Transition-metal arsenides

Transition-Metal Arsenides, MAs, and Mixed Arsenide Phosphides, MAsi yPy... 

Among binary transition-metal pnictides, only the first-row transition-metal phosphides have been analysed by XPS extensively, whereas arsenides and antimonides have been barely studied [51-61]. Table 2 reveals some general trends in the P 2p3/2 BEs for various first-row transition-metal monophosphides, as well as some metaland phosphorus-rich members forming for a given transition metal. Deviations of as much as a few tenths of an electron volt are seen in the BEs for some compounds measured multiple times by different investigators (e.g., MnP), but these... 

Several transition metal sulfides (e.g., FeS, CoS, and NiS) adopt a structure called the nickel arsenide structure, illustrated in Fig. 12-4. In this structure each metal atom is surrounded octahedrally by six sulfur atoms, but also is approached... 

It is more difficult to prepare III-V semiconductors than the II-VI. Two sonochemical investigations reported on the preparation of these materials. The first paper details a safe method for the preparation of transition metal arsenides, FeAs, NiAs, and CoAs [142]. At room temperature, well-crystallized and monodispersed arsenide particles were successfully obtained under high-intensity ultrasonic irradiation for 4 h from the reaction of transition metal chlorides (FeCla, NiCl2, and C0CI2), arsenic (which is the least toxic arsenic feedstock) and zinc in ethanol. Different characterization techniques show that the product powders consist of nanosize particles. The ultrasonic irradiation and the solvent are both important in the formation of the product. 

The phosphides and arsenides of the elements M—PRR and M—AsRR are well known for main group elements, but transition metal analogues are more unusual. Insertion reactions were not widely explored until recently, but examples are given in reactions (j) and (k) (X = O or S) ° and (l) (n) (X = or As ) and (m) are effectively oxidative insertions of a nitrene, or specifically PhN into an Sn-P or Sn-As bond, and thus represent an extension of the Staudinger reactions whereby a phosphine or arsine is treated with an azide, and thereby converted into a phosphine-imine or the arsine analogue, as follows ... 

The nickel arsenide structure. The structure most frequently encountered is the NiAs structure (Fig. 17.1), which is also that of many phases MX in which M is a transition metal and X comes from one of the later B subgroups (Sn, As, Sb, Bi, S,... 

The A2 metals and the elements of the earlier B subgroups (Bj metals) form the electron compounds already discussed. With the metals of the later B subgroups the A2 metals, like the Aj, tend to form intermetallic phases more akin to simple homopolar compounds, with structures quite different from those of the pure metals. The nickel arsenide structure has, like typical alloys, the property of taking up in solid solution a considerable excess of the transition metal. From Table 29.12... 

Solid chalcogenides are formed by all metallic elements and by many nonmetals. Only with the most electropositive metals do they commonly have the same structures as oxides (see Topics D3 and D4). With transition metals, compounds MX (which are frequently of variable stoichiometry) have the nickel arsenide or similar structures in which metal-metal bonding is present. MX2... 

The nickel arsenide structure occurs not only in the sulphides but also in many other compounds containing a transition metal and one of the elements Sn, Pb, As, Sb, Bi, Se and Te. Many of these systems are essentially intermetallic in their properties and will be discussed further in the chapter devoted to alloys. Here, however, it is interesting to note that as the system becomes more metallic so the bonding in the vertical direction becomes stronger. Thus in FeS the Fe-S and Fe-Fe distances... 

Transition metals may also interfere in ionic form in solutions at high concentrations. It has been concluded that after its formation the hydride will react at the gas/liquid phase boundary with free interfering metal ions in the acidified sample solution giving insoluble arsenides, selenides, tellurides, etc. 

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