The Raman band around 780-830 [cm.sup.-1] is corresponding to the vibrational modes of a regular Nb[O.sub.4] tetrahedron, and the band near 500-700 [cm.sup.-1] is assigned as the symmetric stretching mode of the Nb[O.sub.6] octahedra
[1, 18, 19].
On the relationship between the MOFs with different topology s, MIL-53(Al) with one rhombic-shaped pores has two kinds of adsorption sites, ethane and propane are preferential adsorbed at the energetic effect site which is near the AlO4(OH)2 octahedra
due to the strong vander hoff interactions between the framework and the longer alkanes, while methane with smaller size prefers to occupy the less energetical adsorption site arising from the space hindrance effect in the main channel.
Changes in surface area increase and the pore size distribution were dependent on the structure and leaching ability of cations from the interlayer and octahedra
. Dehydration of mixed-layer vermiculites were observed at the two endothermic effects.
In this way both face surfaces could be the same with alternating regions of silica tetrahedral and alumina octahedra
1991), and the octahedra
most likely pyrite, based on their distinctive morphology and elemental composition.
Here the alumina octahedra
replace all but two of their hydroxyl groups by sharing oxygen atoms with the silica sheets.
We soon learned that microscopic crystals of dry ice had already been observed as cubes, octahedra
, and cuboctahedra, so we felt ourselves on reasonably safe ground and proceeded with our quest.
This structure contains layers of a single P atom surrounded by six Cr[Se.sub.6] octahedra
in the ab plane, as pictured in Figure 2.
The thermodynamically stable form consists of 2 similar chains of Mo[O.sub.6] octahedra
aligned in ab configuration .
Thus the factors like Nb-O stretching, O-Nb-O bending, Ca-O stretching, and the vibrations involving chain bonds and the broadening of the peaks indicate a slightly distorted (Nb[O.sub.6] octahedra
) crystal structure.
[alpha]-[Al.sub.2] 14.16 Corundum--distorted [O.sub.3] octahedra
. Al-catechin complex 13.85 Al-complex with irregularly arranged phenolic molecules.
In dimension four, mathematicians have long had a prime candidate for the best kissing arrangement: the 24-cell, a perfectly symmetric shape with 24 comers and 24 three-dimensional sides that are all regular octahedra
. If one four-dimensional sphere is placed at each corner, these 24 spheres all kiss the central sphere.