presence of stoichiometric amounts of magnesium oxide. The crystal
structure was refined using powder X-ray diffraction data in the orthorhombic Fddd space group with a = 5.88982(5) Å, b = 8.46873(6) Å, and c = 17.6825(2)
Å. This compound is isostructural and isoelectronic with the
ruthenium-based system Li3Mg2RuO6. The magnetic ion sublattice Os5+ (S = 3/2) consists of chains of interconnected
corner- and edge-shared triangles, which brings about the potential
for geometric magnetic frustration. The Curie–Weiss law holds
over the range 80–300 K with C = 1.42(3) emu·K/mol
[μeff = 3.37(2) μB] and θC = −105.8(2) K. Below 80 K, there are three anomalies
at 75, 30, and 8 K. Those at 75 and 30 K are suggestive of short-range
antiferromagnetic correlations, while that at 8 K is a somewhat sharper
maximum showing a zero-field-cooled/field-cooled divergence suggestive
of perhaps spin freezing. The absence of magnetic Bragg peaks at 3.9
K in the neutron diffraction pattern supports this characterization,
as does the absence of a sharp peak in the heat capacity, which instead
shows only a very broad maximum at ∼12 K. A frustration index
of f = 106/8 = 13 indicates a high degree of frustration.
The magnetic properties of the osmium phase differ markedly from those
of the isostructural ruthenium material, which shows long-range antiferromagnetic
order below 17 K, f = 6, and no unusual features
at higher temperatures. Estimates of the magnetic exchange interactions
at the level of spin-dimer analysis for both the ruthenium and osmium
materials support a more frustrated picture for the latter. Errors
in the calculation and assignment of the exchange pathways in the
previous report on Li3Mg2RuO6 are
identified and corrected
A search for disorder in the spin glass double perovskites Sr<sub>2</sub>CaReO<sub>6</sub>and Sr<sub>2</sub>MgReO<sub>6</sub>using neutron diffraction and neutron pair distribution function analysis
No full textCarbon formation on stainless steel 304H in convection section of ethane cracking plant
No full textThe coking of stainless steel 304H alloy (SS304H) has been investigated in ethane-steam mixtures in the presence/absence of a few ppm of H2S at 700°C. In this, first detailed study of the influence of H2S on carbon morphology on SS304H, we show that the addition of H2S greatly altered the carbon morphology, in the long-term experiments (90 h). For shorter exposure times (4 h), carbon formation decreased as H2S concentration was increased. This improved carbon tolerance of SS304H is likely due to adsorption of sulphfur on its surface. Addition of H2S did not change the ethane cracking initiation temperature or the product distribution.</p
Intralayer Cation Ordering in a Brownmillerite Superstructure: Synthesis, Crystal, and Magnetic Structures of Ca<sub>2</sub>FeCoO<sub>5</sub>
No full textChemInform Abstract: Intralayer Cation Ordering in a Brownmillerite Superstructure: Synthesis, Crystal, and Magnetic Structures of Ca2FeCoO5.
No full textIntralayer Cation Ordering in a Brownmillerite Superstructure: Synthesis, Crystal, and Magnetic Structures of Ca<sub>2</sub>FeCoO<sub>5</sub>
No full textThe synthesis, crystal, and magnetic structures and the bulk magnetic properties of Ca2FeCoO5, a brownmillerite type oxide, are presented. The crystal structure, solved and refined from single crystal X-ray and powder neutron diffraction data, is described in Pbcm with cell parameters, a = 5.3652(3) Å, b = 11.0995(5) Å, c = 14.7982(7) Å. Thus, one axis, b in this setting, is doubled in comparison with the standard brownmillerite structure description giving rise to two sets of octahedral and tetrahedral sites. Aided by the strong scattering contrast between Fe and Co for neutrons, a nearly perfect intralayer cation site ordering, not observed for any brownmillerite before, is detected in the tetrahedral layers. There is a lesser degree of cation site ordering in the octahedral sites. Overall, the Fe/Co site ordering is of the NaCl type both within and between the tetrahedral and octahedral layers. There are also both intra- and interlayer ordering of tetrahedral chain orientations. The left- and right-handed orientations alternate within each tetrahedral layer as well as between the closest tetrahedral layers. The occurrence of the rare Pbcm space group in Ca2FeCoO5 is not consistent with a recently proposed structure-field map for brownmillerite oxides. The magnetic structure is G-type antiferromagnetic, with preferred orientation of magnetic moments parallel to the longest axis between 3.8 K to 100 K which switches to the shortest axis between 225 K and 550 K. The neutron diffraction data indicate different site specific ordering temperatures at about 450(5) K and 555(5) K. The refined ordered moments at 3.8 K are somewhat smaller than expected for Fe3+ and Co3+(high spin) but are similar to those found in Sr2FeCoO5. There is evidence for spin canting from isothermal magnetization data that shows well pronounced hystereses and remnant magnetizations at 5 K and 200 K
