Inorganic Chemistry in taking spectra. Some metal complex syntheses were performed by P. B. Bowman. Elemental analyses were done by C. S. Yeh. This research was supported in part by The United States Atomic Energy Commission under Contract AT(11-1)-1222.Contribution from the Departments of Chemistry,

No abstract

The focus of this article is an examination of chemical reaction mechanisms in ionic liquids. These mechanisms are compared with those pertaining to the same reactions carried out in conventional solvents. In cases where the mechanisms differ, attempts to provide an explanation in terms of the chemical and physicochemical properties of the reactants and of the components of the ionic liquids are described. A wide range of reactions from different branches of chemistry has been selected for this purpose. A sufficient background for student readers has been included. This tutorial review should also be of interest to kineticists, and to both new and experienced investigators in the ionic liquids field.

Spectroscopic, thermodynamic, and kinetic measurements have been made on aqueous solutions of copper(II) complexes of hexamethylated tren and trimethylated tren (one methylation per primary amine group of tren) with the objective of correlating the influence of geometry (trigonal bipyramidal, evident from UV/vis spectroscopy) and N-alkyl substitution in the ligand on these inherent properties. At 25.0 degrees C the protonation constants of Me(3)tren are not significantly different from those of tren and Me(6)tren, and the stability constant for the Cu(II) complex is of the same order of magnitude as that for the [Cu(tren)(H(2)O)](2+) complex ion. The pK(a) for deprotonation of the coordinated water molecule of [Cu(Me(3)tren)(H(2)O)](2+) is intermediate between the values for the complexes containing the unsubstituted and the fully substituted tren ligand. Substitution (pyridine for water) kinetics measurements employing stopped-flow and temperature-jump methods revealed different patterns of reactivity: pyridine replaces water in [Cu(Me(3)tren)(H(2)O)](2+) with a second-order rate constant of (4.4 +/- 0.8) x 10(2) M(-)(1) s(-)(1) at 25.0 degrees C, whereas the corresponding process for [Cu(Me(6)tren)(H(2)O)](2+) is relatively complex and is discussed in more detail. Substitution in the former complex ion is characterized in the forward and reverse directions, by DeltaH() = 60 +/- 8 and 51.9 +/- 0.9 kJ mol(-)(1), DeltaS() = 5 +/- 27 and -23 +/- 3 J mol(-)(1) K(-)(1), and DeltaV() = -8.7 +/- 4.6 and -6.2 +/- 1.1 cm(3) mol(-)(1), respectively. It is concluded that this reaction follows an I(a) mechanism, similar to that reported for the comparable reaction of [Cu(tren)(H(2)O)](2+). An X-ray structural determination on a crystal of [Cu(2)(Me(3)tren)(2)(CN)](ClO(4))(3).2CH(3)CN demonstrated trigonal bipyramidal geometry about each copper(II) center. As has been found in comparable complexes of tren and Me(6)tren, the axial nitrogen to copper bond is shorter than the equatorial nitrogen-copper bonds, and the angle made by N(axial)-Cu-N(equatorial) is less than 90 degrees (84.6-85.4 degrees ), signifying that each copper ion lies below the plane of the equatorial nitrogen atoms.

Mixtures of gelatin and maltodextrin in aqueous solution have been quenched to temperatures at which they are initially miscible but where gelatin ordering is initiated. In many cases phase separation was observed to occur after a significant time delay, and the dependence of these delays on quench temperature and biopolymer concentration has been studied in detail using turbidity measurements and confocal laser scanning microscopy (CLSM). Furthermore, by observing the optical rotation (OR) and turbidity of the system simultaneously, the gelatin helix content and the time delay before the onset of phase separation were monitored concurrently. The observed delay times were found to correspond to the time taken for the development of a certain degree of gelatin ordering, which drives the separation process. A further consequence of gelatin ordering is the viscosifying of the solution and, at sufficient concentrations, the formation of a gel. Therefore, rheological measurements have been used in addition to turbidity measurements and CLSM in order to monitor further the structural development of the systems. A comparison of the data obtained from these techniques shows that while the development of a certain elasticity will trap the system morphology, this elasticity is not directly related to that found at the gel point. At low maltodextrin concentrations, where phase separation was not detected by turbidity, transmission electron microscopy (TEM) has been used to examine the microstructure on a smaller length scale.

No abstract

No abstract

The tripodal tetramine ligands N(CH2CH2CH2NH2)3 (trpn) and N[(CH2CH2CH2NH2)2(CH2CH2NH2)] (332) react with Cu(NO3)2·3H2O in water to give light blue copper(II) complexes. These were characterized by X-ray crystallography to be the square-pyramidal binuclear Cu(II) species [Cu(trpn)(NO3)]2(NO3)2 and [Cu(332)(NO3)]2(NO3)2·2H2O. Selected crystallographic details are as follows, respectively:  formula C18H48Cu2N12O12, C16H48Cu2N12O14; M = 751.74, 759.72 Da; both triclinic; both P1̄; a = 8.4346(8), 8.446(4) Å; b = 9.0785(9), 8.744(3) Å; c = 11.9310(12), 12.007(3) Å; α = 94.50(1), 102.68(2)°; β = 103.56(1), 94.79(3)°; γ = 117.42(1), 117.69(4)°; V = 769.7(5), 748.2(13) Å3; both Z = 1; R = 4.16, 4.00; R w = 11.34, 6.74 for 2887 (I ≥ 2σ(I)), 2457 (F o 2 ≥ 3σ(F o 2)) structure factors and 199, 209 refined parameters. The binuclear complex dications exhibit a square-pyramidal coordination geometry around the copper atoms. Three amine functions (one tertiary and two primary) are coordinated to one copper atom and the remaining primary amine arm bridges to the second copper center. Potentiometric and visible spectrophotometric studies show that a protonated square-pyramidal [Cu(HL)(H2O)2]3+ cation (L = trpn, 332, 322 (322 = N[(CH2CH2CH2NH2)(CH2CH2NH2)2])) predominates in the intermediate pH region, in contrast to the established trigonal-bipyramidal structure of the tren (tren = tris(2-aminoethyl)amine)) complex of Cu(II). Each [Cu(HL)(H2O)2]3+ has one protonated uncoordinated ligand arm which explains the formation of the binuclear species at neutral pH.