COOP metal

Total DOS and B-C COOP curves for both the superconducting YNi2B2C and YNiBC are illustrated in Figure 7.7. Nonzero N(EF) values are consistent with metallic behavior, and the peak in the DOS near EF for... 

Figure 5 Crystal structure of CoOP (a) projection parallel to Pt atom chains (b) projection perpendicnlar to Pt atom chain (reproduced by permission from Molecular Metals , ed. W. E. Hatfield, NATO Conference Series VI, Materials Science, Plenum, New York, 1979, vol. 1, p. 378)...

Both CoOP and MgOP exist in the same orthorhombic structure with space group Cccm at an appropriately high temperature with little variation in unit cell dimensions.68,73 This structure for CoOP is shown in Figure 5 and contains linear chains of [Pt(C204)2]x units with dPt Pt of 2.85 A in the Mg2+ and 2.841 A in the Co2+ salts.73 The divalent metal ions are located between the planes containing the bis(oxalato)platinate ions and are coordinated to six water molecules with... 

The electrical conductivity of CoOP as a function of temperature is shown in Figure 6. Above room temperature the compound exhibits metallic behaviour but coincidental with the development of the superstructure the conductivity falls rapidly with decreasing temperature. Below 250 K CoOp behaves as a semiconductor with an activation energy of meV.74 The conduction has been shown to be frequency dependent below 250 K.75 Thermopower studies have also clearly demonstrated the changeover from metallic behaviour above 300 K. to semiconductor behaviour below 250 K.72 The behaviour of ZnOP is very similar to that of CoOp, with the phase transition from the Cccm to Pccn space group occurring at 278 K. Superstructure formation is complete by about 260 K.77... 

Investigations of multicentre electrochemical metalloprotein function including metalloenzyme function have also been brought to a level, where both direct and catalytic modes, and elements of molecular mechanisms can be addressed. The latter are, however, entangled by features such as composite electrochemistry, extremely complicated molecular interaction patterns when more than two metallic redox centres are involved, fragile surface enzyme preparations, and lack of structural surface characterization of the adsorbed metalloenzymes. In this respect, two-centre metalloproteins constitute interesting promising intermediates where the coop-erativity between the metallic redox centres can be accurately addressed with molecular resolution within reach. 

The replacement of main-group atoms in clusters by transition-metal atoms generates a richer structural chemistry superimposed on the cluster basics illustrated by the p-block systems. A logical question arises here. What would a one-dimensional material containing a transition metal look like Well, the d AOs will generate bands in a similar manner as the s and p orbitals. The major novelty will be the introduction of orbitals of 8 symmetry. Let s look at a hypothetical chain composed of equidistant Ni atoms (d = 2.5 A). The computed band structure, DOS and COOP are illustrated in Figure 6.14. The COs at k = 0 and ir/d arc drawn below. As a review of the previous section, we will reconstruct it starting from the Bloch functions associated with the nine Ni AOs. 

The COOP curve reflects the fact that the lowest parts of the 3s and 3p bands are bonding and their upper parts are antibonding. There are three valence electrons per A1 atom so the band is 3/8 filled with the electrons in COs of Al-Al bonding character. Note that all the bonding levels are occupied whereas all the antibonding ones are empty. This is a mark of stability. There is no band gap at the Fermi level, consistent with the fact that bulk A1 is metallic in character. 

D. Cossa and P. Courau, ICES Fifth round intercalibration for trace metals in seawater. Coop. Res. Rep., vol. 136, ICES, Copenhagen, Denmark (1986). 

The described method can be applied to d-metals. A schematic plot of the expected DOS and COOP is shown in Figure 2.28. 

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