The energy costs associated with large-scale industrial separation of light hydrocarbons by cryogenic distillation could potentially be lowered through development of selective solid adsorbents that operate at higher temperatures. We have recently found an iron-based metal organic framework that exhibits excellent performance characteristics for separation of acetylene/ethylene/ethane and propylene/propane mixtures at 318 K [Bloch et al, Science 2012 ]. Determination of the static structural properties of the framework/ coordinating adsorbate molecules, reveals a strong interaction of the Fe with the unsaturated bonds. The identification of a strongly bent H-C-C-H would indicate a very large enthalpy of interaction between the fe-acetylene, that needs to be confirmed through spectroscopy.