Freezing temperatures and enthalpies of dilution of aqueous solutions of amides. Gibbs energies and enthalpies of interaction of the N,N-dimethylamide group in aqueous solutions

Enthalpies of dilution, freezing temperatures, and densities of aqueous solutions of N,N-dimethylacetamide and N,N-dimethylpropionamide have been measured. Freezing temperatures of dilute aqueous solutions of formamide and N,N-dimethylformamide have also been measured. These data yield the pairwise molecular Gibbs energies and enthalpies of interaction: these have been treated according to a group additivity principle to give pairwise functional group Gibbs energies and enthalpies of interaction. The results indicate that substitution on the amide nitrogen may increase the Gibbs energy and enthalpy of interaction of the amide group with itself in an aqueous environment but the effect if present is small.     

Enthalpies of dilution of aqueous systems containing hexamethylenetetramine and other nonelectrolytes

Enthalpies of dilution of aqueous systems containing hexamethylenetetramine, alone and in ternary system with each of mannitol, myoinositol, cyclohexanol, formamide, dimethylformamide, and trioxane have been determined. The data have been treated in terms of the Savage-Wood additivity principle and first estimates for the pairwise groups interaction enthalpies of N/N, CH₂/N, CHOH/N, COHN/N and –O–/N have been made. The results are discussed in light of all other known group interaction enthalpies. The limitations and utilities of the Savage-Wood principle are reviewed.     

Transport of metal salts by zwitterionic ligands; simple but highly efficient salicylaldoxime extractants

Attaching dialkylaminomethyl arms to commercial phenolic oxime copper extractants yields reagents which transport base metal salts very efficiently by forming neutral 1 ratio 1 or 1 ratio 2 complexes with zwitterionic forms of the ligands.     

Design and Function of Pre‐organised Outer‐Sphere Amidopyridyl Extractants for Zinc(II) and Cobalt(II) Chlorometallates: The Role of C?H Hydrogen Bonds

Four new sterically hindered pyridines, L¹–L⁴‐containing amido substituents at the 2‐position act as efficient solvent extractants for [CoCl₄]^2? or [ZnCl₄]^2? from acidic chloride solutions through protonation of the pyridino N‐centre to form the neutral outer‐sphere complexes [(LH)₂MCl₄]. These ionophores show very high selectivity for chlorometallate anions over chloride ion and are readily stripped to liberate the free‐metal chlorides without the formation of inner‐sphere complexes [ML₂Cl₂]. Single‐crystal X‐ray structure determinations of [(L²H)₂CoCl₄] and [(L²H)₂ZnCl₄] (L²=2‐(4,6‐di‐tert‐butylpyridin‐2‐yl)‐N,N′‐dihexylmalonamide) coupled with ¹H NMR spectroscopy and DFT calculations on L²H⁺ and other complexes of [ZnCl₄]^2? confirm that the pyridinium NH group does not address the outer co‐ordination sphere of the metallanion, but rather forms a hydrogen bond to the pendant amide groups and thus pre‐organizes the ligand to present both C? H and amido N? H hydrogen‐bond donors to the [MCl₄]^2? ions. The selectivity for chlorometallates over chloride ions shown by this class of extractants arises from their ability to present several polarized C? H units towards the charge‐diffuse ions [MCl₄]^2?, whereas the smaller, “harder” chloride anion prefers to be associated with the amido N? H hydrogen‐bond donors.     

Piezochromism in nickel salicylaldoximato complexes: tuning crystal-field splitting with high pressure

The crystal structures of bis(3-fluoro-salicylaldoximato)nickel(II) and bis(3-methoxy-salicylaldoximato)nickel(II) have been determined at room temperature between ambient pressure and approximately 6?GPa. The principal effect of pressure is to reduce intermolecular contact distances. In the fluoro system molecules are stacked, and the Ni???Ni distance decreases from 3.19?? at ambient pressure to 2.82?? at 5.4?GPa. These data are similar to those observed in bis(dimethylglyoximato)nickel(II) over a similar pressure range, though contrary to that system, and in spite of their structural similarity, the salicyloximato does not become conducting at high pressure. Ni-ligand distances also shorten, on average by 0.017 and 0.011?? for the fluoro and methoxy complexes, respectively. Bond compression is small if the bond in question is directed towards an interstitial void. A band at 620?nm, which occurs in the visible spectrum of each derivative, can be assigned to a transition to an antibonding molecular orbital based on the metal 3d(x(2)-y(2)) orbital. Time-dependent density functional theory calculations show that the energy of this orbital is sensitive to pressure, increasing in energy as the Ni-ligand distances are compressed, and consequently increasing the energy of the transition. The resulting blueshift of the UV-visible band leads to piezochromism, and crystals of both complexes, which are green at ambient pressure, become red at 5?GPa.     

Design of base metal extractants. Part 1. Inter-ligand hydrogen bonding in the assembly of pseudo-macrocyclic bis(aminosulfonamidato)M(II) complexes

Monosulfonyl derivatives of simple 1,2- and 1,3-diamines (R2HN-R-NHSO2R1 = L) have been shown to be easily deprotonated to give neutral 2:1 complexes, [M(L - H)(2)], with Co(II), Ni(II), Cu(II) or Zn(II). The Ni(II) and Cu(II) complexes with deprotonated N-tosyl-1,2-diaminoethane have a planar N4(2-) donor set and a 14-membered pseudo-macrocyclic structure based on head-to-tail S=O...H-N((amine)) bonding between the two bidentate ligands. In the related tetrahedral Zn(II) complex the ends of the mutually perpendicular bidentate N2- units are too far apart to form a cyclic H-bonded system. X-Ray structure determinations on five free ligands provide evidence for extensive inter-molecular H-bonding, which in the case of N-tosyl-1,3-diaminopropane and its N'-tert-butyl derivative involves formation of dimeric 16-membered pseudo-macrocycles. Despite favourable inter-ligand H-bonding in the neutral 2:1 complexes, these ligands are relatively weak extractants, showing >50% loading of Cu(II) in "pH-swing" equilibria, 2L(org)+ M2+ = [M(L - H)2](org)+ 2 H+, only when the pH of the aqueous phase is raised above 4.     

The one-pot halomethylation of 5-substituted salicylaldehydes as convenient precursors for the preparation of heteroditopic ligands for the binding of metal salts

The one-pot bromo- and chloro-methylation of various 5-substituted salicylaldehydes with paraformaldehyde and hydrobromic or hydrochloric acid has been achieved. This approach establishes a convenient and flexible method to attach functional arms to salicylaldehydes for further applications in organic and coordination chemistry. Examples are described using 3-bromomethyl-5-t-butylsalicylaldehyde in the synthesis of piperazine-containing heteroditopic ligands as receptors for metal salts.     

High voltage pulses for high impedance loads using explosive formedfuses

Explosive formed fuses (EFFs) use conducting elements that are deformed by explosive pressure (typically, against dielectric dies). This causes the fuse geometry to change, so that the conducting element cross section decreases. This enables a higher ratio of current conduction to current interrupt time than for normal fuses, and it enables more control of when current interruption occurs. In combination with a suitable output closing switch, EFF's can be used to obtain several hundred kilovolt voltage pulses from inductive stores to drive several ohm loads. With proper choices of inductive store, EFF geometry and material, and output closing switch features, such a voltage pulse can be approximately flat topped for microsecond duration and have a small fraction of microsecond risetime. We present theoretical analysis and circuit simulations which illustrate this, using scaled empirical EFF parameters for inductive stores in the 1 weber flux, several hundred nanohenry range. The circuit simulations were done using MicroCap-IV, with user defined elements. These simulations were done with static inductive stores and with explosive magnetic flux compression generators driving inductive stores     

Synthesis of a new class of β-iodo N-alkenyl 2-pyridones

A new method for the synthesis of β-iodo N-alkenyl 2-pyridones from substituted 2-propargyloxypyridines has been discovered . These compounds present a unique complement of orthogonal functionality and structural characteristics that are unavailable via other routes. The ready access to these compounds renders them an important entry point for the preparation of more complex N-alkyl pyridone-containing targets.