Experimental evidence and DFT studies of next-nearest-neighbor magnetic interactions through diamagnetic 3d and 4d ions

The copper template effect allows the preparation of tridentate ligands that chelate copper ions, leaving unoccupied the fourth basal coordination position and at least one axial position of the copper coordination polyhedron. Two such cationic complexes, [LCu](+) and [L(1)Cu](+) (L(-) = 2-{(E)-[(2-aminoethyl)imino]methyl}phenoxo] and L(1-) = 2-{(E)-[(2-aminopropyl)imino]methyl}phenoxo), react with diamagnetic polycyanometalate tectons such as Ni(CN)(4)(2-) or Ag(CN)(2)(-) to yield different neutral 1D complexes. In {[(LCu)(2)Ni(CN)(4)]}(n) (1) the four cyano nitrogen atoms are involved in coordination with copper ions in such a manner that each copper atom is pentacoordinated and linked to two cyano functions that occupy axial and equatorial coordination positions. Two L(1)Cu(+) cationic entities are linked, through their equatorial plane, to two trans cyano groups of the Ni(CN)(4)(2-) tecton in complex [(L(1)Cu)(2)Ni(CN)(4)] (2), the two uncoordinated cyano groups being involved in hydrogen bonds. 2 is a racemate, a S stereoisomer being associated with a R one in each [(L(1)Cu)(2)Ni(CN)(4)] unit. Zigzag Cu-Ag chains are present in [(LCu)Ag(CN)(2)] (3), where the copper centers are pentacoordinated and connected to the cyano groups in an alternate axial-equatorial coordination scheme. A bidimensional structure is developed by interchain argentophilic interactions. In complex 4, {(L(1)CuMeOH)(L(1)Cu)[Ag(CN)(2)](2)}, two L(1)Cu units are connected by a NC-Ag-CN bridge in an equatorial position. These resulting units exhibit argentophilic interactions with [Ag(CN(2))](-) entities that are monocoordinated in the equatorial position to the next unit, ultimately leading to a chain. Weak Cu-Cu magnetic interactions are detected in the four compounds, antiferromagnetic in the case of equatorial-equatorial copper interactions, ferromagnetic for orthogonal interacting copper orbitals (axial-equatorial interactions), while axial-axial bridges are characterized by an absence of interaction. The presence of weak ferromagnetic interactions through large NC-Ni-CN or NC-Ag-CN bridges (Cu···Cu distances larger than 10 ?) furnishes experimental evidence for the existence of next-nearest-neighbor interactions through diamagnetic centers. DFT calculations do confirm the existence of these magnetic transmission pathways through the diamagnetic metal bridge.     

Geometry and the Jones projection of a state

LetA be a von Neumann algebra and a faithful normal state. ThenO = { ºAd(g ¹) :g G _A }andU = { ºAd(u ^*) :u U _A are homogeneous reductive spaces. IfA is aC ^* algebra,e the Jones projection of the faithful state viewed as a conditional expectation, then we prove that the similarity orbit ofe by invertible elements ofA can be imbedded inAA in such a way thate is carried to 1 1 and the orbit ofe to a homogeneous reductive space and an analytic submanifold ofAA.     

Structure functions in nuclei: Quark clusters and size effects

Two of the most interesting ideas to explain the EMC effect, clusters of quarks and confinement size factors, are unable to fully explain the existing data. In this paper we argue that the existence of clusters with different numbers of quarks are in the origin of different size parameters controlling the lowQ ² limit in the QCD evolution and thus we combine the two ideas. As a result we obtain a model for structure functions with two basic effective parameters: the average numberi of nucleons per cluster and the corresponding size parameterR _i . We achieve good agreement with the existing data for a wide range ofQ ²(?2 GeV²) and for all values ofx. Simple parametrizations of the Sea, Gluon and Valence distributions, for pion, nucleon and nuclei, are given. Some applications of the model, in particular to Drell-Yan processes, are discussed.     

Photoluminescent property of mechanically milled BaWO4 powder

Crystalline BaWO₄ (BWO) powder obtained by the polymeric precursor method was structurally disordered by means of high-energy mechanical milling. For the first time a strong and broad photoluminescence (PL) has been measured at room temperature for mechanically milled BWO powder and interpreted by ground-state quantum mechanical calculations in the density functional theory framework. Two periodic models have been studied; one representing the crystalline form and the other one representing the disordered BWO powder. These models allowed the calculation of electronic properties, which are consistent with the experimental results, showing that structural disorder in the lattice is an important condition to generate an intense and broad PL band.     

Tris(2,4,6-trichloro-3,5-dinitrophenyl)methyl radical: a new stable coloured magnetic species as a chemosensor for natural polyphenols

We report the synthesis, electron paramagnetic resonance and electrochemical properties of a novel stable radical of the TTM series. Its strong electron acceptor ability has been tested with (-)-epicatechin, a natural polyphenolic antioxidant.     

Transition from the layered Sr2RhO4 to the monodimensional Sr4RhO6 phase

Study of the structural changes occurring during the reduction process of the Sr2RhO4+delta, (214), n=1 term of the Ruddlesden and Popper series, shows that for delta <0.02 values, this material dissociates into the Sr4RhO6 (416) monodimensional phase, alpha = infinity, beta = 0 compound of the (A3B2O6)alpha-(A3B3O9)beta family, and Rh metal. During the first stage, this process occurs by the formation of an intergrowth between the (214) and (416) materials which can be only detected by high resolution electron microscopy and is easily interpreted on the basis of the structural relationship established between them. Further reduction allows the segregation of both phases as separated entities, which coexist with Rh metal. The dissociation process is reversible and, under oxidizing conditions, a layered material with anionic composition delta =0.06 is always obtained. This behaviour seems to be a general way of accommodating the compositional changes in layered A2BO4 phases where the B cation is always in a octahedral environment. The structural mechanism of this transformation is proposed, and the structural relationship between these two low-dimensional oxides is established.     

Gold Extracted from Wastewater as an Efficient MOF-Supported Electrocatalyst

The recovery of gold from wastewater is necessary from both environmental and economic standpoints. Metal–organic frameworks (MOFs) can serve as high-capacity and selective adsorbents, as shown in a recent work by Zhao and co-workers. Their novel three-dimension cationic framework goes further than selectively adsorbing AuCl₄⁻. It also serves as a stable platform to transform adsorbed gold into an efficient catalyst for the electrochemical reduction of CO₂. This work highlights the versatility of MOFs, which can serve as selective adsorbents and as a support for nanoparticle catalysts.     

New structural features in triphenylphosphinesilver(I) sulfanylcarboxylates

We investigated the reactions of 1.5 : 1 : 1 mole ratio mixtures of triphenylphosphine, silver nitrate and 3-(aryl)-2-sulfanylpropenoic acids H(2)xspa in chloroform/water, where in the acid nomenclature, spa = 2-sulfanylpropenoato and x = p, Clp, mp, diBr-o-hp or f with p = 3-phenyl-, Clp = 3-(2-chlorophenyl)-, mp = 3-methoxyphenyl-, diBr-o-hp = 3-(3,5-dibromo-2-hydroxyphenyl)- and f = 3-(2-furyl)-. The compounds [Ag(PPh(3))(Hpspa)](1), [(AgPPh3)2(xspa)][x = Clp (2), o-mp (3), p-mp (4), diBr-o-hp (5) and f (6)] and [Ag(PPh3)3(Hfspa)](7) were isolated and all except 7 were characterized by IR, Raman and FAB mass spectrometry and by 1H, 13C and 31P NMR spectroscopy. Compound 6 was also characterized by (13)C CP/MAS, and compounds 1 and 6 by (109)Ag NMR spectroscopy. The crystal structures of 1, 2, 3, 4.(CH3)2CO, 5, 6.(CH3)2CO and 7 were determined by X-ray diffraction. has a supramolecular structure based on hydrogen bonding between dinuclear units, and all the other complexes adopt discrete structures. 2, 3, 4.(CH3)2CO, 5, and 6.(CH3)2CO are tetranuclear, and 7 mononuclear. The tetranuclear complexes contain the eight-membered coordination ring Ag4S2O2 (2, 3, 4.(CH3)2CO, 6.(CH3)2CO) or the twelve-membered ring Ag4(CO2)2S2 (5).     

Methylmercury and dimethylthallium complexes of 5-(4′-dimethylaminobenzylidene)-2-thiohydantoin (HDABTd): The crystal and molecular structures of HDABTd and [TlMe2(DABTd)(DMSO)]

The ligand 5-(4′-dimethylaminobenzylidene)-2-thiohydantoin (HDABTd) was prepared and its structure determined by X-ray diffraction. In the crystal, ligand molecules are linked in chains along the [110] direction by intermolecular N(3)–H(3)O(1)^I and N(1)–H(1)Sⁱⁱ hydrogen bonds. The complexes [HgMe(DABTd)] and [TlMe₂(DABTd)] were prepared by reaction of the ligand with methylmercury acetate or dimethylthallium hydroxide, and were characterized in the solid state by IR spectroscopy and in solution by conductivity measurements and ¹H, ¹³C, ¹⁹⁹Hg and ²⁰⁵Tl NMR spectroscopy. The dimethylthallium complex crystallized in DMSO solution as [TlMe₂(DABTd)(DMSO)], an X-ray diffraction study of which showed its thallium atoms to be coordinated to the two methyl C atoms, the oxygen atom of a DMSO molecule, the S and N(1) atoms of one DABTd ligand and, more weakly, to the oxygen atom of a neighbouring DABTd. This last interaction links the molecules of the complex in chains parallel to the b axis. Crystals of the methylmercury(II) complex contain three [HgMe(DABTd)]·DMSO structures per asymmetric unit, but poor data quality prevented complete refinement.