Chalcogenides 1152 preparation

The most important mercury chalcogenide halides are of the type HgaYjXj (Y = S, Se, Te X = Cl, Br, I). The corresponding sulfide halides have been known for over 150 years (326). Quite a lot of work has been performed concerning the preparation, structures, electronic and optical properties, and phototropic behavior of these compounds. Mercury chalcogenide halides of other compositions have been mentioned in the literature (141). As most of these compounds are not well established, they will not be treated in detail, with the exception of the latest contributions (see Table V). 

The phototropic behavior of the mercury chalcogenide halides has received particular attention. This interest was stimulated by the hope that these materials might allow the preparation of photolayers capable of repeated use for the production of images. 

Fig. 16. Preparation of lanthanide chalcogenide halides experimental arrangement.

Just as, in Group VB, niobium, so, in this Group, molybdenum provides most of the examples of the chalcogenide halides. The occurrence and preparation of such compounds are described in numerous publications. In most cases, they have been obtained as powders, with the composition based on chemical analyses only. The presence of defined, homogeneous phases is, therefore, in many cases doubtful. In addition, some published results are contradictory. A decision is possible where a complete structure analysis has been made. As will be shown later, the formation of metal-metal bonds (so-called clusters), as in the case of niobium, is the most characteristic building-principle. Such clusters... 

In this section, a review is given of preparative work on chalcogenide halides. Table XIII summarizes the proposed compositions thus far described in the literature. 

Preparative Routes and Experimental Conditions for the Formation OF Rhenium Chalcogenide Halides... 

Thiele and co-workers 389) prepared the only known palladium chalcogenide halides, PdTel and Pd Sels, by hydrothermal synthesis in HI (see Section II,D,2) at 300°C, starting with the elements. Crystalline PdzSelj is better obtained by reaction of Pdl2 with Se and an excess of iodine in a closed ampoule at 250°C (reaction time, 2 days). 

Thiele and co-workers, who tried to prepare platinum chalcogenide halides, could neither isolate nor identify any pure, homogeneous compound (389). 

The compounds AlYX are best prepared by direct reaction between the respective aluminum halide and chalcogenide in a sealed ampoule at 350°C. The reaction is complete after 2 weeks. In the case of the iodides, a mixture of A1 and I2 (molar ratio 3 10) is used instead of AII3. Other preparative methods, such as the reaction of an aluminum halide with Zn or Cd chalcogenide, or with the chalcogen itself, are applicable to the bromide and chloride only, and give poor yields (15-20%) (158, 159, 266, 327, 328). 

The chalcogenide bromides and chlorides may be prepared by the reaction of the halide with the respective chalcogenide in a sealed ampoule. A mixture of gallium metal and chalcogen may be used, instead of the chalcogenide. The chalcogenide iodides are S3mthesized directly from the elements. The exact preparative conditions are listed in Table XVIII 160,165). 

Indium chalcogenide chlorides and bromides are obtained by heating mixtures of the chalcogenide and the halide in sealed ampoules to temperatures between 200 and 420°C (see Table XIX). For the preparation of the chalcogenide iodides. In and I2 are used instead of Inlj. InTel may be synthesized directly from the elements (161). 

The binary chalcogenides of antimony and bismuth are highly colored compounds that are readily prepared by direct reaction of the elements at 500-900 C. They have rather complex ribbon or layer structures and exhibit semiconductor properties. 

The electrochemical preparation of metal chalcogenide compounds has been demonstrated by numerous research groups and reviewed in a number of publications [ 1-3]. For the most part, the methods that have been used comprise (a) cathodic co-reduction of the metal ion and a chalcogen oxoanion in aqueous solution onto an inert substrate (b) cathodic deposition from a solvent containing metal ions and the chalcogen in elemental form (the chalcogens are not soluble in water under normal conditions, so these reactions are carried out in non-aqueous solvents) (c) anodic oxidation of the parent metal in a chalconide-containing aqueous electrolyte. 

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