Internal Structure and Magnetic Properties in Cobalt Ferrite Nanoparticles: Influence of the Synthesis Method

The design of novel nanostructured magnetic materials requires a good understanding of the variation in the magnetic properties due to different synthesis conditions. In this work, four different procedures for fabricating Co‐ferrite nanoparticles with similar sizes between 7 and 10 nm are compared by studying their structural and magnetic properties. Non‐aqueous methods based on the thermal decomposition of metal acetylacetonates at high temperatures, either with or without surfactants, provide highly crystalline nanoparticles with large saturation magnetization values and a coherent reversal of the magnetic moment. However, variations in the density of defects and in the shape of the nanocrystals determine the distribution of switching fields and the effective magnetic anisotropy, which reaches up to ≈1 × 10⁷ erg cm^?3 for oleic acid‐capped 9 nm nanoparticles. It is shown that the saturation magnetization values for nanoparticles produced by different methods are in the range between 49 and 95 emu g^?1 due to differences in the stoichiometry, in the cation occupancy, in the magnetic disorder and in the spin canting of the magnetic sub‐lattices, the latter evaluated by in‐field Mössbauer spectroscopy.     

Lacunar Keggin Heteropolyacid Salts: Soluble,Solid and Solid-Supported Catalysts

Polyoxometalates are an important class of environmentally friendly catalysts. The Keggin heteropolyacids containing tungsten or molybdenum addenda atoms have received great attention because they have attractive acid and redox properties, which may be easily tunable through changes in their composition and structure. The replacement of their protons by large radium cations makes insoluble the Keggin heteropolyacids and increases their surface area. On the other hand, the removal of tungsten or molybdenum atoms from the Keggin heteropolyanion generates vacancies, which can activate different organic substrates. Therefore, solid lacunar heteropolyacid salts are potentially active catalysts and selective in a plethora of reactions. These catalysts are used either in homo- or heterogeneous conditions. In this review, we wish would highlight recent advances achieved in the chemistry of lacunar Keggin heteropolyacids. We describe their use as solid, soluble or solid-supported catalysts in reactions of oxidation of alcohols and olefins, oxidative desulfurization and acid-catalyzed reactions such as acetalization, esterification, and transesterification.     

Integration Operators in Average Radial Integrability Spaces of Analytic Functions

Mediterranean Journal of Mathematics - The original article has been published inadvertently with errors in page number 2.     

Polyol-assisted coprecipitation synthesis of BiOI photocatalyst and its activity to remove NOx

Research on Chemical Intermediates - BiOI samples were synthesized by coprecipitation method in glycerol medium at 100 °C followed by a thermal treatment of the precursor powders at...     

Aminodiphenylphosphanes: Isotope‐induced chemical shifts 1Δ14/15N(31P), coupling constants 1J(31P,15N), and chemical shifts δ15N and δ31P

A series of aminodiphenylphosphanes 1 [Ph₂P‐N(H)tBu ( a ), ‐NEt₂ ( b ), ‐NiPr₂ ( c )], 2 [Ph₂P‐NHPh ( a ), ‐NH‐2‐pyridine ( b ), ‐NH‐3‐pyridine ( c ), ‐NH‐4‐pyridine ( d ), NH‐pyrimidine ( e ), NH‐2,6‐Me₂‐C₆H₃ ( f ), NH‐3‐Me‐2‐pyridine ( g )], 3 [Ph₂P‐N(Me)Ph ( a ), ‐NPh₂ ( b )], and N‐pyrrolyldiphenylphosphane 4 (Ph₂P‐NC₄H₄) was prepared and studied by NMR (¹H, ¹³C, ³¹P, ¹⁵N NMR) spectroscopy. The isotope‐induced chemical shifts ¹Δ^14/15N(³¹P) were determined at natural abundance of ¹⁵N by using HEED INEPT experiments. A dependence of ¹Δ^14/15N(³¹P) on the substituents at nitrogen was found (alkyl < H < aryl; increasingly negative values). The magnitude and sign of the coupling constants ¹J(³¹P,¹⁵N) (positive sign) are dominated by the presence of the lone pair of electrons at the phosphorus atom. The X‐ray structural analysis of 2b is reported, showing the presence of dimers owing to intermolecular hydrogen bridges in the solid state. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:542–550, 2001     

Synthesis of Phosphanes Bearing 2‐Imino‐1,3‐thiazolidine Ligands – X‐Ray Analyses and NMR Spectroscopy

Pseudo‐ephedrine derived 2‐imino‐1,3‐thiazolidine 1 reacts with tris(diethylamino)phosphane by stepwise replacement of the diethylamino group to give the mono‐, bis‐ and tris(imino)phosphanes 2 , 3 and 4 , respectively, of which 4 could be isolated in pure state. The analogous reaction with diethylamino‐diphenylphosphane affords the imino‐diphenylphosphane 5 . The iminophosphanes react with sulfur or selenium to give the corresponding phosphorus(V) compounds. In contrast, the reaction of the iminophosphanes with oxygen is very slow; anhydrous trimethylamine N‐oxide reacts in the melt with the phosphanes to give the oxides 4(O) and 5(O) . The molecular structures of 4(O) (in mixture with 4 ), 4(Se) , 5(S) and 5(Se) were determined by X‐ray analysis. In all cases the ring‐sulfur and the phosphorus atoms are in cis‐positions at the C=N bonds. The analogous solution structures were determined by ¹H, ¹³C, ¹⁵N, ³¹P and ⁷⁷Se NMR spectroscopy. In the case of the compounds 5 , 5(O) , 5(S) and 5(Se) the isotope‐induced chemical shifts ¹δ^14/15N(³¹P) were determined, using INEPT‐HEED experiments.     

Implementation of atomic basis set composed of 1s Gaussian and 1s Slater-type orbitals to carry out quantum mechanics molecular calculations

A mixed atomic basis set formed with ls Slater-type orbitals and 1s floating spherical Gaussian orbitals is implemented. Evaluation of multicenter integrals is carried out using a method based on expansion of binary products of atomic basis functions in terms of a complete basis set, and a systematic analysis is performed. The proposed algorithm is very stable and furnishes fairly good results for total energy and geometry. An LCAO-SCF test calculation is carried out on LiH. The trends observed show that there are some combinations of mixed orbitals that are appropriate to describe the system. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 604–609, 1999     

Versatile behavior of 2-guanidinobenzimidazole nitrogen atoms toward protonation,coordination and methylation

The structure, dynamic behavior, protonation, methylation, and coordination sites of 2-guanidinobenzimidazole 1a were investigated. Structures of compounds [2-guanidinium-1,3,10-trihydrobenzimidazole]sulfate 1b , [2-guanidinium-1,3-dihydro-benzimidazole]sulfate 1c–1d , [2-guanidinium-1,3-dihydro-benzimidazole]tetrafluoroborate 1e , [2-guanidinium-1,3-dihydro-benzimidazole]chloride 1f , [2-guanidinium-1,3-dihydro-benzimidazole] perchlorate 1g , 2-guanidino-1-methyl-benzimidazole 2a , [2-guanidinium-1,3-dimethyl-benzimidazole]iodide 2b , [2-guanidinium-1-methyl-3-hydro-benzimidazole]chloride 2c , [2-guanidinium-1,10-dihydro-benzimidazole]acetate 3 , 2-guanidino-1-hydro-3-borane-benzimidazole 4a , 2-guanidino-1-methyl-3-borane-benzimidazole 4b , (2-guanidino-benzimidazole)dimethyltin 5 , [bis(2-guanidino-10-hydro-benzimidazole)nickel(II)] 6 , and [bis(2-guanidino-1,10-dihydro-benzimidazole)zinc(II)]nitrate 7 were determined based on ¹H, ¹³C, and ¹⁵N NMR spectroscopy. The X-ray diffraction structures of 2a, 2b, 3, 6 , and 7 were obtained. The results show that 1a has an open structure without an intramolecular hydrogen bond in DMSO or DMF. The imidazolic N-3 is the preferred basic site in solution for protonation, methylation, and coordination and not N-10 as was suggested from semiempirical calculations. Under strong acidic conditions, diprotonation occurs at N-3 and N-10. In the solid state, 3 and 6 were protonated preferently at N10 rather than at N-1. © 1997 John Wiley & Sons, Inc. Heteroatom Chem 8: 397–410, 1997