Sensitive and selective chromogenic sensing of carbon monoxide via reversible axial CO coordination in binuclear rhodium complexes

Abstract

The study of probes for CO sensing of a family of binuclear rhodium(II) compounds of general formula [Rh2{(XC6H3)P(XC6H4)}n(O2CR)4-n] · L2 containing one or two metalated phosphines (in a head-to-tail arrangement) and different axial ligands has been conducted. The binuclear rhodium complexes were adsorbed on silica and used as colorimetric probes for “naked eye” CO detection in the gas phase. When the gray-purple colored silica solids containing the rhodium probes were exposed to air containing increasing concentrations of CO, two colors were observed, in agreement with the formation of two different products. The results are consistent with an axial coordination of the CO molecule in one axial position (pink-orange) or in both (yellow). In all cases, the binuclear rhodium complexes studied showed a high selective response to CO with a remarkable low detection limit. Furthermore, the binding of CO in these rhodium complexes was found to be fully reversible.