The triple helix inside the large-pore aluminophosphate molecular sieve VPI-5

McCusker, Lynne B.; Baerlocher, Ch.; Jahn, E.; Bülow, Martin

doi:10.1016/0144-2449(91)80292-8

Cited by 240 publications

(129 citation statements)

References 11 publications

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“…An exception is the structure given by McCusker et a1. 21 in which aluminum atoms on one of the three crystallographic sites are coordinated by four framework oxygens agreement with the value for the dehydrated structures, but the a axis is too large and tends to go to the value for hydrated VPI- 5. This is partly explained by the net increase of the T-O distance due to the fact that the lengthening of the A M bond is larger than the decrease in the P-O distance.…”

Section: Resultssupporting

confidence: 63%

Modeling of AlPO4-8, VPI-5, and related structures

Man¹,

Santen²,

Vogt³

1992

J. Phys. Chem.

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(5) Magnussen, 0. M.; Hotlos, J.; Beitel, G.; Kolb, D. M.; Behm, R. J. J.(6) Szldarczyk, M.; Bockris, J. O.'M. J. Electrochem. Soc. 1990,137,452. (7) The structure and infrared spectrum of AlP04-8, the 18-ring aluminophosphate VPI-5, and related structures are simulated using atomistic potentials and a generalized valence force field. The various topologies theoretically possible for the VPI-5 structure indicate that hexagonal prisms and cubes in the structure increase its lattice energy, thus decreasing the plausibility of the structure. This is not the only energy-determining feature; the relative orientation of neighboring tetrahedra also has an effect. The calculated differences in lattice energy between the 14-ring structure AlP04-8, the 18-ring structure VPI-5, and a hypothetical 24-ring structure are mainly due to density differences; no direct effect of the ring size on the lattice energy has been observed. Both VPI-5 and AlPO4-8 show a shift of layers when their lattice energy is minimized by optimizing the crystallographic coordinates and unit cell parameters. The hypothetical 24-ring structure does not show such a shift. This is probably due to the flexibility of the 24-rings that can completely accommodate strains in the initial structure. This is also indicated by the large loss of symmetry of the structure. The simulated infrared spectra reproduce essential differences between the experimental spectra of AlP04-8 and VPI-5. The highest frequency modes, however, are calculated to be too high. Spectra calculated with the structures obtained by lattice energy minimization agree better with experiment than those calculated with experimental structures. This can be explained by the presence of more physically acceptable angles in the relaxed structures compared with the experimental structures. The calculated spectrum of the hypothetical 24-ring structure is clearly distinguishable from that of VPI-5.

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Section: Resultssupporting

confidence: 63%

Modeling of AlPO4-8, VPI-5, and related structures

Man¹,

Santen²,

Vogt³

1992

J. Phys. Chem.

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“…High-resolution powder diffraction patterns recorded with synchrotron radiation have allowed great advances in structure determination for materials of moderate complexity such as zeolites and aluminophosphates (McCusker, 1988(McCusker, , 1991. Of the structures in Table 2(a), that of VPI-5 (crystal 2) was determined by powder diffraction (McCusker, Baerlocher, Jahn & Bulow, 1991) before the single-crystal work was done. The singlecrystal data served to confirm the low-symmetry space group, and to give more detail on the water molecule positions.…”

Section: Comparisons With Powder Diffractionmentioning

confidence: 99%

Recording Diffraction Data for Structure Determination for Very Small Crystals

Harding¹

1996

J Synchrotron Rad

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An account is given of experiences in recording diffraction data with synchrotron radiation to determine structures for very small crystals, too small for use with conventional X-ray sources and diffractometers. The effect of crystal composition as well as size on the relative intensity of diffraction patterns of different crystals is noted. Crystal mounting is briefly described. Experimental methods are outlined including detectors and other instrumentation, and a range of examples is given; these include the use of both monochromatic area-detector systems for intensity measurement and of the white-beam Laue method. Choice of the shortest wavelength available with adequate intensity is recommended. The examples include organic, organometallic and aluminophosphate compounds; in all cases structure determination was important in relation to chemical research projects -they were not chosen as 'test' crystals. Comparison is made of the quality of the structure refinements achieved with those from synchrotron radiation powder diffraction -the alternative method when good-sized crystals are not available. Commonly it is found that when good-quality large crystals of a substance cannot be grown, the small crystals are poor in quality with substantial mosaic spread; the relationship between mosaic spread, structure, morphology and crystal growth is explored.

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“…Figure 5 shows the UV/ Vis spectra of 4 and 2, as well as their electrochemically oneelectron oxidized forms [4] . and [2] . .…”

mentioning

confidence: 97%

“…This is somewhat surprising, because in all known Cu II ± semiquinonate complexes this intramolecular exchange coupling is ferromagnetic, yielding an S 1 ground state. [2] What is the mechanism of the exchange coupling in GO?…”

mentioning

confidence: 99%

Why Does the Active Form of Galactose Oxidase Possess a Diamagnetic Ground State?

Müller

Weyhermüller

Bill

et al. 1998

Angewandte Chemie International Edition

100

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The relative orientation of the two magnetic orbitals, the Cu d x 2-y 2 orbital and the half-occupied π orbital of the tyrosyl radical, is the key to answering the question in the title. The arrangement shown (Cu -O-C bond angle of about 130° and a dihedral angle of about 90° between the x,y plane of the Cu polyhedron and the tyrosyl ring plane) leads to an overlap of the orbitals, which results in a singlet ground state.

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The triple helix inside the large-pore aluminophosphate molecular sieve VPI-5

Cited by 240 publications

References 11 publications

Modeling of AlPO4-8, VPI-5, and related structures

Modeling of AlPO4-8, VPI-5, and related structures

Recording Diffraction Data for Structure Determination for Very Small Crystals

Why Does the Active Form of Galactose Oxidase Possess a Diamagnetic Ground State?

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