Tetrahedral environment

In this compound, synthesized in the low temperature reaction between diborane and excess ammonia, the cationic boron is coordinatively saturated in a tetrahedral environment. More recendy, cations having boron in tricoordinate or dicoordinate environments have been observed. These cationic species, called borenium and borinum ions, respectively, have been reviewed (19,20). 

The only sulfur isotope with a nuclear spin is which is quadrupolar (/ = 3/2) and of low natural abundance (0.76%). In view of these inherent difficulties and the low symmetry around the sulfur nuclei in most S-N compounds, S NMR spectroscopy has found very limited application in S-N chemistry. However, it is likely that reasonably narrow resonances could be obtained for sulfur in a tetrahedral environment, e.g. [S(N Bu)4], cf. [S04] . On the other hand both selenium and tellurium have isotopes with I = Vi with significant natural abundances ( Se, 7.6% and Te, 7.0%). Consequently, NMR studies using these nuclei can provide useful information for Se-N and Te-N systems. 

Binary mixtures that melt close to room temperature, namely AlCl3/N-butylpyri-dinium chloride mixtures, have also been investigated. Takahashi et al. [17] have also shown that for the 1 1 composition, [AlClJ predominates with a tetrahedral environment. At a ratio of 2 1, [Al2Cl7] becomes the main species. At high temperature (above 150 °C), some decomposition to [AlClJ and Al2Cl(3 was observed. 

C-Rh-Cl 150.7°) and some bending of the Rh—C-Obond (162.3°). Some short O—H and Cl-H intramolecular contacts may be responsible for the distortion though it has been suggested that in a distorted tetrahedral environment there may be an interaction between Rh dxz electrons and the CO 7r -orbital causing bending. 

Note the absence of the g subscripts here. Although the d orbitals are still centro-symmetric, the tetrahedral environment lacks a centre of inversion. The d orbitals are therefore not classified with respect to a symmetry element which doesn t exist the absence of the g subscript does not imply the opposite - i.e. u (ungerade or odd). 

In the next chapter we look at the intensities of d-d electronic transitions. We shall see that transitions between terms of the same spin-multiplicity are much more intense than those involving a change of spin. It is for this reason that our focus in the present chapter has been on the former. We have seen that for d d , d and configurations in octahedral or tetrahedral environments, there is only one so-called spin-allowed transition. For

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Blue copper proteins. A typical blue copper redox protein contains a single copper atom in a distorted tetrahedral environment. Copper performs the redox function of the protein by cycling between Cu and Cu. Usually the metal binds to two N atoms and two S atoms through a methionine, a cysteine, and two histidines. An example is plastocyanin, shown in Figure 20-29Z>. As their name implies, these molecules have a beautiful deep blue color that is attributed to photon-induced charge transfer from the sulfur atom of cysteine to the copper cation center. 

Iron-sulfur proteins. In an iroinsulfiir protein, the metal center is surrounded by a group of sulfur donor atoms in a tetrahedral environment. Box 14-2 describes the roles that iron-sulfur proteins play in nitrogenase, and Figure 20-30 shows the structures about the metal in three different types of iron-sulfur redox centers. One type (Figure 20-30a l contains a single iron atom bound to four cysteine ligands. The electron transfer reactions at these centers... 

Two copper(II) complexes of 2-acetylpyridine thiosemicarbazone, 8, were included in a study of complexes of 2-formylpyridine thiosemicarbazone [169]. [Cu(8-H)OAc] has a magnetic moment consistent with a monomeric copperfll) center and both it and [Cu(8)Cl2] have d,2-y2 ground state ESR spectra (Table 2). A d-d envelope and a magnetic moment of 1.68 B.M. have led others [178] to propose a distorted tetrahedral environment with metal-metal interaction for the brown complex, [Cu(8)Cl2]. 

The unsaturated silicon atoms form five bonds because of the donor. They have a tetrahedral environment and are four-coordinate. The adducts can be hydrolyzed very easily and are kinetically stable under normal conditions. One of the adducts, the THF adduct of Me2Si=N—Si(CMe3)3, has been isolated by Wiberg et al., as shown in Eq. (10).15... 

The novel tetrabasic ligand l,3-bis(5-methylpyrazole-3-carboxamido)propane forms a trinuc-lear Co111 Co11 Co111 complex (196). The tetradentate diamide-pyrazolyl chelates encircle the terminal trivalent metal ions while the central divalent Co is in a distorted tetrahedral environment provided by the four bridging pyrazolyl rings.881... 

The crystal structures of [Ag(l,4-dioxane)]AsF69 9 and [Ag2(l,4-oxathiane)](N03)295° have been reported. Two adducts of the 4-nitropyridine A-oxide with silver nitrate have been characterized, one is a mononuclear tetracoordinated compound [Ag(N03)(0NC5H4N02)2] and the other is a dinuclear pentacoordinated species [Ag2(N03)2(/u-0NC5H4N02)2(0NC5H4N02)2] (130).951,952 In the mixed compound /nmv-[RhCl2(py)4]N03-AgN03 exists the dinitroargentate(I) ion in a distorted tetrahedral environment 953... 

A number of zinc phosphine complexes have been synthesized due to interest in chemical vapor deposition for example, Zn(S-2,4,6-tBuC6H2)2(Ph2PMe) and [ZnI2(PEt3)]2.295 304 The structure of bis[(diphenylphosphino)propyl] zinc shows a highly distorted tetrahedral environment with an alkyl and a phosphorus donor binding from each bidentate ligand.318... 

Bharadwaj synthesized the zinc complex of a mixed donor cryptand (94). The X-ray structure shows that the zinc binds in the tetraamine cavity at the base of the ligand in a tetrahedral environment and not to the oxygen donors. This demonstrates the expansion potential of the cavity compared with the free ligand.740... 

The two chemically different zinc atoms show decidedly different coordination environments. Thus, the inorganic zinc atom (Znl) has an octahedral environment and is surrounded by four oxygen and two nitrogen atoms, while the organometallic zinc atom (Zn2) is in the pseudo-tetrahedral environment of one ethyl group and three oxygen atoms. 

Treatment of the known pentameric [MeZnSBu Js with pyridine and l,3,5-trimethylhexhydro-l,3,5-triazine produced dinuclear zinc adducts of the type [ MeZnSBu L, L = pyridine, l,3,5-trimethylhexhydro-l,3,5-triazine 162, whose solid-state structures were determined.227 The perspective view of 162, shown in Figure 75, emphasizes the highly puckered central four-membered (ZnS)2 ring and the tetrahedral environment of the zinc atoms. In the course of these studies, the solid-state structure of [MeZnSBu ls was also reinvestigated. 

The reaction of dabco (l,4-diazobicyclo[2.2.2]octane) with Me2Cd yields a 1 1 adduct 197, which adopts a linear polymeric structure (Figure 34).255 The cadmium atom is coordinated by two dabco units and two methyl carbon atoms giving rise to a distorted tetrahedral environment. Finally, the organocadmium adduct 198 (Figure 35) has been isolated from the reaction of Me2Cd with Cd[(SeP-/-Pr2)2N]2.256 The solid-state structure consists of dimeric units where each methylcadmium unit is coordinated to three selenium atoms. The geometry about the cadmium center is tetrahedral with a Cd-C distance of 2.16 A, which is comparable to that observed in other cadmium alkyl complexes. 

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