Distorted octahedral structures

The most important members of this class are the osmium nitrido, and the osmyl complexes. The reddish-purple K2[OsNCl5] mentioned above is the result of reducing the osmiamate. The anion has a distorted octahedral structure with a formal triple bond Os=N (161pm) and a pronounced /ram-influence (pp. 1163-4), i.e. the Os-Cl distance trans to Os-N is much longer than the Os-Cl distances cis to Os-N (261 and 236 pm respectively). The anion [OsNCls] also shows a rram-effect in that the Cl opposite the N is more labile than the others, leading, for instance, to the formation of [Os NCl4] , which has a square-pyramidal structure with the N occupying the apical position. 

Complexes of the divalent metals [M(ttcn)2]2+ undergo electrochemical oxidation to paramagnetic [M(ttcn)2]3+. Red [Pd(ttcn)2]3+ has a tetragonally distorted octahedral structure (d7, Jahn-Teller distortion) with Pd—S 2.356-2.369 A (equatorial) and 2.545 A (axial) in keeping with the ESR spectrum (gj = 2.049, gy = 2.009) which also displays 105Pd hfs. Similarly, electrochemical oxidation of the palladium(II) tacn complex (at a rather lower... 

Au(diphos)2 and Au(diars)2 can be oxidized to gold(III) species [127]. These tend to add halide ions so that Au(diars)2lJ has a distorted octahedral structure with very weakly bound iodides (section 4.12.5). 

Both Fe(II) amidinates depicted in Scheme 137 react readily with CO to give the new diamagnetic Fe(II) dicarbonyls [But(NR)2l2Fe(CO)2 (Scheme 138). The compound with R = Pr was structurally characterized, which showed it to have a strongly distorted octahedral structure with the carbonyls in a cis arrangement. ... 

Although the bulk of work with NOz as a ligand features Co111, nitrite can also be O- or N-bonded to Co11, and both modes have been observed in complexes formed by the reaction of several PR3 compounds with Co(N03)2, as well as in mixed nitro/nitroso complexes.375 The product Co(NO)(N02)(PEt3)2 reacts with dioxygen to form Co(N03)2 (OPEt3)2, a distorted octahedral structure with bidentate nitrate and cis phosphine oxides (102). 

Information about the possible structures of molybdate and its pro-tonated forms in solution has been obtained from molecular orbital calculations (62). By considering bond orders obtained from a Mulli-ken population analysis and the agreement between experimental and theoretical UV spectra it was concluded that [Mo04]2 and [HMoOt I are tetrahedral and that the neutral acid is octahedral. For the latter a somewhat distorted octahedral structure based on the formula Mo02(OH)2(H20)2 was proposed (62). The alternative structure Mo03(H20)3 was not taken into account in the calculations. 

Due to this mixing a Jahn-Teller molecule is expected to be rather fluxional and this often makes it difficult to detect the effect. It is usually observed in crystals where due to the so-called Jahn-Teller cooperativity a static distortion may occur in the crystal. The most typical examples are the tetragonally distorted octahedral structures, such as MnFs or KCuFs. 

Os (Tp)(NHPh)(Cl)2] exhibits low acidity and low basicity it is less acidic and less basic than aniline. It was suggested that this is a result of both Os— N(amide) tt bonding and the inductive effect of the oxidizing Os(IV) center. Reaction of [Os (Tp)(NHPh)(Cl)2] with MeOTf at 80 °C for 6T produces [Os (Tp)(NHPh)(OTf)2] and CH3CI. The X-ray structure of [Os (Tp)(NH-Ph)(OTf)2] shows a distorted octahedral structure Os— N(amido) = 1.939A and... 

The first osmium(IV) thiolato complex, [Os(salen)(SPh)2] (132), was prepared by the reduction of [0s(0)2(salen)] with thiophenol in CH2Cl2. The complex has a distorted octahedral structure, and both phenyl groups tilt away from the methylene bridge of the salen ligand, which is in the gauche confirmation. The mean Os—S distance is 2.32 A, which is shorter than that (2.415 A) in [Os2(Et2dtc)6](PF6)2 (Et2dtc = A,A-diethyldithiocarbamate). 

Fig. 15. The oloso distorted octahedral structure of the cobalt carbonyl acetylene complex Co4(CO)ioC2Et2 (50).

The naturally occurring dioxide exists in three crystal forms anatase, rutile and brookite. While rutile, the most common form, has an octahedral structure. Anatase and brookite have very distorted octahedra of oxygen atoms surrounding each titanium atom. In such distorted octahedral structures, two oxygen atoms are relatively closer to titanium than the other four oxygen atoms. Anatase is more stable than the rutile form by about 8 to 12 kJ/mol (Cotton, F.A., Wilkinson, G., Murillo, C.A and M Bochmann. 1999. Advanced Inorganic Chemistry, 6 ed, p. 697, New York John Wiley Sons) Other physical properties are density 4.23g/cm3 Mohs hardness 5.8 g/cm ( anatase and brookite) and 6.2 g/cm ( rutile) index of refraction 2.488 (anatase), 2.583 (brookite) and 2.609 (rutile) melts at 1,843°C insoluble in water and dilute acids soluble in concentrated acids. 

Anhydrous RuO has a tetragonal rutile structure with a slightly distorted octahedral structure, there being two sets of Ru-0 distances at 1.917(8) and 1.999(8) A [645] and has an extensive chemistry as a heterogeneous oxidation catalyst, a topic beyond the scope of this book. It is rarely used as a precursor for Ru oxidations, the hydrated form RuO. nH O (for brevity written below simply as RuO ) being much more effective in this respect. A procedure for converting inactive RuO (presumably the anhydrous form) to the hydrated RuO used in catalytic oxidations has been described [243]. 

The anhydrous form is rarely if ever used for catalysis, as is the case with anhydrous RuOj. It exists in two modifications. The black a-form is made by heating P-RuClj to 600°C in vacuo, and has the laminar a-TiClj structure also found in CrClj and FeClj with a distorted octahedral structure (Ru-Cl distance 2.40 A). The brown P-form has the P-TiClj structure with linear polymers of RuClj units, the metal atoms having distorted octahedral coordination (Ru-Ru 2.68 A, Ru-Cl 2.30(7) and 2.39(7) A). Infrared spectra and magnetic susceptibility data were recorded for both forms [712]. The toxicological properties of RuClj have been listed it may give off toxic RuO when heated, and is mildly toxic by intraperito-neal routes [238]. 

The 12-membered tetraaza-macrocyclic ligand with four pendant pyrazole groups, L6, was synthesized by the reaction of l-(hydroxy-methyDpyrazole with 1,4,7,10-tetraazacyclododecane in MeCN. The Ni(II) complex [NiLe]I2 formed a distorted octahedral structure with... 

Figure 5. The distorted octahedral structure of mex-H2jr(PPh2,h (32)...

The cocondensation of chromium vapour and the phosphorus ligand is used to prepare [Cr(dmpe)3] and the trimethyl phosphite complex [Cr P(OMe)3 6] (Table 8). The former has a distorted octahedral structure, and the latter forms a seven-coordinate hydride CrH2 P(OMe)3 5 which, with other chromium(II) complexes of P donor ligands, is considered in Section 35.3.4. 

The vast majority of MoO + core complexes are six-coordinate and mostly of distorted octahedral structure. Some non-octahedral complexes are known. In the octahedral structure the two Mo—O, bonds are invariably cis to each other. The strong o- and jr-donor nature of the oxo ligands makes it favorable for them to avoid competing for the same p and d orbitals. If the oxo groups were tram they would be forced to share two d orbitals and one p orbital. By residing on adjacent coordination sites they are forced to share only a single d orbital. 

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