Local Structure of CPO-27-Ni Metallorganic Framework upon Dehydration and Coordination of NO

Abstract

Coordination polymer Ni2(dhtp)(H2O)2·8H2O is a 3D network that maintains crystallinity and porosity after solvent removal. A mild thermal treatment in high vacuo at 393 K removes not only water physisorbed on the walls of the structure but also water directly coordinated to the Ni(II) sites. This procedure allows us to obtain a MOF material with honeycomb structure able to strongly coordinate NO. In this contribution the characterization of CPO-27-Ni in respect to structural (EXAFS compared to XRD), vibrational (IR and Raman) and electronic (UV, XANES, and luminescence) properties is described in the case of the as prepared sample, of the dehydrated sample and after NO interaction. NO is strongly bonded at the Ni(II) sites, forming a 1:1 adduct; its presence causes large modification of the vibrational and electronic properties of the material with respect to the dehydrated one. Quantitative data considering energetic aspects (microcalorimetric measurements) are also included. The ability of H2O molecules to slowly displace NO from the Ni(II) sites makes this material a promising candidate for NO delivery inside biological tissues.