Studies of the synthesis and thermochemistry of coordinatively unsaturated chelate complexes (eta 5-C5Me5)IrL2 (L2 = TsNCH2CH2NTs, TsNCH2CO2, CO2CO2)

A comparative synthetic, structural, and thermochemical study on a series of chelate complexes containing the fragment (eta 5-C5Me5)Ir [(eta 5-C5Me5)Ir(TsNCH2CH2NTs) (1), (eta 5-C5Me5)Ir(TsNCH2CO2) (2), (eta 5-C5Me5)Ir(CO2CO2) (3)] was performed to clarify the roles of carboxylato and sulfonamido ligands. Whereas 1 and 2 are monomeric in solution and in the solid state, 3 appears to exist as an oligomer or polymer, (3)n, which can be broken up by addition of a ligand L such as a phosphine, CO, or 2-methoxypyridine to form (eta 5-C5Me5)Ir(L)(CO2CO2) (6). The synthesis of (3)n from [(eta 5-C5Me5)IrCl(mu-Cl)]2 required the use of silver oxalate in CH3CN, but if other solvents were used, the bridging oxalato complex (eta 5-C5Me5)IrCl(mu-eta 2-eta 2-C2O4)ClIr(eta 5-C5Me5) (7) was obtained and identified by X-ray diffraction. Enthalpies for reaction of THF-soluble monomers 1 and 2 with PMe3 were determined to be -28.7(0.5) and -28.5(0.4) kcal mol-1, respectively. The oligomerization behavior of 3 may be a result of reduced sigma- or pi-donation of carboxylato ligands compared to N-tosylamido ligands, because the values for nu CO in oxalato and bissulfonamido complexes 6-CO and (eta 5-C5Me5)Ir(CO)(TsNCH2CH2NTs) (4-CO) were 2064 and 2042 cm-1, respectively.     

Solvation of iron and chromium complexes in alcohol–water mixtures

Solubilities are reported for the perchlorates of five iron(II)-diimine complexes in t-BuOH–H₂O and one in MeOH–H₂O mixtures, for three iron(III)-3-hydroxy-4-pyranonate and three iron(III)-3-hydroxy-4-pyridinonate complexes in MeOH–H₂O and t-BuOH–H₂O, and for two chromium(III)-3-hydroxy-4-pyranonate complexes in MeOH–H₂O. Transfer chemical potentials are thence derived for the various iron(II), iron(III) and chromium(III) complexes, for transfer from H₂O into the respective mixed solvents (at 298.2 K). These results are combined with values reported earlier for related complexes, and for other alcohol–H₂O mixtures, to give an overall picture of solvation, expressed in the thermodynamic format of transfer chemical potentials, for iron(II)-diimine, iron(III)-3-hydroxy-4-pyridinonate and chromium(III)-3-hydroxy-4-pyranonate complexes in H₂O-rich aqueous-alcohol mixtures. Some spectroscopic (¹H-n.m.r.; i.r.) and kinetic (aquation rate constants at 298.2 K) data are reported for the chromium(III) complexes.     

Possible extensions of XIA's digital spectrometer technology to portable and remote monitoring instrumentation

The XIA DXP-4C, a 4 channel, CAMAC based X-ray spectrometer, is based on digitally processing directly digitized preamplifier signals. Designed for instrumenting multi-detector arrays for synchrotron radiation applications, the DXP-4C was optimized for very high count rates at a low cost per detector channel. These design constraints coincidentally lead to an instrument which is very compact and relatively low power (3.4 W/channel), considering its count rate and MCA capabilities, and which therefore offers interesting possibilities for effective extension to portable applications. Further, because all functions (gain, filter parameters, pileup inspection criteria and internal calibrations) are digitally controlled, the design can be readily adapted to a large variety of user interfaces, including remote access interfaces. Here we present the basics of the design and examine approaches to lowering the power to less than 300 mW/channel while retaining count rate capabilities in excess of 50,000 cps. We then consider the engineering issues associated with portable and remote spectrometry applications, examining in detail the three cases of a lead paint detector, a remote contamination monitor, and a space mission spectrometer.     

Comparison of the spectra of the cochlear microphonic and of the sound-elicited electrical impedance changes measured in scala media of the guinea pig

The harmonic structure of the cochlear microphonic (CM) and that of a sound-elicited signal which we have considered as an (apparent) changing resistance (CR) were simultaneously determined in scala media of the first turn of the guinea pig cochlea. We analyzed our data in the context of the Davis variable resistance hair-cell model (1965), which predicts CM and CR to be proportional to each other. But, plotted as functions of the sound-pressure level, CM and CR were found to have qualitatively similar but quantitatively disproportionate spectra. The preparations with the highest endolymphatic potential showed the least correspondence between the spectra of the two measured quantities. The phase angles of the fundamental components in CM and CR were equal within approximately 10 degrees, but the phase of the even harmonics of the two independent measures commonly differed by approximately 180 degrees at lower SPLs. Although most data were collected using 160-Hz tonal stimulation, tones with frequencies up to 1280 Hz produced qualitatively similar results. The CM and the CR both varied slightly with the level of the alternating current used to probe the CR. Considered on a quantitative basis, consistent with the accuracy of our measurements, any model which reduces to a fixed source, a fixed resistance, and a single linear, time-varying resistance cannot mimic the most significant, commonly found aspects of our CM and CR data. An alternate model incorporating a nonlinear, time-invariant resistance is able to account for some of the data. The output of the model is correctly considered a (time) changing resistance, or apparent changing resistance; but the model demonstrates that similar experimental results are not necessarily evidence for a time-varying resistor as originally proposed by Davis.     

An existence theorem for multimeron solutions to classical Yang-Mills field equations

In this paper we prove the existence of solutions to a class of boundary value problems for a singular nonlinear elliptic partial differential equation in a half plane. By a recent paper of J. Glimm and A. Jaffe, this proves the existence of multimeron solutions to the classical SU(2) Yang-Mills field equations in Euclidean space.Supported in part by the National Science Foundation under Grant PHY 77-18762Supported in part by the Icelandic Science FoundationSupported in part by Grant MCS 76-06524     

The crystal structure of the cation-disordered phase (Tl0.75Pb0.25)4Cl5

The 3 : 1 compound in the TlClPbCl₂ system crystallizes in the noncentrosymmetric space group P4₁2₁2 (D₄⁴) or its enantiomorph P4₃2₁2 D₄⁶). Lattice constants are a = 8.450(1)Å and c = 14.927(1)Å. Single-crystal X-ray diffraction data were collected using AgKα radiation. The structure was determined by analysis of Patterson and difference Fourier syntheses. Least-squares refinement of 41 parameters with 402 unique data converged with R_w = 0.036. In the structure the 12 Tl(I) and 4 Pb(II) ions are disordered over two eightfold sites. The formula is therefore appropriately written as (Tl_0.75Pb_0.25)₄Cl₅. A difference in size of the two positions suggests a preferential concentration of Pb(II) in the smaller site. The disordering of aliovalent cations together with a three-dimensional network of face-sharing polyhedra of cations surrounding the anions of the structure suggests (Tl_0.75Pb_0.25)₄Cl₅ as a particularly favorable case for enhancement of chloride ion conductivity by doping with TlCl. Irregularities in the coordination polyhedra about the cations can be explained by the presence of stereochemically active lone-pair electrons of the cations. The structure of (Tl_0.75Pb_0.25)₄Cl₅ is similar to that of the alloy Zr₅Si₄.