Orbital ordering, electronic conductivity

Similar to (SN)t in their one-dimenston.il conductivity properties arc the stacked columnar complexes typified by [Pl(CN)j i. These square planar ions adopt a closely spaced parallel arrangement, allowing for considerable interaction among the d i orbitals of the platinum atoms. These orbitals are normally filled with electrons, so in order to get a conduction band some oxidation (removal of electrons) must take place. This may be readily accomplished by adding a little elemental chlorine or bromine to the pure tetracyanoplatinate salt to get stoichiometries such as K-.[Pt(CN)jBr0, in which the platinum has an average oxidation state of +2.3. The oxidation may also be accomplished electrolytically. as in the preparation of Rbj(Pt(CN)4J(FHF)04 (Fig. 16.8). which has a short Pt—Pi separation. The Pt—Pt distance is only 280 pm. almost as short as that (bund in platinum metal itself (277 pm) and in oxidized platinum "pop complexes (270 to 278 pm see Chapter l5).4- Cold-bronze materials of this type were discovered as early as 1842. though they have been little understood until recent times. The complexes behave not only as one-dimensional conductors, but... 

Qualitative valence-bond (VB) descriptions of the electronic structures of molecules are often able to provide "primitive patterns of understanding" [1] of the origin of various molecular properties. In this chapter, we shall give consideration to VB structures for some molecular systems that involve four active-space orbitals. The discussion will include VB formulations of the electronic structures of isolated molecules, reaction mechanisms, and types of "metallic orbitals" that can be used in VB representations for electron conduction in metallic lithium. For the latter topic, the results of STO-6G VB calculations are reported in order to make a provisional comparison of two conduction mechanisms. 

Pauling has introduced a "metallic" orbital [54] in order to provide a VB representation for electron conduction in alkali metals. For lithium, this orbital is a 2pa AO, and use of it enables "bicovalent" VB structures such as... 

In brief, the polymeric systems must possess both an orbital system which allows charge-carriers to be mobile (Figure 16.1) and the charge-carriers (Figure 16.2) in order to show electronic conduction. A controlled variation of electrical conductivity over many orders of magnitude (Figure 16.3) has become possible via such doping reactions [10]. 

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