Polyhapto-aromatic interactions in lead(II) coordination

In its crystalline form, the Pb(II) complex of 1,3-diphenylpropane-1,3-dionate (dibenzoylmethanide, DBM(-)) can be regarded as containing polymeric chains of centrosymmetric, dimeric Pb(2)(DBM)(4) units linked through hexahapto interactions of the Pb atoms with phenyl groups from adjacent units. Each Pb atom also appears to be involved in intraunit dihapto-aromatic interactions, thus attaining a total hapticity of thirteen. Comparison with the analogous Sn(II) compound indicates that the unusually high coordination number may reflect the capacity of Pb(II) to act as both a Lewis acid and a Lewis base.     

Phosphorus-phosphorus coupling in a diphosphine with a ten bond P...P separation

The large, unsymmetrical diphosphine 5,11,17,23-tetra-tert-butyl-25,26-bis(diphenylphosphinomethoxy)-27(or 28)-benzoyloxy-28(or 27)-hydroxycalix[4]arene, in which the phosphorus atoms are separated by ten bonds, was prepared by monobenzoylation of 5,11,17,23-tetra-tert-butyl-25,26-bis(diphenylphosphinoylmethoxy)-27,28-bis(hydroxy)calix[4]arene, followed by reduction with phenyl silane. Its molecular structure has been determined by X-ray crystallography. In the solid state, the phosphorus atoms are separated by 5.333(1) A. NMR investigations reveal an unexpected "through-space"J(PP') coupling constant of 8.0 Hz and also show that, in solution, the calixarene is conformationally mobile, the phenoxy ring flipping rapidly through the calixarene annulus. The spatial proximity of the two phosphorus atoms was further demonstrated by the ease of obtaining the cis-chelate complex [Pd(eta3-C3H4Me)(THF)2]BF4 (THF = tetrahydrofuran).     

Messages in molecules: ligand/cation coding and self-recognition in a constitutionally dynamic system of heterometallic double helicates

Double helicates are known to exhibit self-recognition characteristics determined by the coordination geometry of the metal involved as well as by the topicity of the ligands. Combining tridentate (terpyridine, T) or bidentate (bipyridine, B) subunits in a tritopic strand affords a set of ligands able to assemble by pairs to form double helicates, homo- or heterostranded, homo- or heterotopic, depending on the coordination properties of the metals involved. The four ligand strands, BBB, TTT, BBT, and TBT form constitutionally dynamic sets of double helicates with the metal ions Cu(I), Cu(II), and Zn(II); these helicates correspond to the correct coding of the BB, BT, and TT pairs for tetra-, penta-, and hexacoordinate Cu(I), Cu(II), and Zn(II) cations, respectively.     

Differential non-destructive image current detection in a fourier transform quadrupole ion trap

Dual-detector differential non-destructive Fourier transform detection in a quadrupole ion trap is shown to improve signal intensity and reduce noise compared with spectra recorded using a single detector. A larger area detector in each end-cap electrode is machined to fit its hyperbolic shape and so minimize field imperfections on the z-axis. Argon, acetophenone and bromobenzene spectra were recorded to allow a comparison between single- and dual-detector (differential) modes of detection and to demonstrate the improvement achieved with differential detection. Copyright 1999 John Wiley & Sons, Ltd.     

Ditopic Calixcrowns with Inequivalent Crown Loops: Synthesis and Structural Characterisation of an Unsymmetrical Calix[4]arene biscrown-6

Consecutive base-catalysed reactions of calix[4]arene with the ditosylates of two different polyetherdiols result in the relatively efficient production of an unsymmetrical calix biscrown-6 which, after reduction of an ethoxycarbonyl substituent to an hydroxymethyl group, has been characterised structurally by a room-temperature, single crystal X-ray study of its chloroform solvate. Crystals of ( 4), C53H62O13... 0.57CHCl3, are triclinic, P¯1, a 18.95(3), b 12.394(9), c 11.756(7) Å 106.93(5), 101.77(8), 94.63(8)°, Z = 2; R was 0.088 for 2231 observed' (I > 3(I)) diffractometer data.     

Conical cavitands as second coordination spheres and protecting environments. Towards metal-centred, intra-cavity reactions

Metallocavitands are coordination compounds based on rigidified molecular cavities which possess at least one entry. Those in which the metal centre is rigidly held above the entrance are particularly promising for the study of host-guest interactions between metal-bonded substrates and the internal part of a cavity. Such systems also open the way to highly selective intra-cavity reactions. The present review focusses on conical cavities derived from calixarenes and cyclodextrins and examines their possible use as second coordination sphere ligands.     

Carboxymethylated cage amines: coordination and lactamization

Depending upon the position and degree of substitution, carboxymethyl derivatives of cage amines of the "sarcophagine" (3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane) type vary considerably in the stability of their lactamized forms. For 1,8-diamino-3-carboxymethylsarcophagine, L(1), only indirect evidence for some involvement of a lactamized form of its Ni(II) complex has been obtained. Crystal structure determinations for [Cu(H(2)L(1))](NO(3))(3.5)Cl(0.5) x 2.5H(2)O and [Ni(HL(1))]Cl(3) x 3H(2)O show distorted octahedral coordination of all six endocyclic N-donor atoms in both cases. For related diaminosarcophagine derivatives with either two (1,8; L(2)) or three (1,1,8; L(3)) carboxymethyl substituents on the exocyclic N atoms, crystallographic studies have shown a dilactam form for the ligands in their Ni(II) and Cu(II) complexes which is of almost identical conformation to that of the diprotonated "free" ligand in [H(2)L(3)][ZnCl(4)] x 6H(2)O. The lactamized ligands appear to strongly favor square planar four-coordination, and the Co(II) complex of L(2) shows a remarkable lack of reactivity toward oxygen. Kinetic studies indicate that the hydrolytic stability of the lactam rings is comparable to that of uncoordinated analogues.     

Pseudo-steady-state solutions for solidification in a wedge

Polubarinova-Kochina's analytical differential equation methodis used to determine the pseudo-steady-state solution to problemsinvolving the freezing (solidification) of wedges of liquidwhich are initially at their fusion temperature. In particular,we consider four distinct problems for wedges which are: freezingwith the same constant boundary temperature, freezing with thesame constant boundary heat fluxes, freezing with distinct constantboundary temperatures and freezing with distinct constant fluxesat the boundaries. For the last two problems, a Heun's differentialequation with an unknown singularity is derived, which in bothcases admits a particularly elegant simple solution for thespecial case when the wedge angle is . The moving boundariesobtained are shown pictorially.