Right-pyramidal structure

Fig. 3.15 Left External view of the MIMOS II sensor head (SH) with pyramid structure and contact ring assembly In front of the Instrument detector system. The diameter of the one Euro coin is 23 mm the outer diameter of the contact-ring is 30 mm, the inner diameter is 16 mm defining the field of view of the Instrument. Right. Mimos II SH (without contact plate assembly) with dust cover taken off to show the SH Interior. At the front, the end of the cylindrical collimator (with 4.5 mm diameter bore hole) Is surrounded by the four SI-PIN detectors that detect the radiation re-emltted by the sample. The metal case of the upper detector is opened to show its associated electronics. The electronics for all four detectors Is the same. The Mossbauer drive is inside (in the center) of this arrangement (see also Fig. 3.16), and the reference channel is located on the back side In the metal box shown In the photograph...

The sample studied was a cobalt bis(phosphonate) of composition C02(O3PC6H4OC6H4PO3)-2H2O. It is one of the series of first row transition element compounds with the same general formula, but different water contents. The Cu(ll) compound structure was solved from its powder pattern, unit cell dimensions a = 8 1012(5), b = 5.3109(3), c = 29.2595(5) A. It has a layered structure in which the layers are spaced at half the c-axis dimension. The reason for the doubling of the c-axis is that in one layer the rings are tilted around the ether oxygen to the left and in the next layer to the right. The Cu atoms are 5-coordinate with square pyramidal structure. 

Fig. 7. Structures of five-coordinate Cu2+ from first principles molecular dynamics. A Berry twist mechanism for the interconversion of the two structures is shown (from left to right) the reorientation of the main axis of a square pyramidal configuration by pseudo-rotations via a trigonal bipyramidal configuration. The grey atoms in the plane of the trigonal bipyramid are all candidates for becoming apical atoms in a square pyramid.

Figure 17. Alternative valence bond pictures of the catalyst-enamide adduct Only one of the four three center-four electron resonance structures is shown (far right). Electron withdrawing substituents prefer the basal position of the square pyramidal metallocyclopropane structure, while electron donating substituents prefer the axial position.

FIGURE 11 Steps in the conversion of an asymmetric phosphorane (top left) into its enantiomer (top right) by a Berry pseudorotation mechanism. In each step, labeled Kx), one of the three equatorial ligands (the pivot ligand x) remains equatorial and is at the apex of the square pyramid in the transition structure. 

Between the pyramids the surface is not in the final c(2x2) structural state, but shows a row structure parallel to the [100] and [010] directions, i.e. there are two domains of this structure (Fig. 9a). These row structures are also found on top of mostly the rectangular type pyramids (Fig. 10, right panel). The rows are made of three atomic rows, presumably Pt (see LDOS argument) with a local (100) symmetry, a square with one atom in the middle. The lateral distance of the atoms in direction of the rows is approximately 4 A. Occasionally one of the middle atoms is missing giving the rows a beaded appearance. This reconstruction seems to be an obvious way of the (001) surface to handle the Sn deficiency in the surface - quite different from the other two cases, (111) and... 

---