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) in apolar hydrocarbons have been investigated. The small angle scattering (SAS) technique (neutron and X-rays) is used to characterize the structures of the supramolecular assemblies. Copper(II) and rhodium(II) derivatives form 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 long and semirigid, and its cross section is heterogeneous with an organometallic 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 entangled and coexist with a fraction of much smaller rods. A "composite network model" is proposed to account for the various scattering situations. Birefringence measurements support the existence of bundles of rods in the system. The network is described more as a dispersion of heterogeneities (or junction zones) that are randomly dispersed and connected through the mixture of rods and wires than as coils in good solvent conditions in the manner of polymeric semidilute solutions. Structural effects of an endcapping molecule have been examined through the scattering and birefringence signatures.