Sixth main group elements

Materials for PC Media. Crystalline alloys of elements from the fifth and sixth main group are preferred (3,103,109—111). As the first PC materials, tellurium suboxides as well as Te/Se or Te films that had been doped with small amounts of other elements like Ge, As, or Sb to shift the crystallization point to >100°C have been described. 

The molecules in crystalline chlorine, bromine and iodine are packed in a different manner, as shown in Fig. 11.1. The rather different distances between atoms of adjacent molecules are remarkable. If we take the van der Waals distance, such as observed in organic and inorganic molecular compounds, as reference, then some of the intermolecular contacts in the b-c plane are shorter, whereas they are longer to the molecules of the next plane. We thus observe a certain degree of association of the halogen molecules within the b-c plane (dotted in Fig. 11.1, top left). This association increases from chlorine to iodine. The weaker attractive forces between the planes show up in the plate-like habit of the crystals and in their easy cleavage parallel to the layers. Similar association tendencies are also observed for the heavier elements of the fifth and sixth main groups. 

The layer and chain structures of the elements of the fifth and sixth main groups result by contraction of certain distances in the a-Po structure (stereo images)... 

Elements of the Fifth and Sixth Main Groups underpressure... 

Crystal structure determinations from very small samples have become possible due to the high intensities of the X-rays from a synchrotron. Very high pressures can be exerted on a small sample situated between two anvils made from diamond. In this way, our knowledge of the behavior of matter under high pressures has been widened considerably. Under pressure the elements of the fifth and sixth main groups exhibit rather unusual structures. A synopsis of the structures that occur is given in Fig. 11.9. 

Reaction with Elements of the Sixth Main Group... 

Accurate Relativistic Effective Potentials for the Sixth-Row Main Group Elements. 

During the introduction of this review, reference was made to the classical rule of the double bond. The theory, which in its original predictions supports the exceptional position for the elements boron, carbon, nitrogen, and oxygen, has lost its validity and needs modifications, as can be seen from the erratic increase in the numbers of compounds that contradict the rule that have been discovered within the last 12 years. These compounds are not found only as low-valent phosphorus-carbon species, but also increasingly as heteronuclear and even homonuclear molecules built up by heavier elements of the fourth to sixth main groups, such as Si, Ge, As, Sb, S, and Se. 

We shall not discuss the electron configurations of all the elements in the fifth and sixth periods, but be content to point out that the ground state electron configurations of all main group elements in Groups 1, 2 and from 12 to 18 are in accord with the aufbau model. 

S. A. 1451dman, G. A. LMLabio, P. A. Christiansen. Accurate relativistic effective potentials for the sixth-row main group elements. J. Chem. Phys., 107 (1997) 9975-9979. 

All reactions with XeF MF5" (M = As, Sb) mentioned so far for elements of the fifth and sixth main group have been examples of either oxidative fluorination forming E-F cations or the synthesis of a transition state with an E-XeF+ structural unit. It seemed logical to extend our investigations to the elements of the seventh main group in order to prepare Hal2F or possibly Hal2XeF salts. However, the analytical and... 

Figure 2 Configuration energie.s (eV) for the 45 main group elements (H to Rn). Filled in circles are sixth-row elements...

The 7 periods (horizontal rows) and 18 groups (vertical columns) of the periodic table. Note that not all periods contain the same number of elements. Also note that, for reasons explained later, the sixth and seventh periods each include a subset of elements, which are listed apart from the main body. 

As explained in the Preface, the organization of this sixth edition does not include chapters on broad classes of compounds (e.g., organometallic compounds) nor on broad topics (e.g., bioinorganic chemistry). Much material that previously appeared in such chapters is now distributed in the present rewritten chapters on the chemistry of individual elements or groups of elements. However, there are still cross-cutting concepts that are best treated generically. That will be done partly in this chapter, but also, for a few topics that are mainly relevant to transition metal chemistry, in Chapter 16. 

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