Structure of a transient network made up of entangled monomolecular organometallic wires in organic liquids. Effects of an endcapping molecule

Viscoelastic solutions of a family of bimetallic tetracarboxylates (M2R4) i n apolar hydrocarbons have been investigated. The small angle scattering (S AS) technique (neutron and X-rays) is used to characterize the structures o f the supramolecular assemblies. Copper(II) and rhodium(II) derivatives for m very thin molecular rodlike species (r(Cu2R4) approximate to 8.5 Angstrom ) with only one molecule per diameter. With Cu-2(Et/C-8)(4), the wire is lo ng and semirigid, and its cross section is heterogeneous with an organometa llic core embedded in an aliphatic shell. The investigation of the topology of the network as a function of the carboxylate type (metal and aliphatic substitution) and concentration is detailed. The monomolecular wires are en tangled and coexist with a fraction of much smaller rods. A "composite netw ork model" is proposed to account for the various scattering situations. Bi refringence measurements support the existence of bundles of rods in the sy stem. The network is described more as a dispersion of heterogeneities (or junction zones) that are randomly dispersed and connected through the mixtu re of rods and wires than as coils in good solvent conditions in the manner of polymeric semidilute solutions. Structural effects of an endcapping mol ecule have been examined through the scattering and birefringence signature s.