We report the first example of crystallographic observation of acetylene binding to -NO2 groups in a metal organic framework (MOF). Functionalization of MFM-102 with -NO2 groups on phenyl groups leads to a 15% reduction in BET surface area in MFM-102-NO2. However, this is coupled to a 28% increase in acetylene adsorption to 192 cm(3) g(-1) at 298 K and 1 bar, comparable to other leading porous materials. Neutron diffraction and inelastic scattering experiments reveal the role of -NO2 groups, in cooperation with open metal sites, in the binding of acetylene in MFM-102-NO2.