G. P. M. Van der Velden

Characterization of intermediate TPA-ZSM-5 type structures during crystallization

Abstract A wide range of analytical techniques (XRD, DTA/TGA, I.R., texture, SEM/TEM,13C,27Al,29Si MAS NMR) has been used to characterize intermediate products formed during the crystallization process of the zeolite Tetrapropylammonium ZSM-5 (TPA-ZSM-5). In the beginning of the crystallization process the solid products are XRD-amorphous and consist of an aluminum-rich phase next to an increasing amount of TPA-ZSM-5 entities with dimensions of the order of the unit cell of ZSM-5. In the final stage of the crystallization process (here up to 8 days) the TPA-ZSM-5 entities recombine to a crystalline ZSM-5 framework. A large amount of framework defects are then still present in the XRD-crystalline TPA-ZSM-5 framework as evidenced by 29Si MAS NMR. These defects disappear upon calcination.

The characterization of chemically modified silica gels by high-resolution solid-state 13C NMR

Abstract The power of solid-state 13C NMR for the characterization of chemisorbed surface species is demonstrated for a series of chemically modified silica gels. These materials find wide application in the fields of catalysis and separation science and the availability of a new tool for their routine investigation opens new possibilities for understanding processes which occur at surfaces.

A modulation technique for discriminating between homogeneous and inhomogeneous ODMR lines

Abstract A new technique is described which can be helpful in discriminating between homogeneously and inhomogeneously broadened optically detected magnetic resonance (ODMR) lines. The method has been applied to a number of single crystals. In the case of 1,5-dibenzoylnaphthalene a considerable homogeneous broadening was found.

Optical and magnetic properties of disubstituted benzophenones with lowest 3nπ* states

Abstract The phosphorescence and optically detected magnetic resonance (ODMR) spectra of 4,4′-dimethoxy-, 4,4′-dimethyl-,3,3′-dibromo- and 2,2′-diazaben have been measured. For 4,4′-dimethoxybenzophenone two X-traps have been found. The zero-field splitting (ZFS) parameters and the phosphorescence dec indicate that the lowest triplet states have mainly nπ* character, The effects of the substituents on the ZFS parameters cannot be explained via spin coupling with only nearby excited states.

Crystallographic and spectroscopic study on 4,4′-diiodobenzophenone

Abstract4,4′-Diiodobenzophenone crystallizes in the orthorhombic space groupCcc 2:a = 28.079,b = 7.413,c = 6.050Å,Z = 4. The structure has been determined by a combination of Patterson and direct methods with MoKα diffractometer data and refined by full-matrix least squares toR = 0.047 for 1512 reflections. The molecule possesses Crystallographic two-fold symmetry. The phosphorescence emission spectra of 4,4′-diiodobenzophenone are discussed in the light of structural data and spectroscopic data of several related benzophenones.

The lowest triplet state of 4,4′-diiodobenzophenone

Abstract From optically detected magnetic resonance experiments in zero magnetic field at 1.2 K, the zero-field splitting parameters, and iodine quadrupole and the iodine hyperfine interaction parameters are determined of the lowest triplet state of 4,4′-diiodobenzophenone, present as X-traps in single crystals of 4,4′-diiodobenzophenone. The addition of iodine to the benzophenone molecule greatly perturbs the zero-field splitting: compared to benzophenone and other dihalogen substituted benzophenones two triplet spin components have reversed their order. When we assume that the lowest triplet state of 4,4′-diiodobenzophenone is an 3 nπ* state, an assumption not in contradiction with our phosphorescence emission results, the reversal of two triplet spin components can be explained by second-order spin—orbit coupling involving iodine 5d π orbitals.