Synthesis and Characterization of Strongly Solvatochromic Molybdenum(III) Complexes

A series of seven molybdenum(III) complexes with the general formula of [Mo(diimine)Cl₄]^- were synthesized and characterized by X-ray diffraction, IR, cyclic voltammetry (CV), and UV-vis. The complexes were discovered to be highly solvatochromic, showing shifts in λ_max between ∼120 and 170 nm in solvents ranging from water to acetone. Varying the substituents on the diimine ligand influenced the absorption energy such that electron-withdrawing groups induced a red shift while electron-donating groups exhibited the opposite effect. The complexes were surprisingly stable in both acidic and basic solutions, and in the case where carboxylic acid substituents were present, additional shifts in the absorption maxima were observed, corresponding to the state of protonation of these groups. Both the Mo^IV/III and Mo^III/II redox couples were observed in CV experiments and were complemented with density functional theory (DFT) calculations.

Interfacial properties modulated by the water confinement in reverse micelles created by the ionic liquid-like surfactant bmim-AOT

The behavior of the interfacial water entrapped in reverse micelles (RMs) that were formed by the ionic liquid-like surfactant 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (bmim-AOT) was investigated with the use of UV-Vis absorption spectroscopy and nuclear magnetic resonance (NMR) relaxometry. The solvatochromism of two molecular probes, namely, 1-methyl-8-oxyquinolinium betaine (QB) and N,N,N',N'-tetramethylethylenediamine copper(ii)acetylacetonate tetraphenylborate ([Cu(acac)(tmen)][B(C6H5)4]), was investigated. As a comparison, the analog RMs formed by sodium 1,4-bis-2-ethylhexylsulfosuccinate (Na-AOT) were also explored. By varying the water content inside the RMs and consequently the different magnitude of the water-surfactant interactions at the interface, interesting properties were observed by comparing bmim-AOT and Na-AOT RMs. From the solvatochromic behavior of ([Cu(acac)(tmen)][B(C6H5)4]), we found that the interface in bmim-AOT RMs shows a smaller electron donating capacity than that in Na-AOT RMs. QB revealed that the interfacial region is a weaker hydrogen bond donor and less polar than the corresponding Na-AOT RMs. NMR experiments showed that the molecular motion of water in bmim-AOT RMs is less restricted than that of the water molecules confined in Na-AOT RMs. In summary, the results show how the nature of the bmim+ cation affects the interaction between the entrapped water and the RM interface, greatly modifying the interfacial water structure in comparison with the results known for Na-AOT.

The impact of ionic liquids on the coordination of anions with solvatochromic copper complexes

Traditionally weakly associating anions demonstrate a stronger than expected level of coordinating ability within ILs.

Colloidal interaction in ionic liquids: effects of ionic structures and surface chemistry on rheology of silica colloidal dispersions

To understand the important factors that dominate colloidal stability in ionic liquids (ILs), rheology of the dispersions of hydrophilic and hydrophobic silica nanoparticles were investigated in ILs with different ionic structures. The dispersion of hydrophilic silica nanoparticles in [BF(4)] anion-based ILs and in an IL containing a hydroxyl group, 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethane sulfonyl)amide ([C(2)OHmim][NTf(2)]), showed an intriguing shear thickening response. Nonflocculation of the hydrophilic silica nanoparticles in the [BF(4)] anion-based ILs and in [C(2)OHmim][NTf(2)], where the interparticle electrostatic repulsion appears to be depressed, suggests that an IL-based steric hindrance or solvation force provides an effective repulsive barrier for the colloidal aggregation. On the other hand, the other dispersions presented shear thinning behavior with an increase in shear rates and gelled at relatively low particle concentrations. The elastic modulus (G') of the gels formed by the hydrophilic silica was correlated with the polarity scale, lambda(Cu), of the ILs, indicating that the silica-IL interactions, especially the silica-anion interactions, appear to affect the rheological behavior, even in flocculated systems. All the ILs used in this study can be solidified by the addition of hydrophobic silica particles. The rheological behavior of the silica colloidal dispersions was strongly affected by the ionic structure of the ILs and the surface structure of the silica particles.

How ionic are room-temperature ionic liquids? An indicator of the physicochemical properties

Room-temperature ionic liquids (RTILs) are liquids consisting entirely of ions, and their important properties, e.g., negligible vapor pressure, are considered to result from the ionic nature. However, we do not know how ionic the RTILs are. The ionic nature of the RTILs is defined in this study as the molar conductivity ratio (Lambda(imp)/Lambda(NMR)), calculated from the molar conductivity measured by the electrochemical impedance method (Lambda(imp)) and that estimated by use of pulse-field-gradient spin-echo NMR ionic self-diffusion coefficients and the Nernst-Einstein relation (Lambda(NMR)). This ratio is compared with solvatochromic polarity scales: anionic donor ability (Lewis basicity), E(T)(30), hydrogen bond donor acidity (alpha), and dipolarity/polarizability (pi), as well as NMR chemical shifts. The Lambda(imp)/Lambda(NMR) well illustrates the degree of cation-anion aggregation in the RTILs at equilibrium, which can be explained by the effects of anionic donor and cationic acceptor abilities for the RTILs having different anionic and cationic backbone structures with fixed counterparts, and by the inductive and dispersive forces for the various alkyl chain lengths in the cations. As a measure of the electrostatic interaction of the RTILs, the effective ionic concentration (C(eff)), which is a dominant parameter for the electrostatic forces of the RTILs, was introduced as the product of Lambda(imp)/Lambda(NMR) and the molar concentration and was compared with some physical properties, such as reported normal boiling points and distillation rates, glass transition temperature, and viscosity. A decrease in C(eff) of the RTILs is well correlated with the normal boiling point and distillation rate, whereas the liquid-state dynamics is controlled by a subtle balance between the electrostatic and other intermolecular forces.

Evidence of solvent coordination in mixed-ligand copper(II) chelates. Crystal and molecular structure of aquo(N,N,N′,N′-tetramethyl-1,2-diaminoethane) (3-cyano-2,4-pentanedionato)copper(II) perchlorate

The structure of the title compound [Cu(CN-acac)H2O(Me4en)]ClO4(C12H24ClCuN3O7) was determined by X-ray diffraction studies. The structure is orthorhombic, space group Pbca, Z = 8, a = 10.302 Å, b = 15.971 Å, c = 22.945 Å and ϱ x = 1.483 Mgm−3. The water molecule is covalently bonded to copper. The structure around the central copper atom is distorted square pyramidal with the apex occupied by the oxygen atom of the water molecule and the base formed by the oxygen atoms of the β-dionato (3-cyano-2,4-pentanedionato) moiety and the nitrogen atoms of the N,N,N′,N′-tetramethyl-1,2-diaminoethane, Me4en. As a result of this coordination a resonance-stabilised, planar, six-membered β-dionato chelate ring and a five-membered chelate ring with the 1,2-diamine ligand in the gauche conformation are formed. The Perchlorate ion, ClO4 − interacts electrostatically with the [Cu(CN-acac)H2O(Me4en)] entity and forms hydrogen bonds with a hydrogen atom of the water molecule.