Dumbbell coordination

The mercury cuprates are diflScult to synthesize as pure phases, due to their low stability which originates form the dumbbell coordination of mercury. The difficulty in isolating pure phases increases with the number of copper layers. Moreover, only the barium layered cuprates HgBa2Ca jCu, 02m+2 are obtained, whereas the strontium homologous series could not be synthesized. The introduction of a rare earth into the Hg sites allows the anionic sites at the level of the Hg sites to be partially filled, and consequently the structure can be stabilized (for a review see Raveau et al. 1995a). 

Besides the oxide sulfate described above, (NH4)2[Pt2(S04)4(H20)2] is obtained in the reaction of Pt(N03)2 with concentrated sulfuric acid in sealed glass ampoules at 400 °C.124 In the crystal structure, Pt2 dumbbells are coordinated by four bidentate-bridging sulfate ions and two axial H20 molecules. The... 

For a-Ga (coordination number 1 + 2 + 2 + 2) the short Ga-Ga bond distance of 2.45 A of every Ga atom with one of its seven neighbors is characteristic, so that a-Ga is also described as a molecular metal with Ga2 dumbbells. For the low-temperature phases / -, y-, and r)-Ca the following characteristic units are observed the ladder structure (coordination number 2 + 2 + 2 + 2) for /i-gallium, Gayrings that stack to form tubes and a centered Ga wire , observed for y-Ga, and interpenetrating Gan icosahedra for b-Ga. 

It is interesting to examine the bead-spring models to see what flow-induced configurational changes would be required in order to develop N2 values of the proper magnitude and sign. In the Rouse model, the components of the stress tensor are related directly to averages of the internal coordinates of the beads. For the simplest case of the elastic dumbbell ... 

To explain why complexes are colored, we need to look at the effect of the ligand charges on the energies of the d orbitals. Recall that four of the d orbitals are shaped like a cloverleaf, and the fifth (d-/) is shaped like a dumbbell inside a donut (Section 5.8). Figure 20.28 shows the spatial orientation of the d orbitals with respect to an octahedral array of charged ligands located along the x, y, and z coordinate axes. 

All orbitals with a value of 1 = 1, are the orbitals of the p subshell. The p orbitals are not spherical. Each p subshell consists of three orbitals in the form of lobes that differ in their orientation. These lobes are separated from each other by a plane where the probability of finding the electron is zero. The lobes are located on both sides of this plane like a dumbbell. The shape of the p orbitals are the same but the directions of the lobes are different. Since it is possible to imagine that these lobes are oriented along x, y and z coordinates, so the corresponding p orbitals are denoted by px, py and pz. Hence, in all main energy levels, except first energy level (n = 1), there are three p orbitals. 

Fig. 26 Active template synthesis [185] (i) metal catalyst is bound in the cavity of a macrocycle, ( ) reagents (half-dumbbells in this example) coordinate the metal within the macrocycle, (Hi) a covalent bond is catalytically formed, resulting also in a mechanical bond, and (iv) catalyst is regenerated and the MIM is expelled...

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