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Three magnesium based metal–organic frameworks, Mg3(3,5-PDC)3(DMF)3·DMF [1], Mg(3,5-PDC)(H2O)·(H2O) [3], and Mg4(3,5-PDC)4(DMF)2(H2O)2·2DMF·4.5H2O [4], and a 2-D coordination polymer, [Mg(3,5-PDC)(H2O)2] [2] [PDC = pyridinedicarboxylate], were synthesized using a combination of DMF, methanol, ethanol, and water. Compound 1[space group P21/n, a= 12.3475(5) Å, b= 11.1929(5) Å, c= 28.6734(12) Å, β = 98.8160(10)°, V= 3916.0(3) Å3] consists of a combination of isolated and corner-sharing magnesium octahedra connected by the organic linkers to form a 3-D network with a 12.2 Å × 4.6 Å 1-D channel. The channel contains coordinated and free DMF molecules. In compound 2[space group C2/c, a= 9.964(5) Å, b= 12.0694(6) Å, c= 7.2763(4) Å, β = 106.4970(6)°, V= 836.70(6) Å3], PDC connects isolated seven coordinated magnesium polyhedra into a layered structure. Compound 3[space group P6122, a= 11.479(1) Å, c= 14.735(3) Å, V= 1681.7(4) Å3] (previously reported) contains isolated magnesium octahedra connected by the organic linker with each other forming a 3D network. Compound 4[space group P21/c, a= 13.7442(14) Å, b= 14.2887(15) Å, c= 14.1178(14) Å, β = 104.912(2)°, V= 2679.2(5) Å3] also exhibits a 3D network based on isolated magnesium octahedra with square cavities containing both disordered DMF and water molecules. The structural topologies originate due to the variable coordination ability of solvent molecules with the metal center. Water molecules coordinate with the magnesium metal centers preferably over other polar solvents (DMF, methanol, ethanol) used to synthesize the coordination networks. Despite testing multiple desolvation routes, we were unable to measure BET surface areas greater than 51.9 m2/g for compound 1.

The compounds Tc2Cl4(PMe3)4and Tc2Br4(PMe3)4were formed from the reaction between (n-Bu4N)2Tc2X8(X = Cl, Br) and trimethylphosphine. The Tc(II) dinuclear species were characterized by single-crystal XRD, UV−visible spectroscopy, and cyclic voltammetry techniques, and the results are compared to those obtained from density functional theory and multiconfigurational (CASSCF/CASPT2) quantum chemical studies. The compound Tc2Cl4(PMe3)4crystallizes in the monoclinic space group C2/c[a= 17.9995(9) Å, b= 9.1821(5) Å, c= 17.0090(9) Å, β = 115.4530(10)°] and is isostructural to M2Cl4(PMe3)4(M = Re, Mo, W) and to Tc2Br4(PMe3)4. The metal−metal distance (2.1318(2) Å) is similar to the one found in Tc2Br4(PMe3)4(2.1316(5) Å). The calculated molecular structures of the ground states are in excellent agreement with the structures determined experimentally. Calculations of effective bond orders for Tc2X82−and Tc2X4(PMe3)4(X = Cl, Br) indicate stronger π bonds in the Tc24+core than in Tc26+core. The electronic spectra were recorded in benzene and show a series of low intensity bands in the range 10 000−26 000 cm−1. Assignment of the bands as well as computing their excitation energies and intensities were performed at both TD-DFT and CASSCF/CASPT2 levels of theory. Calculations predict that the lowest energy band corresponds to the δ* → σ* transition, the difference between calculated and experimental values being 228 cm−1for X = Cl and 866 cm−1for X = Br. The next bands are attributed to δ* → π*, δ → σ*, and δ → π* transitions. The cyclic voltammograms exhibit two reversible waves and indicate that Tc2Br4(PMe3)4exhibits more positive oxidation potentials than Tc2Cl4(PMe3)4.This phenomenon is discussed and ascribed to stronger metal (d) to halide (d) back bonding in the bromo complex. Further analysis indicates that Tc(II) dinuclear species containing π-acidic phosphines are more difficult to oxidize, and a correlation between oxidation potential and phosphine acidity was established.

A joint experimental and computational study of noble gas adsorption in the metal–organic framework (MOF) material HKUST-1 has been carried out. Using a standard gas adsorption analyzer fitted with a cryostat, isotherms were measured for Xe, Kr, Ar, and Ne at optimum temperatures for the determination of loading-dependent heats of adsorption using the Clausius–Clapeyron equation. Direct calorimetric measurements for Kr and Xe adsorption provide comparable heats of adsorption. A detailed analysis of the experimental data alongside complementary grand canonical Monte Carlo (GCMC) simulations led to the conclusion that the strongest binding for noble gases occurs in and around the small tetrahedral pockets and not at the accessible Cu(II) sites in the structure. Synchrotron X-ray and neutron powder diffraction experiments with in situ gas loading confirm the assignment of preferred binding sites inferred from the adsorption measurements and simulations.