Complex pyramidal

Oltvai, Z.N. and Barabasi, A.L. (2002) Systems biology. Life s complexity pyramid. Science 298, 763. ... 

Simple nickel salts form ammine and other coordination complexes (see Coordination compounds). The octahedral configuration, in which nickel has a coordination number (CN) of 6, is the most common stmctural form. The square-planar and tetrahedral configurations (11), iu which nickel has a coordination number of 4, are less common. Generally, the latter group tends to be reddish brown. The 5-coordinate square pyramid configuration is also quite common. These materials tend to be darker in color and mostiy green (12). 

Phosphoms oxychloride has strong donor properties toward metal ions. The remarkably stable POCl —AlCl complex has been utilized to remove AlCl from Friedel-Crafts reaction products. Any POX molecule contains a pyramidal PX group the oxygen atom occupies the fourth position to complete the distorted tetrahedron (37). Some properties of phosphoms oxyhaUdes ate presented in Table 8. 

The a-rhombohedral form of boron has the simplest crystal stmcture with slightly deformed cubic close packing. At 1200°C a-rhombohedral boron degrades, and at 1500°C converts to P-rhombohedral boron, which is the most thermodynamically stable form. The unit cell has 104 boron atoms, a central B 2 icosahedron, and 12 pentagonal pyramids of boron atom directed outward. Twenty additional boron atoms complete a complex coordination (2). 

Syntheses, crystallization, structural identification, and chemical characterization of high nuclearity clusters can be exceedingly difficult. Usually, several different clusters are formed in any given synthetic procedure, and each compound must be extracted and identified. The problem may be compounded by the instabiUty of a particular molecule. In 1962 the stmcture of the first high nuclearity carbide complex formulated as Fe (CO) C [11087-47-1] was characterized (40,41) see stmcture (12). This complex was originally prepared in an extremely low yield of 0.5%. This molecule was the first carbide complex isolated and became the foremnner of a whole family of carbide complexes of square pyramidal stmcture and a total of 74-valence electrons (see also Carbides, survey). 

A number of transition-metal complexes of RNSO ligands have been structurally characterized. Three bonding modes, r(A,5), o-(5)-trigonal and o (5 )-pyramidal, have been observed (Scheme 9.1). Side-on (N,S) coordination is favoured by electron-rich (et or j °) metal centers, while the ff(S)-trigonal mode is preferred for less electron-rich metal centres (or those with competitive strong r-acid co-ligands). As expected ti (N,S)... 

The hydrolytic sensitivity of thionylimines is also displayed by L M-RNSO complexes, which produce the corresponding LnM-S02 complexes. The ease of hydrolysis of these metal complexes follows the order o-(5)-pyramidal > o-(5)-trigonal > 7c(N,S). ... 

Table 4.3 indicates that octahedral coordination is a common mode for Li. Less usual is planar 6-fold coordination (Fig. 4.8a), pentagonal pyramidal coordination (Fig. 4.8i) or irregular 6-fold coordination (Fig. 4.9a). Examples of 7-fold coordination are in Fig. 4.9b and c. Lithium has cubic 8-fold coordination in the metallic form and in several of its alloys with metals of large radius. It is also 8-coordinate in the dilithionaphthalene complex shown in Fig. 4.9d here the aromatic... 

Figure 4.11 Molecular structures of typical crown-ether complexes with alkali metal cations (a) sodium-water-benzo-I5-crown-5 showing pentagonal-pyramidal coordination of Na by 6 oxygen atoms (b) 18-crown-6-potassium-ethyl acetoacetate enolate showing unsymmelrical coordination of K by 8 oxygen atoms and (c) the RbNCS ion pair coordinated by dibenzo-I8-crown-6 to give seven-fold coordination about Rb.

Tin(II) chlorides are similarly complex (Fig. 10.5). In the gas phase, SnCh forms bent molecules, but the crystalline material (mp 246°, bp 623°) has a layer structure with chains of comer-shared trigonal pyramidal SnClsl groups. The dihydrate also has a 3-coordinated structure with only I of the H2O molecules directly bonded to the Sn (Fig. I0.5c) the neutral aquo complexes are arranged in double layers with the second H2O molecules interleaved between them to form a two-dimensional H-bonded network... 

SnO and hydrous tin(II) oxide are amphoteric, dissolving readily in aqueous acids to give Sn" or its complexes, and in alkalis to give the pyramidal Sn(OH)3 at intermediate values of pH, condensed basic oxide-hydroxide species form, e.g. [(OH)2SnOSn(OH)2] and [Sn3(OH)4] +, etc. Analytically, the hydrous oxide frequently has a composition close to 3Sn0.H20 and an X-ray study shows it to... 

All 4 trihalides are volatile reactive compounds which feature pyramidal molecules. The fluoride is best made by the action of CaF2, Znp2 or Asp3 on PCI3, but the others are formed by direct halogenation of the element. PF3 is colourless, odourless and does not fume in air, but is very hazardous due to the formation of a complex with blood haemoglobin (cf. 

The solubility of AS2O3 in water, and the species present in solution, depend markedly on pH. In pure water at 25°C the solubility is 2.16 g per lOOg this diminishes in dilute HCl to a minimum of 1.56g per lOOg at about 3 m HCl and then increases, presumably due to the formation of chloro-complexes. In neutral or acid solutions the main species is probably pyramidal As(OH)3, arsenious acid , though this compound has never been isolated either from solution or otherwise (cf. carbonic acid, p. 310). The solubility is much greater in basic solutions and spectroscopic evidence points to... 

---