Electronic Structure, Pore Size Distribution, And Sorption Characterization Of An Unusual Mof, {[Ni(Dpbz)][Ni(Cn)(4)]}(N), Dpbz=1,4-Bis(4-Pyridyl)Benzene

The monoclinic (Ni(L)[Ni(CN)(4)] (L= 1,4-Bis(4-pyridyl) benzene) compound (defined as Ni-dpbz) is a flexible metal organic framework which assumes a pillared structure with layers defined by 2D Ni[Ni(CN)(4)](n) nets and dpbz ligands as pillars. The structure features an entrapped dpbz ligand that links between the open ends of four-fold Ni sites from two neighboring chains. This arrangement results in an unusual 5-fold pseudo square-pyramid environment for Ni and a significantly long NiN distance of 2.369(4) angstrom. Using Density Functional Theory calculations, the different bonding characteristics between the 5-fold and 6-fold Ni's were determined. We found that there is weak covalent bonding between the 5-fold Ni and N in the entrapped ligand, and the 6-fold Ni-N bonds provide effective electronic conduction. The disordered dimethyl sulfoxide (DMSO) solvent molecules are not bonded to the framework. The material has a single pore with a diameter of 4.1 angstrom. This pore includes approximately 55% of the total free volume (based on a zero-diameter probe). The accessible pore surface area and pore volume were calculated to be 507 m(2)/g and 6.99 cm(3)/kg, respectively. The maximum amount of CO2 that can be accommodated in the pores after DMSO is removed was found to be 204 mg/g, agreeing with the results of adsorption/desorption experiments of about 220 mg/g.