Life span of a local structure in colloidal suspensions

Abstract

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.

Inhomogeneity of solute distribution in ionic systems

“…In this section, we discuss how the structural inhomogeneity varies with time only briefly, since detailed accounts have already been given by us. 22,24,25 First the ordering of latices was confirmed by the microscope and then the structure was destroyed by addition of sodium chloride (at a concentration of mol dmP3). The crystallisation was allowed to take place by putting ion-exchange resin beads in the suspension, which removed the added salt ions.…”