Graphene inclusion controlling conductivity and gas sorption of metal-organic framework

A general approach to prepare composite films of metal–organic frameworks and graphene has been developed. Films of copper(ii)-based HKUST-1 and HKUST-1/graphene composites were grown solvothermally on glassy carbon electrodes. The films were chemically tethered to the substrate by diazonium electrografting resulting in a large electrode coverage and good stability in solution for electrochemical studies. HKUST-1 has poor electrical conductivity, but we demonstrate that the addition of graphene to HKUST-1 partially restores the electrochemical activity of the electrodes. The enhanced activity, however, does not result in copper(ii) to copper(i) reduction in HKUST-1 at negative potentials. The materials were characterised in-depth: microscopy and grazing incidence X-ray diffraction demonstrate uniform films of crystalline HKUST-1, and Raman spectroscopy reveals that graphene is homogeneously distributed in the films. Gas sorption studies show that both HKUST-1 and HKUST-1/graphene have a large CO(2)/N(2) selectivity, but the composite has a lower surface area and CO(2) adsorption capacity in comparison with HKUST-1, while CO(2) binds stronger to the composite at low pressures. Electron paramagnetic resonance spectroscopy reveals that both monomeric and dimeric copper units are present in the materials, and that the two materials behave differently upon hydration, i.e. HKUST-1/graphene reacts slower by interaction with water. The changed gas/vapour sorption properties and the improved electrochemical activity are two independent consequences of combining graphene with HKUST-1

A Mononuclear Fe(III) Single Molecule Magnet with a 3/2↔5/2 Spin Crossover

The air stable complex [(PNP)FeCl(2)] (1) (PNP = N[2-P(CHMe(2))(2)-4-methylphenyl](2)(−)), prepared from one-electron oxidation of [(PNP)FeCl] with ClCPh(3), displays an unusual S = 3/2 to S = 5/2 transition above 80 K as inferred by the dc SQUID magnetic susceptibility measurement. The ac SQUID magnetization data, at zero field and between frequencies 10 and 1042 Hz, clearly reveals complex 1 to undergo a frequency dependent of the out-of-phase signal and thus be a single molecular magnet with a thermally activated barrier of U(eff) = 32-36 cm(−1) (47 - 52 K). Variable temperature Mössbauer data also corroborate a significant temperature dependence in δ and ΔE(Q) values for 1, which is in agreement with the system undergoing a change in spin state. Likewise, variable temperature X-band EPR spectra of 1 reveals the S = 3/2 to be likely the ground state with the S = 5/2 being close in energy. Multi-edge XAS absorption spectra suggest the electronic structure of 1 to be highly covalent with an effective iron oxidation state that is more reduced than the typical ferric complexes due to the significant interaction of the phosphine groups in PNP and Cl ligands with iron. A variable temperature single crystal X-ray diffraction study of 1 collected between 30-300 K also reveals elongation of the Fe–P bond lengths and increment in the Cl–Fe–Cl angle as the S = 5/2 state is populated. Theoretical studies show overall similar orbital pictures except for the d(z(2)) orbital which is the most sensitivity to change in the geometry and bonding where the quartet ((4)B) and the sextet ((6)A) states are close in energy