Potentiometric Study of Lanthanide Salicylaldimine Schiff Base Complexes

Formation of complexes between the lanthanide ions and N,N′-bis(salicylidene)-4-methyl-1,3-phenylenediamine ligand was studied in solution by pH potentiometry. The potentiometric titration was performed at 25.00 °C in 0.1 mol·dm^?3 NaClO₄ ionic strength and in DMSO:water (30:70 v:v) solvent mixture. N,N′-bis(salicylidene)-4-methyl-1,3-phenylenediamine ligand (H₂L) occurs in three forms: fully or partially deprotonated and unionized. Computer analysis of potentiometric data indicated that in solution the lanthanide (Ln) complexes exist as LnL₂, Ln(HL)₂ and Ln(H₂L)₂ species. This observation appears to be in contrast to the solid-state behavior of these complexes prepared in a self-assembly process and structurally defined. Stability constants for La³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Ho³⁺ and Lu³⁺ (Ln³⁺) complexes were determined. The order of stabilities of LnL₂ species in terms of metal ions is La³⁺ > Eu³⁺ ≈ Gd³⁺ = Tb³⁺ < Ho³⁺ < Lu³⁺ with a prominent “gadolinium break”.     

Path components of the space of gradient vector fields on the two-dimensional disc

We present a short proof that if two gradient maps on the two-dimensional disc have the same degree, then they are gradient homotopic.     

Enantioselective Synthesis of Chiral Carboxylic Acids from Alkynes and Formic Acid by Nickel-Catalyzed Cascade Reactions: Facile Synthesis of Profens

We report a stereoselective conversion of terminal alkynes to α-chiral carboxylic acids using a nickel-catalyzed domino hydrocarboxylation-transfer hydrogenation reaction. A simple nickel/BenzP* catalyst displayed high activity in both steps of regioselective hydrocarboxylation of alkynes and subsequent asymmetric transfer hydrogenation. The reaction was successfully applied in enantioselective preparation of three nonsteroidal anti-inflammatory profens (>90 % ees) and the chiral fragment of AZD2716.     

Thermal Conductivity of Ionic Liquids: Recent Challenges Facing Theory and Experiment

Journal of Solution Chemistry - Recently ionic liquids have been considered as prospective substances for application as heat transfer fluids, which requires accurate knowledge of their thermal...     

2D time-domain nuclear magnetic resonance (2D TD-NMR) characterization of cell wall water of Fagus sylvatica and Pinus taeda L.

Cellulose - Water dominates the wood cell wall in the hygroscopic range. The state and amount of cell wall water influence the physical and mechanical properties of wood. 2D time-domain nuclear...     

Spatiotemporal Studies of the One-Dimensional Coordination Polymer [Fe(ebtz)2(C2H5CN)2](BF4)2: Tug of War between the Nitrile Reorientation Versus Crystal Lattice as a Tool for Tuning the Spin Crossover Properties**

Reaction of 1,2-di(tetrazol-2-yl)ethane (ebtz) with Fe(BF₄)₂⋅6 H₂O in different nitriles yields one-dimensional coordination polymers [Fe(ebtz)₂(RCN)₂](BF₄)₂⋅nRCN (n=2 for R=CH₃ ( 1 ) and n=0 for R=C₂H₅ ( 2 ) C₃H₇ ( 3 ), C₃H₅ ( 4 ), CH₂Cl ( 5 )) exhibiting spin crossover (SCO). SCO in 1 and 3 – 5 is complete and occurs above 160 K. In 2 , it is shifted to lower temperatures and is accompanied by wide hysteresis (T_1/2^↓=78 K, T_1/2^↑=123 K) and proceeds extremely slowly. Isothermal (80 K) time-resolved single-crystal X-ray diffraction studies revealed a complex nature for the HS→LS transition in 2 . An initial, slow stage is associated with shrinkage of polymeric chains and with reduction of volume at 77 % (in relation to the difference between cell volumes V_HS−V_LS) whereas only 16 % of iron(II) ions change spin state. In the second stage, an abrupt SCO occurs, associated with breathing of the crystal lattice along the direction of the Fe–nitrile bonds, while the nitriles reorient. HS→LS switching triggered by light (808 nm) reveals the coupling of spin state and nitrile orientation. The importance of this coupling was confirmed by studies of [Fe(ebtz)₂(C₂H₅CN/C₃H₇CN)₂](BF₄)₂ mixed crystals ( 2 a , 2 b ), showing a shift of T_1/2 to higher values and narrowing of the hysteresis loop concomitant with an increase of the fraction of butyronitrile. This increase reduces the capability of nitrile molecules to reorient. Density functional theory (DFT) studies of models of 1 – 5 suggest a particular possibility of 2 to adopt a low (140–145°) value of its Fe-N-C(propionitrile) angle.