Chemical stability and characterization of rhodium-diisocyanide coordination polymers

Poly-[Rh(1,4-phenylene diisocyanide)_4/2⁺(Cl) ^-] has a two-dimensional template structure, where Rh atoms are bonded by the π-conjugated 1,4-phenylene diisocyanide (pdi) ligands in the x - y plane and through overlapping d_z- orbitais in the z direction. The more conductive metallic bonds in the z direction create anisotropy in the electrical conductivity. The anisotropy and unique geometry of poly-[Rh(pdi)_4/2⁺(Cl)^-] make it a useful test bed for examining the relationship between electrical properties and chemical stability in metal-isocyanide molecular wire systems. The bulk powder of poly-[Rh(pdi)_4/2⁺(Cl)"] is estimated to have a room-temperature bulk conductivity of 3.4 × 10^-11 S·cm^-1, an electrical activation energy of 0.9 eV, and a dielectric constant of 7.5. In this paper, impedance spectroscopy and X-ray powder diffraction were used to show the dependence of the electrical conductivity on the metal-metal bonding of pressed bulk powders of poly-[Rh(pdi)_4/2⁺(Cl)^-]. Thermo-gravimetric analysis and X-ray photoelectron spectroscopy were used to demonstrate air sensitivity in the polymer and elucidate the mechanism of oxidative degradation.