Compounds of the Composition

Neither the cyclic nor the acyclic isomers of NgH have been observed experimentally only organic derivatives of cyclopentazadiene, c-NgH, are known, but their thermal stability is low. The acyclic isomers of NgH are supposed to consist of a double-bonded N2 unit with a hydrogen and an N3 substituent. Each of the (Z) and (E) isomers forms an s-cis or s-trans conformer depending on the spatial arrangement of the approximately linear N3 unit with respect to the N-N double bond. An ab initio SCF MO calculation at the STO-3G level showed that cyclopentazadiene is the most stable isomer of NgH, followed by the (E) s-trans isomer of acyclic NgH and the (Z) s-trans, the (E) s-cis, and the (Z) s-cis isomers. The decomposition to HN3 and N2 is exothermal for all isomers of NgH. A mutual conversion between the (Z) and (E) isomers is predicted not to occur [1]. 

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For compounds of the composition MX (M = cation, X = anion) the CsCl type has the largest Madelung constant. In this structure type a Cs+ ion is in contact with eight Cl-ions in a cubic arrangement (Fig. 7.1). The Cl- ions have no contact with one another. With cations smaller than Cs+ the Cl- ions come closer together and when the radius ratio has the value of rM/rx = 0.732, the Cl- ions are in contact with each other. When rM/rx < 0.732, the Cl- ions remain in contact, but there is no more contact between anions and cations. Now another structure type is favored its Madelung constant is indeed smaller, but it again allows contact of cations with anions. This is achieved by the smaller coordination number 6 of the ions that is fulfilled in the NaCl type (Fig. 7.1). When the radius ratio becomes even smaller, the zinc blende (sphalerite) or the wurtzite type should occur, in which the ions only have the coordination number 4 (Fig. 7.1 zinc blende and wurtzite are two modifications of ZnS). 

Compounds of the composition [Tc(9-aneN3)(CO)3]+ (29) and [Tc(HB(pyz)3) (CO)3] (30) have been described as being directly available from the reaction of 19 in toluene under CO, using exactly one equivalent of phosphine as a reductant. In the case of [HB(pyz)3], the long-known compound [TcOCl2(NNN)] may be the first intermediate that is subsequently reduced by the phosphine [33]. 

A series of technetium(I) J -diketonates have been prepared by refluxing 32 in the corresponding neat / -diketone. Due to the instability of the CO ligands trans to a ff-donor ligand, one of the COs can be substituted by an additional amine (L), forming compounds of the composition [Tc(OaO)(CO)3L] (61) [74,75],... 

Compounds of the composition [ReOCl3(N N)] have also been isolated with pyridine-2-aldi-mine and rr-acidic arylazopyridine and arylazoimidazole ligands." The products (101) are readily reduced by oxygen atom transfer reactions from Re to phosphorus atoms of phosphines which results in the formation of rhenium(III) complexes. Depending on the reaction condition and the phosphines used either mononuclear or binuclear compounds are formed." " Azo splitting reactions with arylazopyridines give access to arylimido and binuclear oxo/imido com-plexes. "" ... 

One of the complexes formed in the reaction of diphenylacetylene and iron dodecacarbonyl is a red, crystalline compound of the composition [Fe2(CO)6(PhC2Ph)], which, on reduction with sodium in liquid ammonia, gives dibenzyl (117). By analogy with the cobalt carbonyl complex, structure (XXXV M = Fe) is proposed, in which the 7r-elcctrons of the triple... 

The redox chemistries of di-, tri and tetra-nuclear Mo—S cyanide complexes have been discussed in relation to their electronic structures.135 Passage of oxygen into an aqueous solution of [Mo2S2(CN)s]6 leads to the formation of a dark violet mixed-crystal compound of the composition K4+J,[Mo2(S02)(S2)(CN)8] [Mo2(S02)(S2)(CN)8]1 -4H20 (x = 0.3). In the crystal the two anions, whilst structurally similar, are located at crystallographically independent positions each involves both molybdenum atoms surrounded by an approximately... 

Glucose is composed of 0 HiaOlS, 2HO, differing from starch, Hl4 01(, only by an addition of two equivalents of the elements of water, and two equi-valents of the water of Orystalltzation, with which, however, it parts when carefully exsiccated, leaving the compound of the composition CL Hls OlS. 

Evaporation of a solution of niobium oxysulphide in sulphuric acid and heating to 840° C. yields a compound of the composition Nb205.S03, which can be alternatively written Nb02.S04.Nb02, i.e. as hyponiobic sulphate. At 420° C. the product has the composition 2Nb205.S03.8... 

Under certain conditions HSiCl3 and tertiary amines form saltlike compounds of the composition R3NH+SiCl3. The chemistry of the SiClJ anion, which is isoelectronic with PC13, has been studied extensively 110 however, no structural data for SiCl3 have been reported. 

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