ID molecular metals

In MOMs dimensionality is a major issue. As discussed back in Chapter 1, although all materials are structurally 3D, some of them exhibit physical properties with lower dimensionality, ID or 2D, mainly due to the pseudo-planar conformation of the molecules. In fact for bulk materials one cannot strictly use the terms ID or 2D because intermolecular interactions build anisotropic but indeed 3D networks. Hence, one is led to using the prehxes pseudo or quasi when referring to ID or 2D systems. However, ideal ID and 2D systems can be artihcially prepared exhibiting real ID and 2D properties, respectively, and we will hnd some examples of this in the next sections. 

Since the gold chains are located at the surface of the sample, the wave vectors of the electronic states linked to the chains lie in the surface plane. This wave vector, 11 = sin is strictly conserved in the photoemission measurements. 

The spectra from Fig. 6.1(a) show a band approaching and finally crossing it, demonstrating the metallic character. It is important to notice that no emission from the substrate can be observed at E because the substrate is semiconducting. 

The suppression of the photoemission signal at in inorganic quasi-ID metals 

With these advisory ideas in mind let us spend some time on the electronic structure of one of the most extensively studied MOMs the quasi-ID metal TTF-TCNQ. 

---

We outline the application to an octahedral id transition metal complex, as the relations derived in this case are used to interpret the results of spin density measurements (see Sections VI. A and VI. B). A similar approach may be used for other coordinations and for other metals. Some general consequences relating the symmetry properties of complexes and a molecular orbital model of bonding have been combined in the angular overlap model< >... 

The diffusion current Id depends upon several factors, such as temperature, the viscosity of the medium, the composition of the base electrolyte, the molecular or ionic state of the electro-active species, the dimensions of the capillary, and the pressure on the dropping mercury. The temperature coefficient is about 1.5-2 per cent °C 1 precise measurements of the diffusion current require temperature control to about 0.2 °C, which is generally achieved by immersing the cell in a water thermostat (preferably at 25 °C). A metal ion complex usually yields a different diffusion current from the simple (hydrated) metal ion. The drop time t depends largely upon the pressure on the dropping mercury and to a smaller extent upon the interfacial tension at the mercury-solution interface the latter is dependent upon the potential of the electrode. Fortunately t appears only as the sixth root in the Ilkovib equation, so that variation in this quantity will have a relatively small effect upon the diffusion current. The product m2/3 t1/6 is important because it permits results with different capillaries under otherwise identical conditions to be compared the ratio of the diffusion currents is simply the ratio of the m2/3 r1/6 values. 

As mentioned before, we shall use small molecules to introduce the fundamentals for more complex molecules, the real core of this book, which will be listed in the next section. Such molecules form solids with remarkable properties (metallicity, superconductivity, ferromagnetism, etc.), some of them at ambient conditions or at much lower hydrostatic pressures than those found for H2 and N2, and some technological applications have been already developed, deserving the name of functional materials. Most of the molecules studied in this book are planar, or nearly planar, which means that the synthesized materials reveal a strong 2D structural character, although the physical properties can be strongly ID, and because of this 2D distribution we shall study surfaces and interfaces in detail. In particular, interfaces play a crucial role in the intrinsic properties of crystalline molecular organic materials and Chapter 4 is devoted to them. 

---