The dynamic aspects in latex particle dispersions were studied using video imagery combined with an image data analyzer and Kossel line analysis. The lattice vibrations and lattice defects in the colloidal crystals were demonstrated. The trajectories of particles in the ordered regions were shown to be quite different from those in coexisting disordered regions. The kinetics of (2D) crystal growth was followed by using the microscopic information (as a density function) and its Fourier transformation. The process was also followed by the radial distribution function g(r), which was obtained by direct measurements of interparticle distances. The Ostwald ripening mechanism was confirmed in the process of crystallization.

Two-dimensional (2D) Fourier transformation was carried out for particle distribution in highly purified polymer latex suspensions by use of a digital-image-processing system. The particle; distributions were photographed by an optical microscope for larger particles ( & approximately 0.2 pm in diameter) at various temperatures and particle charges. The interparticle distance (2D, "", ) calculated from the halo pattern in the Fourier image hardly changed with increasing temperature (i.e. , with decreasing dielectric constant for water), and decreased with particle charges. Preliminary quasielastic light scattering (QELS) was carried out independently for smaller particles ( & approximately 0.2 pm in diameter) and furnished broad peaks in the interference function. The 2D, "~, obtained from the peak of the interference function was smaller than 2Do (average interparticle distance calculated from concentration). The 2D, "~, was found to decrease with increasing particle charges and with decreasing dielectric constant. The trend observed by QELS was consistent with the results of 2D Fourier transformation, and with our previous claim that there exists electrostatic attraction among the particles through the intermediary of counterions (in addition to short-range repulsion). In the QELS experiments, the etfect of the particle sedimentation on 2D, "~, was investigated by changing the specific gravity of the dispersion medium using mixtures of 820 and D&O.No significant change was detected in the peak position with solvent composition. The 2D Fourier transformation and QELS measurements were carried out finally for the same latex particles (diameter -0.1-0.2 p, m). The value of 2D, "~, estimated by the two methods was roughly the same and the numbers of halo rings and broad scattering peaks coincided. It is now clear that the broad peaks in the interference function obtained from the QELS measurements corresponded to the two-state structure directly observed by the microscopic method. This provides strong support to our previous interpretation that the single broad peak(s) observed by other scattering methods reflect(s) the translational ordering of ionic species.

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orbital to match ± and thus constrains the acetylene to twoelectron donation. The pyramidal IrP3+ fragment (leading to Td or Cx) has the requisite three orbitals in the form of the 2e and 2a of a regular C3" IrP3+ pyramid:1 23456789 *es (one of the 2e set) matches 7rj_, 2a matches 8, and ea (from the 2e pair) is close in energy to 7rj|*. The acetylene is thus a formal four-electron donor. Optimizing this last interaction significantly increases the metal/acetylene bonding, and this is accomplished by pointing the two lobes of the ea more toward the acetylene carbons. In terms of nuclear motions, this is achieved by bending the two Ir-P bonds toward the IrC2 plane, which converts the Td to the Cs structure. >o es ea 2a Reaction of Ir(MeC2Me)P3+ with H2 (1 atm) at 25 °C in CD2C12 yields butane (no butenes) and IrH4P3+, which closes the cycle of Scheme I. Further mechanistic details of the steps in this scheme, together with a broader survey of the reactivity of Ir(MeC2Me)P3+, are currently under investigation.Acknowledgment. We thank the NSF (Grant No. 8707055) for financial support and Johnson-Matthey Co. for material support. O.E. acknowledges the Indiana University Institute for Advanced Study for a fellowship which enabled this collaboration. Scott Horn is thanked for skilled technical assistance. The Laboratoire de Chimie Théorique is associated with the CNRS (UA506) and is a member of ICMO and IPCM. Supplementary Material Available: Tables of positional and thermal parameters for [Ir(MeC2Me)(PMe2Ph)3]BF4 and a figure showing thermal ellipsoids (5 pages). Ordering information is given on any current masthead page.

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