Fredrik Lundvall

In-situ flow MAS NMR and synchrotron PDF analyses of the local response of the Brønsted acidic site in SAPO-34 during hydration at elevated temperatures

In situ flow magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy and synchrotron-based pair distribution function (PDF) analyses were applied to study waters interactions with the Brønsted acidic site and the surrounding framework in the SAPO-34 catalyst at temperatures up to 300 °C for NMR spectroscopy and 700 °C for PDF. 29 Si enrichment of the sample enabled detailed NMR spectroscopy investigations of the T-atom generating the Brønsted site. By NMR spectroscopy, we observed dehydration above 100 °C and a coalescence of Si peaks due to local framework adjustments. Towards 300 °C, the NMR spectroscopy data indicated highly mobile acidic protons. In situ total X-ray scattering measurements analyzed by PDF showed clear changes in the Al local environment in the 250-300 °C region, as the Al-O bond lengths showed a sudden change. This fell within the same temperature range as the increased Brønsted proton mobility. We suggest that the active site in this catalyst under industrial conditions comprises not only the Brønsted proton but also SiO4 . To the best of our knowledge, this is the first work proposing a structural model of a SAPO catalyst by atomic PDF analysis. The combination of synchrotron PDF analysis with in situ NMR spectroscopy is promising in revealing the dynamic features of a working catalyst.

4,4′-Dimeth­oxybi­phenyl-3,3′-di­car­box­ylic acid

The title compound, C16H14O6, was recrystallized under solvothermal conditions. The molecules are located on inversion centres, with one complete molecule generated from the asymmetric unit by inversion. There are intramolecular O—H⋯O hydrogen bonds involving the carboxylic acid group and the O atom of the adjacent methoxy group. In the crystal, molecules are linked via O—H⋯O hydrogen bonds, forming chains propagating along [100]. The chains are linked via C—H⋯O hydrogen bonds, forming sheets parallel to (001).

SAPO-37 microporous catalysts: revealing the structural transformations during template removal

Abstract We have studied the structural behavior of SAPO-37 during calcination using simultaneous in situ powder X-ray diffraction (PXRD) and mass spectroscopy (MS) in addition to ex situ thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). A spike in the unit cell volume corresponding to template removal (tracked using the occupancy of the crystallographic sites in the SAPO-37 cages) is revealed from the XRD data and is strongly correlated with the DSC curve. The occupancy of the different template molecules in the faujasite (FAU) and sodalite (SOD) cages is strongly related to the two mass loss steps observed in the TGA data. The templates act as a physical stabilizing agent, not allowing any substantial unit cell response to temperature changes until they are removed. The FAU cages and SOD cages have different thermal response to the combustion of each template. The FAU cages are mainly responsible for the unit cell volume expansion observed after the template combustion. This expansion seems to be related with residual coke from template combustion. We could differentiate between the thermal response of oxygen and T-atoms. The T–O–T angle between two double 6-rings and a neighboring T–O–T linkage shared by SOD and FAU had different response to the thermal events. We were able to monitor the changes in the positions of oxygen and T-atoms during the removal of TPA+ and TMA+. Large changes to the framework structure at the point of template removal may have a significant effect on the long-term stability of the material in its activated form.

Ab initio structure solution and thermal stability evaluation of a new Ca(II) 3D coordination polymer using synchrotron powder X-ray diffraction data

A new coordination polymer was synthesized hydrothermally using 4,4′-dimethoxy-3,3′-biphenyldicarboxylic acid (H2dmbpdc) and Ca(NO3)2·4H2O. The structure of the new compound, Ca(dmbpdc)(H2O)2 (CPO-70-Ca), was determined from powder X-ray diffraction (PXRD) data using simulated annealing, followed by Rietveld refinement of the structure. The framework is based on one-dimensional metal carboxylate chains that are linked by the organic linker into a three-dimensional network with rhombic channels. The as-synthesized material resembles our recently reported compound CPO-69-Ca, and shares the same sra topology. The asymmetric unit comprises one calcium atom, one fully deprotonated linker, one water molecule coordinated to the metal cation as well as one solvent water molecule located in the rhombic channels. The metal cation is eight-coordinate, forming an irregular coordination polyhedron. The thermal behavior of CPO-70-Ca was investigated in an in situ structural analysis by variable temperature powder X-ray diffraction. This study revealed an interesting response to solvent removal from the as-synthesized structure. The results include a partially desolvated version of CPO-70-Ca and a structural transformation to CPO-69-Ca upon full desolvation.

Crystal structure of catena-poly[[[aqua­bis­(di­methyl­formamide-κO)magnesium(II)]-μ3-(2,2′-bi­pyridine-5,5′-di­carboxyl­ato-κ5O2:O2′:N,N′:O5)-[di­chlorido­platinum(II)]] di­methyl­formamide monosolvate]

A new one-dimensional coordination polymer formed unexpectedly during the synthesis of a Pt-functionalized bipyridine linker for metal–organic frameworks. We report here the synthesis, structure determination and energy-dispersive X-ray spectroscopy analysis of this new coordination polymer.

Crystal structure of dimethyl 4,4′-di­meth­oxy­biphenyl-3,3′-di­carboxyl­ate

The title compound is an intermediate in the synthesis of linkers for coordination polymers. Centrosymmetric molecules are packed along the a axis to form corrugated layers parallel to the ac plane.

Methyl 5-iodo-2-meth-oxy-benzoate.

In the title compound, C9H9IO3, the molecules are close to planar [maximum deviation from benzene ring plane = 0.229 (5) Å for the methyl carboxylate C atom] with the methyl groups oriented away from each other. In the crystal, molecules form stacked layers parallel to the ab plane, where every layer has either the iodine or methoxy/methyl carboxylate substituents pointing towards each other in an alternating fashion.

Dimethyl 3,3′-dimethoxybiphenyl-4,4′-dicarboxylate

In the title compound, C18H18O6, the biphenyl moiety is twisted with a dihedral angle of 29.11 (10)°. The carbomethoxy groups form C—C—C—O torsion angles of −18.3 (3) and −27.7 (3)° with the attached rings, as a result of steric hindrances from the nearby methoxy groups. In the absence of stacking interactions and with no H⋯O contacts shorter than 2.7 Å, the packing is dominated by weaker van der Waals interactions.

(E)-9-(But-2-en-1-yl)-6-chloro-9H-purine

The asymmetric unit of the title compound, C9H9ClN4, contains two molecules. In the crystal, the molecules are ordered in a chain-like fashion along the a axis, and form layers offset relative to the C plane by approximately 30°. This ordering does not, however, appear to be directed by classical hydrogen bonding.The allylic side chains of both independent molecules are disordered, with occupancies of 0.870 (4) and 0.934 (3) for the major components. The disorder components represent two possible spatial orientations of the atoms around the C=C double bond.

(5,5'-Dimethyl-2,2'-bipyridine)-iodido-trimethyl-platinum(IV).

In the title compound, [Pt(CH3)3I(C12H12N2)], the PtIV atom is six-coordinated in a slightly distorted octahedral configuration with one CH3 group and the I atom forming a near perpendicular axis relative to the square plane formed by the bipyridine ligand and the two remaining CH3 groups. The CH3 group trans to the I atom has a slightly elongated bond to Pt compared to the other CH3 groups, indicating a difference in trans influence between iodine and the bipyridine ligand.