Phosphides structures

Compounds with Sc, Y, lanthanoids and actinoids are of three types. Those with composition ME have the (6-coordinated) NaCl structure, whereas M3E4 (and sometimes M4E3) adopt the body-centred thorium phosphide structure (Th3P4) with 8-coordinated M, and ME2 are like ThAsi in which each Th has 9 As neighbours. Most of these compounds are metallic and those of uranium are magnetically ordered. Full details of the structures and properties of the several hundred other transition metal-Group 15 element compounds fall outside the scope of this treatment, but three particularly important structure types should be mentioned because of their widespread occurrence and relation to other structure types, namely C0AS3,... 

With the small cations Mg+2 and Mn+2, Dy2S3 does not give any phase with the thorium phosphide structure. Calcium sulfide, on the other hand, yields phases with this structure with Dy2S3 and Y2S3 but not with Er2S3 (maximum value of Ra = 0.94). 

The presence of small quantities of metal phosphides can often profoundly affect the performance of metals, however, and this is sometimes pnt to nse in metallurgy. The fragmentary P units found in some metal phosphide structures are proving to be useful as building blocks in the synthesis of complex carbo and aza-phosphorus componnds. 

However, the densest of all phosphorus compounds are found amongst the metal phosphides (Table 8.4). These high densities arise from the presence of the heavy metal atoms and the efficiency with which they can pack with the phosphorus atoms in the crystal lattice. A simple but highly symmetrical scheme of coordination of both the metal atoms and the phosphorus atoms is found in many phosphide structures (see below). 

Three hypothetical ternary structures of the R/T, M), c family derived from known binary transition metal boride and phosphide structure types. 

The first part of this section is concerned with the crystal structures of ternary and quaternary phosphides and the isothermal sections of ternary systems. Systems R-M-P are considered in order of increasing atomic number of rare earth and then transition metal. The crystallographic characteristics of the phosphides are listed in tables. For phosphide structures which have been refined by single-crystal methods, atomic parameters and if-values are given. Compounds in each system are considered in order of increasing phosphorus and then rare-earth content. A separate column in the table indicates the method used for preparing the phosphide. 

A completely different structural motif has very recently been found in the red-brown phosphide CasPg, formed by direct fusion of Ca metal and red P in the correct atom ratio in a corundum crucible at 1000 C. The structure comprises Ca + cations and Pg anions, the latter adopting a staggered ethane conformation. (Note that P+ is isolobal with C and P with H so that C2H6 = [(P+)2(P"")6] = Ps - -) The internal P-P distance is 230.1pm and the terminal P-P distances 214.9-216.9 pm, while the internal PPP angles are 104.2-106.4° and the outer angles are 103.4-103.7°. 

Write the complete Lewis structure for each of the following compounds (a) ammonium chloride (b) potassium phosphide (c) sodium hypochlorite. 

In accordance with the electropositive nature of the bridgehead atoms, all di(pyridyl) substituted anions behave like amides with the electron density accumulated at the ring nitrogen atoms rather than carbanions, phosphides or arsenides. The divalent bridging atoms (N, P, As) in the related complexes should in principle be able to coordinate either one or even two further Lewis acidic metals to form heterobimetallic derivatives. According to the mesomeric structures, (Scheme 7), it can act as a 2e- or even a 4e-donor. However, theoretical calculations, supported by experiments, have shown that while in the amides (E = N) the amido nitrogen does function as... 

The structure of MnP is a distorted variant of the NiAs type the metal atoms also have close contacts with each other in zigzag lines parallel to the a-b plane, which amounts to a total of four close metal atoms (Fig. 17.5). Simultaneously, the P atoms have moved up to a zigzag line this can be interpreted as a (P-) chain in the same manner as in Zintl phases. In NiP the distortion is different, allowing for the presence of P2 pairs (P ). These distortions are to be taken as Peierls distortions. Calculations of the electronic band structures can be summarized in short 9-10 valence electrons per metal atom favor the NiAs structure, 11-14 the MnP structure, and more than 14 the NiP structure (phosphorus contributes 5 valence electrons per metal atom) this is valid for phosphides. Arsenides and especially antimonides prefer the NiAs structure also for the larger electron counts. 

Until very recently, the only example of a quasi-3-coordinate aluminum phosphide was (Me3SiCH2)2AlPPh2,76 which was reported to exist in solution as a monomer-dimer equilibrium. However, a crystal structure of... 

The thermal and photochemical reactions of Ir111 complexes (438) and (439), respectively, yield the same product species (440), R2 = Ph2, Me2, HPh.692 Kinetic studies indicate that the reaction involves the direct reductive transfer of the methyl to the phosphide via a three-centered transition state. The crystal structures of (438) and (439) (R2 = Ph2) are reported. 

Dimeric zinc complexes of tertiary phosphines, [Zn(PR3)I2]2, are also formed from zinc powder and R3PI2, (R = Me, Et, n-Pr, ra-Bu). The crystal structure of the ethyl derivative demonstrates the dimeric nature of the complexes.295 Metallation of diphenylphosphine with ZnEt2 results in a trimeric species with a Zn3P3 core and bridging diphenyl phosphide ligands. Two protic (HPPh2)... 

Phosphido-bridged multinuclear complexes have been formed from zinc chloride of the form [Zn4(PPh2)4Cl4(PRR 2)2], where R and R are alkyl or phenyl groups. Related tetrameric structures can be formed with a bridging dialkyl phosphide or (trimethyl)silylphenyl phosphide.303... 

In 1989 we reported on the synthesis and structure of the first l,3-diphospha-2-sila-allylic anion 3a [4], mentioning its value as a precursor for phosphino-silaphosphenes. In analogy to 3a we obtained the anions 3b-f [5] by treatment of 4 equivalents of the lithium phosphide 1 with the adequately substituted RSiC, of which 3b and 3c were investigated by X-ray analyses. The very short P-Si bond lengths (2.11-2.13 A) of 3a-c and the almost planar arrangement of Pl-Sil-P2-Lil indicate the cr-character of the Lithium P-Si-P allyl complex. 

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