Substitution coordinates

Endicott and Taube consider that there is cause for doubt over the generally-held views that Cr(bipy)3 is oxidised by an outer-sphere mechanism"". They suggest that, since the complex is very labile to substitution, coordination sites... 

During water-gas shift in pyridine solution, they isolated [PtH(py)L2]BF4, while from water-gas shift run in acetone solution, they isolated raft -[PtF[(CO)L2]BF4. The results indicated a solvent effect. That is, it was difficult to substitute coordinated pyridine with CO, but it was easier to substitute acetone with CO, via [PtH(Solvent)L2]OH + CO <-> [PtH(CO)L2]OH + Solvent. Following this important solvent-facilitated CO addition, they proposed a nucleophilic attack of OH-on the coordinated CO, via [PtH(CO)L2]OH <-> [PtH(COOH)L2]. The next step is thermal decomposition of the species, liberating C02, via the decomposition [PtH(COOH)L2] <-> [PtH2L2] + C02. CO addition was proposed to assist in decomposing the hydride to liberate H2. A more detailed description of the catalytic cycle is provided in Scheme 19. 

We are now close to being in a position to examine the effects on CO stretching parameter, for the isoelectronic isostructural series of first row carbonyl halides considered, of changes in metal, degree of substitution, coordination site, and halide. Along the sequence Cr(0), Mn(I), Fe(II), both 5 a and 2n populations fall. In other words, a higher oxidation state of the metal renders it at once a better a-acceptor and a poorer jr-donor perhaps a predictable result. Numerically the a -effect is the greater, but both are in the same direction, and parameters... 

The rather novel hydroxy MOP-derived Pd(ii) complex 63 [62], derived from the MOP chiral auxiliary 62, reveals an unexpected a-bond with the fully substituted coordinated carbon at 8 70.5, thus indicating that this carbon is no longer aromatic. 

In conclusion, subtle variations in the molybdothiol-complex catalysts—ligand substitution, coordination donor atom, and central metal ion—have large effects on the catalytic activity of acetylene reduction. The results presented here may offer useful information for a design of catalysts with optimal activity in such complex systems. 

The basic principles of the rm-method can be exemplified most clearly by the case of the diatomic molecule, a = 1,2, where, by Kraitchman s equation in the simple form for linear molecules, the equilibrium and the substitution coordinates with respect to the PAS of the parent, xea and x, respectively, are given by,... 

The left-hand side of Eq. 91 is computed from the substitution coordinates and is hence defined as the substitution inertial moment Fy of the parent. The first term of the right-hand side is the equilibrium moment F of the parent ... 

The moments 7 = l°g- g (harm) can be calculated from the ground state moments if the harmonic force field is known, although the present application is not very sensitive to uncertainty in the force-field [65]. The moments 7 are geometrically more consistent than the I°g (e.g., the inertial defect, Eq. 15c, expressed by the 7 practically vanishes for a planar molecule). For the present purpose, the substitution coordinates gsa, the substitution moments Ig, and the mass dependence moments Ig must be adequately redefined in accordance with the use of the moments lzg instead of I°g, but the important result, Eq. 99, remains unchanged. 

Olefin Substitution. Coordinated olefins are generally labUe hgands and their substitution is easily achieved by a more donating hgand. Ni(0) and Pt(0) biscarbene complexes (87) were prepared from the corresponding [(C0D)2M] complex by simple substitution (Scheme 15). When the reaction with IMes or SIMes was carried out in the presence of two equivalents of DMFU, the monocarbene diolefin complexes [(NHC)M(DMFU)2] (88) were obtained. ... 

The plane 90 determines, together with the equation of the receiving slit plane, the line of the intersection of these planes. In the coordinate system CSr the line of the intersection can be obtained easily from Equation (20) by setting the component z of the vector X to 0. Substituting coordinates of vector V and vector U in the coordinate system CS we obtain the equation of a straight line in the receiving slit plane ... 

In 1973, J. K. G. Watson [30] presented a new theory based upon isotopic mass effects to obtain a structure (known as r ) that was potentially a good approximation to r. Consider for simplicity a linear molecule, and compute the substitution coordinate zj of each of the N atoms using an appropriate SDS as previous described. Eq. (24) for the diatomic molecule applies for each of the N atoms of any linear molecule ... 

The errors of substitution coordinates can be derived ftom die errors of the principal moments of inertia or of the planar moments... 

The error 8(AP) has two different contributions. The first kind is associated with the experimental error of the planar moments it is usually negligible. The second kind, more severe and systematic, originates from model errors. TTie equations for the substitution coordinates are based on the assumption that the molecules are rigid. Since they are not, the eiqierimental ground state constants contain vibrational contributions that have a different mass-dependence. As a consequence, the substitution coordinates do not satisfy the basic relations (17-18). Another aspect of the same problem is the question of how close the coordinates are to the equilibrium coordinates rg. Costain [26] has shown that... 

U-A2 instead. It seems doubtful whether equation (31) really tells us anything about the errors of the rg coordinates. It can only be used to check the consistency of coordinates. Even if the substitution coordinates were completely consistent and fulfilled the basic assumptions (17-18) it would not automatically mean that they... 

The second common type of operationally defined structure is the so-called substitution or rt structure.10 The structural parameter is said to be an rs parameter whenever it has been obtained from Cartesian coordinates calculated from changes in moments of inertia that occur on isotopic substitution at the atoms involved by using Kraitchman s equations.9 In contrast to r0 structures, rs structures are very nearly isotopically consistent. Nonetheless, isotope effects can cause difficulties as discussed by Schwendeman. Watson12 has recently shown that to first-order in perturbation theory a moment of inertia calculated entirely from substitution coordinates is approximately the average of the effective and equilibrium moments of inertia. However, this relation does not extend to the structural parameters themselves, except for a diatomic molecule or a very few special cases of polyatomics. In fact, one drawback of rs structures is their lack of a well-defined relation to other types of structural parameters in spite of the well-defined way in which they are determined. It is occasionally stated in the literature that r, parameters approximate re parameters, but this cannot be true in general. For example, for a linear molecule Watson12 has shown that to first order ... 

Noting that 1/2 (/e + I0) /, where /, is calculated entirely from substitution coordinates, Watson12 has suggested using ... 

The principal application of the Kraitchman equations [Eq. (9)1 is for the determination of the atomic coordinates, at, bSi and cs. From a study of the rotational spectrum of the parent and of a species with single isotopic substitution the coordinates of the substituted atom may be determined. These coordinates are referred to as substitution coordinates or rs coordinates. Each new species yields new coordinates, and since all of the coordinates are in the same coordinate system, the calculation of substitution or rs bond distances and bond angles is a simple process. Costain,s demonstrated that there are definite advantages to the use of the Kraitchman equations to obtain molecular parameters. These advantages are sufficient to make the use of Kraitchman s equations the preferred method of structure determination from ground-state rotational constants. 

If one uses 0.006 u A2 as an estimate of the difference in pseudoinertia defect on substitution, the Costain rule16 for uncertainty in a substitution coordinate is obtained as follows ... 

Since the uncertainties in the other coordinates contribute to the uncertainty in av by either Eq. (15) or Eq. (16), a comparison of uncertainties is usually required to determine which is the best way to calculate a particular small coordinate. Of course, if isotopic data are not available, Eq. (15) or Eq. (16) may be used in lieu of Eq. (9) to compute a coordinate. Unfortunately, Eq. (15) and (16) are not satisfied exactly by substitution coordinates, and this must be taken into account. 

Rose Ml, Mascharak PK (2009) Photosensitization of Ruthenium nitrosyls to red light with an isoelectronic series of heavy-atom chromophores experimental and density functional theory studies on the effects of 0-, S- and Se-substituted coordinated dyes. Inorg Chem 48 6904-6917... 

Pyridine is a tertiary amine and a good base, as noted in Section 26.1.2. Because of this property, many of the electrophilic reagents used for aromatic substitution coordinate with the electron pair on nitrogen (an acid-base reaction). Specifically, the Lewis acids used in Chapter 21 for electrophilic aromatic substitution will coordinate with the electron pair on nitrogen, so they cannot be used. If electrophilic aromatic substitution does occur, the reaction is slow, and such reactions are difficult. Carbons 3 and 5, relative to nitrogen, have the greatest x-electron density (see IOC) and they are the major sites for reaction. The intermediates generated from pyridine in electrophilic... 

The complex exhibits the normal characteristic features of mono-arene Ru(II) complexes an alternation of the lengths of the C-C bonds for the coordinated arene and irregular Ru-C bond lengths, with the longest of 2.244 A (compared with 2.137 A for the shortest) being for the carbon attached to the phenyl substitutent. Coordinated arenes with extended ring systems can have a flexible structure, as illustrated for dihydroanthracene (DHA) complexes in Table 2.2 (vide infra). Such arene flexibility may play a role in interactions of Ru(II) arene complexes with DNA. 

If the isotopic substitution is consequently and consistently performed for each atom of the molecule, and the so-called substitution coordinates of each atom obtained, it is... 

Werner next turned to the geometry of the secondary valence (or coordination number). As shown in Table 2.2, six ammonias about a central metal atom or ion might assume one of several different common geometries, including hexagonal planar, trigonal prismatic, and octahedral. The table compares some information about the predicted and actual number of isomers for a variety of substituted coordination compounds. 

To evaluate the mass-dependence structure, various isotopic species are employed to calculate the substitution coordinates of each nonequivalent atom for a given parent. These substitution coordinates are then used to evaluate the moments of inertia, Eq. (5), which are called substitution moments of inertia 7 . The mass-dependence moment of inertia 7 is calculated from the relation... 

Here [7°]i (g = 1) is the ground-state moment of the parent isotopic species and [7 ]i is the substitution moment of inertia calculated from the set of substitution coordinates of the parent species. The dataset, the L isotopic species, is that needed for evaluation of a complete substitution structure. For a linear XYZ molecule, four isotopic species (including the parent) are needed for the substitution structure. From Eqs. (99) and (98), it follows for the parent, g = 1, that [7 ]i = 7 . The rationale for... 

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