The metal organic framework material Cu3(BTC)2 (BTC = 1,3,5-benzenetricarboxylate) has been synthesized using different routes: under solvothermal conditions in an autoclave, under atmospheric pressure and reflux, and by electrochemical reaction. Although the compounds display similar structural properties as evident from the powder X-ray diffraction (XRD) patterns, they differ largely in specific surface area and total pore volume. Thermogravimetric and chemical analysis support the assumption that pore blocking due to trimesic acid and/or methyltributylammoniummethylsulfate (MTBS) which has been captured in the pore system during reaction is a major problem for the electrochemically synthesized samples. Isobutane and isobutene adsorption has been studied for all samples at different temperatures in order to check the potential of Cu3(BTC)2 for the separation of small hydrocarbons. While the isobutene adsorption isotherms are of type I according to the IUPAC classification, the shape of the isobutane isotherm is markedly different and closer to type V. Adsorption experiments at different temperatures show that a somewhat higher amount of isobutene is adsorbed as compared to isobutane. Nevertheless, the differential enthalpies of adsorption are only different by about 5 kJ/mol, indicating that a strong interaction between the copper centers and isobutene does not drive the observed differences in adsorption capacity. The calculated breakthrough curves of isobutene and isobutane reveal that a low pressure separation is preferred due to the peculiar shape of the isobutane adsorption isotherms. This has been confirmed by preliminary breakthrough experiments using an equimolar mixture of isobutane and isobutene.

The metal−organic framework (MOF) compound Cu3(BTC)2(H2O)3·xH2O (BTC = benzene 1,3,5-tricarboxylate) was prepared by solvothermal synthesis under ambient pressure and structurally characterized by powder X-ray diffraction and nitrogen adsorption at 77 K. X- and Q-band CW electron spin resonance and hyperfine sublevel correlation spectroscopies were used to explore the coordination state and location of the Cu(II) ions in the porous coordination polymer. Cupric ions were found to be present in two different chemical environments:  (a) Cu(II)2 clusters in the paddle-wheel building blocks of the Cu3(BTC)2 network, giving rise to an antiferromagnetically coupled spin state in accordance with previous susceptibility measurements (J. Appl. Phys. 2000, 87, 6007). However, the cross-linking of the paddle wheels by the BTC linker leads to an additional spin exchange among dimers as evidenced by the characteristics of the S = 1 ESR signal of their excited spin state. (b) In addition, paramagnetic monomer Cu(II) species are accommodated in the pore system of Cu3(BTC)2. They coordinate to adsorbed water molecules and form [Cu(H2O)6]2+ complexes, which are inhomogeneously distributed over the Cu3(BTC)2 pore system.

Lithium makes the difference: A simple strategy for the synthesis of lithium-doped porous metal-organic frameworks (MOFs) is developed (see structure; C black, O red, AlO(6) blue octahedra), thus paving the way for the facile preparation of lithium-doped MOFs. Moreover, the significant increase in hydrogen adsorption predicted by theoretical calculations is observed.

In the parent metal-organic framework Cu 3 (btc) 2 material the Cu(II) pairs in the paddle wheel building blocks of the framework give rise to an antiferromagnetic spin state with an electron spin resonance (ESR) silent S ) 0 ground state. The thermally excited S ) 1 state of the Cu(II) pairs can be observed for temperatures above 80 K by ESR spectroscopy but give rise to an exchanged narrowed resonance line preventing the exploration of any structural details in the environment of the paddle wheel units. However, magnetically diluted paramagnetic binuclear Cu-Zn clusters can be formed by substitution of Cu(II) ions by Zn(II) at low doping levels, as already known for zinc-doped copper acetate monohydrate. Indeed, ESR, hyperfine sublevel correlation spectroscopy (HYSCORE) and pulsed electron nuclear double resonance (ENDOR) verify the successful incorporation of zinc ions at cupric ion sites into the framework of the resulting Cu 3-x Zn x (btc) 2 coordination polymer. The formation of such paramagnetic binuclear Cu-Zn paddle wheel building blocks allows the investigation of the interaction between the Cu(II) ions and various adsorbates by advanced pulsed ESR methods with high accuracy. As a first example we present the adsorption of methanol over Cu 3-x Zn x (btc) 2 , which was found to coordinate directly to the Cu(II) ions via their open axial binding site.