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.     

Stereoselective addition of dimethyl thiophosphite to imines

Dimethyl thiophosphite (DMTP) was synthesized from dimethyl phosphite, and the diastereoselective addition of DMTP to benzaldimines bearing chiral auxiliary groups was examined. Yields of the product alpha-aminophosphonothionates ranged from 17% to 75% after chromatography. The addition of DMTP to the benzaldimine derived from (S)-phenylglycinol afforded the highest diastereoselectivity (83:17), whereas addition of DMTP to the benzaldimine derived from threonine methyl ester and alanine methyl ester were far less diastereoselective, affording 38:62 and 61:39 ratios, respectively. Addition of DMTP to the benzaldimine derived from (R)-alpha-methylbenzylamine (78:22) and (S)-serine methyl ester (73:27) were intermediate in selectivity. DMTP addition to the imines formed between serine methyl ester and acetaldehyde and isobutyraldehyde gave 55:45 and 70:30 ratios, respectively, with the diastereoselectivity corresponding roughly to the size of the alpha-alkyl group. The stereochemistry of the newly formed alpha-stereocenters resulting from the addition of DMTP to (S)- and (R)-phenylglycinol benzaldimines was confirmed by conversion of the product alpha-aminophosphonothionates to the known enantiomers of phosphonophenylglycine.     

Three-dimensional synchronous fluorescence spectrometry for the analysis of three-component alkaloid mixtures

A study of a simple and sensitive method for the determination of berberine, luguine and sanguinarine in mixtures by normal and synchronous derivative spectrofluorimetry is described. The influence of solvents and other experimental variables is discussed. A three-dimensional plot of both emission-excitation and synchronous spectra obtained by a new software program provides additional information for optimizing instrumental parameters. Linear, normal and derivative calibration graphs are established in the ng/ml range. A statistical analysis of the results and their application to synthetic and natural samples is given.     

A new polymorph of bis[2,6‐bis(1H‐benzimidazol‐2‐yl‐κN3)pyridinido‐κN]zinc(II)

The title compound, [Zn(C₁₉H₁₂N₅)₂], crystallizes in the tetragonal space group P4₃2₁2, with the monomer residing on a twofold axis. The imidazole N‐bound H atoms are disordered over the two positions, with refined occupancies of 0.59 (3) and 0.41 (3). The strong similarities to, and slight differences from, a reported P4₂2₁2 polymorph which has a 50% smaller unit‐cell volume [Harvey, Baggio, Muñoz & Baggio (2003). Acta Cryst. C 59 , m283–m285], to which the present structure bears a group–subgroup relationship, are discussed.     

Eco-friendly reductive acetamidation of arylnitro compounds by thioacetate anion through in situ catalytic regeneration: application in the synthesis of Acetaminophen™

A novel one-step reductive acetamidation of arylnitro compounds mediated by thioacetate anion in thioacetic acid via in situ catalytic regeneration was developed and applied to an efficient synthesis of Acetaminophen™.     

Effects of the Water Quantity on the Solventless TEOS Hydrolysis Under Ultrasound Stimulation

The acid hydrolysis under ultrasound stimulation of solventless tetraethoxysilane(TEOS)-water mixtures was studied at 40°C, by means of a heat flux calorimetric method, as a function of the initial water/TEOS molar ratio (r) ranging from 2 to 10. The method is based on the time record of the exothermic heat peak of hydrolysis, arising after an induction time under ultrasound stimulation, which is a measure of the reaction rate. The hydrolysed quantity was found to be approximately independent of the water/TEOS molar ratio, even for r < 4. Polycondensation reaction takes place mainly for low water/TEOS molar ratio in order to supply water to allow almost complete hydrolysis. The overall process of dissolution and hydrolysis has reasonably been described by a previous modelling. The dissolution process of water in TEOS, under ultrasound stimulation and acid conditions, was found to be rather dependent of the alcohol produced in the hydrolysis reaction instead of the initial water quantity present in the mixture.     

A monoclinic form of dendocarbin A: a borderline case of one‐dimensional isostructural polymorphism

The title compound, dendocarbin A [systematic name: (1R,5aS,9aS,9bR)‐1‐hydroxy‐6,6,9a‐trimethyldodecahydronaphtho[1,2‐c]furan‐3‐one], C₁₅H₂₂O₃, is a sesquiterpene lactone isolated from Drimys winteri var chilensis. The monoclinic phase described herein displays an identical molecular structure to the orthorhombic phase that we reported previously [Paz Robles et al. (2014). Acta Cryst. C 70 , 1007–1010], while varying significantly in chain pitch, and can thus be considered as a borderline case of one‐dimensional isostructural polymorphism.     

Fractal character of the SAXS correlation volume in poly(ethylene glycol)/silica hybrid wet gels

Small-angle X-ray scattering (SAXS) was employed to study the nanostructural properties of poly(ethylene glycol)(PEG)/silica hybrid wet gels prepared from hydrolysis of tetraethoxysilane (TEOS) in mixtures with PEG/(PEG + TEOS) molar ratio in the nominal range between 0 and 0.8. The SAXS pattern was found to be well fitted by the scattering from a polymeric particle of radius of gyration R _g with an internal structure of primary silica particles described by a polymeric constraint of a mass-fractal of dimension D. R _g increases with the PEG quantity while D first increases from 2.24 for the pure TEOS-derived gel to reach values between 2.46 and 2.40 with the additions of PEG. The correlation volume V _c as determined by SAXS for such a polymeric structure behaves as a volume-fractal and accordingly scales with R _g as V _c ~ R _g ^D . An overall mean value of about 1 nm could be estimated as an upper limit for the radius of the primary silica particle building up the structure of all the wet gels, independent of the PEG addition.