Tetrahedral distortion

A survey of crystal structures of 29 dialkyl peroxides (Table 11 and Sections II and V) provided a mean 0—0 bond length of 1.48 0.01 A and a O—O—C angle of 107 1.3° (with respect to the larger alkyl substituent) and 106 2.4° (for the smaller alkyl group). The torsion angle C—O—O—C shows a scatter between 180° and 125.8°. 

The largest number of reports on solid state geometries of dialkyl peroxides refers to compounds with either two tertiary substituents, molecules with one tertiary and 

2 5-fcrt-Butylperoxy-5-(oxiran-2-yl)-1 -(prop-2-ynyl)pyrrolidin-2-one (QAMTED) 1.479 154.2 145 

3 l-Methyl-9-(p-methoxyphenyl)bicyclo[4.3.0Jnona-6,8-dien-5-yl tert-butylperoxy 1.485 177.7 146 

4 ether (CIXFOF) Bis(heptachlorocyclopent-2-enyl) peroxide (44) (BEMSUH) 1.474 180.0 147 

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The cation has significant tetrahedral distortion from square planar geometry (P—Ir—P 150°) to minimize non-bonding interactions. It undergoes various oxidative addition reactions... 

The similar species Ir(PMe3)4 likewise shows tetrahedral distortion from square planar geometry (P-Ir—P 152.6-158.9°). It undergoes some remarkable oxidative addition reactions with species like H2O and H2S (Figure 2.72). 

We have argued that, once achieved, planar coordination in d systems is stable with respect to higher coordination number or tetrahedral distortion. The question arises then about what circumstances favour planarity in the first place. In particular, we enquire about the occurrence of tetrahedral verses square planar stereochemistry for d complexes. Why, for example, is the [Ni(CN)4] ion planar but [NiClJ tetrahedral ... 

An interesting example of a spin-admixed nonheme iron(lll) complex with S - (3/2, 5/2) ground state is the organometallic anion [Fe CeCls) which has four pentachloro phenyl ligands in tetrahedrally distorted planar symmetry [122]. 

Ni11 complexes of thiosemicarbazones derived from p-fluorobenzaldehyde and differently substituted thiosemicarbazides (434, 435) are square planar [NiL2] species with the S and hydrizine-N atoms in tram position to each other and a slight tetrahedral distortion in some cases.1235,1236... 

Distorted tetrahedral/distorted trigonal pyramidal (Cu-Cu 6.056A, 7.433A, and 7.671 A) 554... 

Ferrocene-containing sulfur ligands have been used in complex formation with zinc. 3-Ferro-cenyl-3-mercaptopropenale and l,l -bis(3-mercaptopropenale)ferrocene (112) form stable complexes as do their Schiff base derivatives with aniline or 1,2-ethylenediamine. The Fen/Fein redox couple shows only minor metal dependence, this is attributed to tetrahedral distortion.884... 

In the X-ray structures of both 3 and 4, the tetrahedral distortion is greater than that found in model A. Since there is an electronic preference for a square planar coordination, the pendant phenyl substituents in 3 and 4 likely result in further steric crowding and therefore in more distorted structures compared to model A. In the QM/MM model B an optimized 0 angle of 30° is found, close to the 34° angle of the X-ray structure. Since the phenyl and trimethyl phenyl groups are accounted for on a steric basis only in model B, the result supports the notion that the severely distorted coordination of the Pd center in 3 is due to a steric effect. 

The cycloheptyl rings adopt chair-like conformations characterized by the nearcoplanarity of atoms C(3), C(4), C(5) and C(6), which form the back of the chair, and atoms C(2), C(3), C(6) and C(7), which form the seat of the chair. Both nitro groups show small but only marginally significant tetrahedral distortions. 

In both cases the N2O2 coordination of the Ni(II) ion is essentially planar, though there is a slight tetrahedral distortion. However, the diamagnetism displayed by these complexes confirms that they are planar. 

Figure 120 shows the molecular structure of complex [CunL2]2 +, which has a planar CuN2S2 coordination with a slight tetrahedral distortion. 

As a result of the stepwise addition of electrons, the tetrahedral distortion of the central Ir-P4 fragment progressively increases, Table 1. 

The square-planar geometry (with slight tetrahedral distortion) of these derivatives can be proved by that of the related Rh(I) complex with 2,2/-bis [o-(diphenylphosphine)benzylidene]amine -6,6/-dimethyl-diphenyl, [Rh(PPNN)]+, Figure 23.26... 

As an example of thermodynamic treatment of electrochemical data, we can consider the case of the planar (with slight tetrahedral distortion) Cu(II) complex, [CuL]2+ shown in Scheme 4 (already mentioned in Chapter 5, Section 7).12... 

Muller et al. have shown that 24 oxygen atoms of the polyoxometalate [As4Mo6V7039]2- may be attributed to the structure of a rhombicuboctahedron. [44] Notably, a strong tetrahedral distortion of each ion is required to correspond each host to the polyhedron. This shell has been shown to complex a sulfate ion in the solid state. 

It has been reported that when Ceo is rapidly and nonhydrostatically compressed above 20 GPa at room temperature, it transforms into polycrystalline diamond [524]. Although Ceo can be considered as a folded graphite sheet, we must take into account that in the pentagons there is an important tetrahedral distortion making the transformation of Ceo into diamond likely easier than the HP-HT conversion from graphite, and it is possible to use this reaction for industrial production of diamonds. 

When copper is bound to one sulfur atom of a cysteine and two nitrogens of two histidines in an essentially tetrahedrally distorted - trigonal ligand environment (type I copper proteins), the excited levels are low in energy, and the values are reduced to about 5 x 10 ° s (29). Examples are blue copper proteins, like ceruloplasmin and azurin, and copper(II) substituted liver alcohol dehydrogenase (30-32). 

Macrocyclic N-donor ligands. Nickel complexes of macrocyclic ligands have been studied by cyclic voltammetry, and the irreversible or quasi-reversible couples Ni" L Ni L Ni L have been established. The structure of (124) has been reported and the co-ordination is essentially square-planar with a slight tetrahedral distortion. The reaction of [Ni(pn)3] with... 

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