Magnetic exchange interactions and magneto-structural correlations in heterobridged μ-phenoxo-μ(1,1)-azide dinickel(II) compounds: a combined experimental and theoretical exploration

This investigation presents the syntheses, crystal structures, magnetic properties, and density functional theoretical modeling of magnetic behavior of two heterobridged μ-phenoxo-μ(1,1)-azido dinickel(II) compounds [Ni(II)(2)(L(1))(2)(μ(1,1)-N(3))(N(3))(H(2)O)]·CH(3)CH(2)OH (1) and [Ni(II)(2)(L(2))(2)(μ(1,1)-N(3))(CH(3)CN)(H(2)O)](ClO(4))·H(2)O·CH(3)CN (2), where HL(1) and HL(2) are the [1+1] condensation products of 3-methoxysalicylaldehyde and 1-(2-aminoethyl)-piperidine (for HL(1))/4-(2-aminoethyl)-morpholine (for HL(2)), along with density functional theoretical magneto-structural correlations of μ-phenoxo-μ(1,1)-azido dinickel(II) systems. Compounds 1 and 2 crystallize in orthorhombic (space group Pbca) and monoclinic (space group P2(1)/c) systems, respectively. The coordination environments of both metal centers are distorted octahedral. The variable-temperature (2-300 K) magnetic susceptibilities at 0.7 T of both compounds have been measured. The interaction between the metal centers is moderately ferromagnetic; J = 16.6 cm(-1), g = 2.2, and D = -7.3 cm(-1) for 1 and J = 16.92 cm(-1), g = 2.2, and D(Ni1) = D(Ni2) = -6.41 cm(-1) for 2. Broken symmetry density functional calculations of exchange interaction have been performed on complexes 1 and 2 and provide a good numerical estimate of J values (15.8 cm(-1) for 1 and 15.35 cm(-1) for 2) compared to experiments. The role of Ni-N bond length asymmetry on the magnetic coupling has been noted by comparing the structures and J values of complexes 1 and 2 together with previously published dimers 3 (Eur. J. Inorg. Chem. 2009, 4982), 4 (Inorg. Chem. 2004, 43, 2427), and 5 (Dalton Trans. 2008, 6539). Our extensive DFT calculations reveal an important clue to the mechanism of coupling where the orientation of the magnetic orbitals seems to differ with asymmetry in the Ni-N bond lengths. This difference in orientation leads to a large change in the overlap integral between the magnetic orbitals and thus the magnetic coupling. DFT calculations have also been extended to develop several magneto-structural correlations in this type of complexes and the correlation aim to focus on the asymmetry of the Ni-N bond lengths reveal that the asymmetry plays a proactive role in governing the magnitude of the coupling. From a completely symmetric Ni-N bond length, two behaviors have been noted: with a decrease in bond length there is an increase in the ferromagnetic coupling, while an increase in the bond lengths leads to a decrease in ferromagnetic interaction. The later correlation is supported by experiments. The magnetic properties of 1, 2, and three previously reported related compounds have been discussed in light of the structural parameters and also in light of the theoretical correlations determined here.     

Study on the thermal behavior of the complexes of the type [PdX<Subscript>2</Subscript>(tdmPz)] (X = Cl<Superscript>−</Superscript>, Br<Superscript>−</Superscript>, I<Superscript>−</Superscript>, SCN<Superscript>−</Superscript>)

Four new mononuclear Pd(II) complexes of the type [PdX₂(tdmPz)] {X = Cl⁻ (1); Br⁻ (2); I⁻ (3); SCN⁻ (4); tdmPz = 1-thiocarbamoyl-3,5-dimethylpyrazole} have been synthesized and characterized by elemental analysis, IR spectroscopy, ¹H and ¹³C{¹H}-NMR experiments. The thermal behavior of the complexes 1–4 has been investigated by means of thermogravimetry (TG) and differential thermal analysis (DTA). From the initial decomposition temperatures, the thermal stability of the complexes can be ordered in the sequence: 3 < 4 ≡ 2 < 1. The final products of the thermal decompositions were characterized as metallic palladium by X-ray powder diffraction.     

Tuning high aqueous phase uptake in nonionic water-in-oil microemulsions for the synthesis of Mn-Zn ferrite nanoparticles: phase behavior, characterization, and nanoparticle synthesis

In this work, the formation of water-in-oil (w/o) microemulsions with high aqueous phase uptake in a nonionic surfactant system is investigated as potential media for the synthesis of Mn-Zn ferrite nanoparticles. A comprehensive study based on the phase behavior of systems containing precursor salts, on one hand, and precipitating agent, on the other hand, was carried out to identify key regions on (a) pseudoternary phase diagrams at constant temperature (50 °C), and (b) pseudobinary phase diagrams at constant surfactant (S):oil(O) weight ratio (S:O) as a function of temperature. The internal structure and dynamics of microemulsions were studied systematically by conductivity and self-diffusion coefficient determinations (FT PGSE (1)H NMR). It was found that nonpercolated w/o microemulsions could be obtained by appropriate tuning of composition variables and temperature, with aqueous phase concentrations as high as 36 wt % for precursor salts and 25 wt % for precipitating agent systems. Three compositions with three different dynamic behaviors (nonpercolated and percolated w/o, as well as bicontinuous microemulsions) were selected for the synthesis of Mn-Zn ferrites, resulting in nanoparticles with different characteristics. Spinel structure and superparamagnetic behavior were obtained. This study sets firm basis for a systematic study of Mn-Zn ferrite nanoparticle synthesis via different scenarios of microemulsion dynamics, which will contribute to a better understanding on the relationship of the characteristics of the obtained materials with the properties of the reaction media.     

Solvent- and temperature-dependent functionalisation of enantioenriched aziridines

A highly stereo‐ and regioselective functionalisation of chiral non‐racemic aziridines is reported. By starting from a parent enantioenriched aziridine and finely tuning the reaction conditions, it is possible to address the regio‐ and stereoselectivity of the lithiation/electrophile trapping sequence, thereby allowing the preparation of highly enantioenriched functionalised aziridines. From chiral N‐alkyl trans‐2,3‐diphenylaziridines (S,S)‐ 1 a , b , two differently configured chiral aziridinyllithiums could be generated (trans‐ 1 a , b‐Li in toluene and cis‐ 1 a , b‐Li in THF), thus disclosing a solvent‐dependent reactivity that is useful for the synthesis of chiral tri‐substituted aziridines with different stereochemistry. In contrast, chiral aziridine (S,S)‐ 1 c showed a temperature‐dependent reactivity to give chiral ortho‐lithiated aziridine 1 c‐ ortho ‐Li at ?78 °C and α‐lithiated aziridine 1 c‐α‐Li at 0 °C. Both lithiated intermediates react with electrophiles to give enantioenriched ortho‐ and α‐functionalised aziridines. The reaction of all the lithiated aziridines with carbonyl compounds furnished useful chiral hydroxyalkylated derivatives, the stereochemistry of which was ascertained by X‐ray and NMR spectroscopic analysis. The usefulness of chiral non‐racemic functionalised aziridines has been demonstrated by reductive ring‐opening reactions furnishing chiral amines that bear quaternary stereogenic centres and chiral 1,2‐, 1,3‐ and 1,5‐aminoalcohols. It is remarkable that the solvent‐dependent reactivity observed with (S,S)‐ 1 a , b permits the preparation of both the enantiomers of amines ( 11 and ent‐ 11 ) and 1,2‐aminoalcohols ( 13 and ent‐ 13 ) starting from the same parent aziridine. Interestingly, for the first time, a configurationally stable chiral α‐lithiated aziridine ( 1 c‐α‐Li ) has been generated at 0 °C. In addition, ortho‐hydroxyalkylated aziridines have been easily converted into chiral aminoalkyl phthalans, which are useful building blocks in medicinal chemistry.     

RNAs' uracil quartet model with a non-essential metal ion

We have recently communicated the resemblance of 1-hexyluracil in the crystal state with a lipid bilayer (CrystEngComm, 2010, 12, 362-365). Treatment of this molecule with silver nitrate yields a model, using a non-essential metal ion, of a uracil quartet with geometric parameters comparable to those previously found in RNA strands.     

Theoretical Study on Cooperativity Effects between Anion–π and Halogen‐Bonding Interactions

This article analyzes the interplay between lone pair–π (lp–π) or anion–π interactions and halogen‐bonding interactions. Interesting cooperativity effects are observed when lp/anion–π and halogen‐bonding interactions coexist in the same complex, and they are found even in systems in which the distance between the anion and halogen‐bond donor molecule is longer than 9 Å. These effects are studied theoretically in terms of energetic and geometric features of the complexes, which are computed by ab initio methods. Bader′s theory of “atoms in molecules” is used to characterize the interactions and to analyze their strengthening or weakening depending upon the variation of charge density at critical points. The physical nature of the interactions and cooperativity effects are studied by means of molecular interaction potential with polarization partition scheme. By taking advantage of all aforementioned computational methods, the present study examines how these interactions mutually influence each other. Additionally, experimental evidence for such interactions is obtained from the Cambridge Structural Database (CSD).