Bite parameters

The reduction in the number of potential coordination sites from four to three on monosubstitution of squaric acid restricts the variety of possible coordination modes possible for these hgands. In the majority of the complexes prepared by HaU et al., the monosubstituted squarate ligands adopt a /u.-l,3 role, although in a few instances the ligands coordinate monodentately, adopting a pendant role 111, 123,132-137). Expectedly, as a consequence of bite-parameter considerations, chelation is observed only in the case of the large lead(II) ion (76). In... 

In the light of the structures of squarate-metal complexes reported so far it is clear that chelation by this ligand is limited to some alkaline- and rare-earth metal cations. This behaviour is explained by the large bite parameter of squarate dianion. 

X. Solans and co-workers, attempting to answer the question does squarate act in a bidentate manner , calculated the value of the bite parameter (b = d2/dj = d(0-0)/d(M-0), Figure 2) for the squarate ligand in a series of copper complexes of formula [Cu(C404)L], where L represents an A,A-biden-tate ligand. 

They estimated the bite parameter for a bidentate squarate ligand to be 1.70 A and dj to be 2.47 A (using the value of the bite parameter of the oxalate and the d2 bite for squarate). From this they concluded that the squarate should act as a... 

Texture profile analysis is an empirical technique of double-penetration that simulates two bites of the jaw action. Data obtained from the Force-time plots enable the evaluation of seven texture parameters (Figure 1). 

Hardness is an estimation of the required force to penetrate jelly (peak force during the first bite). The results showed that jellies prepared with non-amidated pectin had such a low hardness that values could not be measured in the used instrumental conditions. Therefore the non-amidated pectin will not be considered in the other parameters interpretation. This fact agrees with the general information that non-amidated pectins usually require more calcium ions than those already present in the juice for a good gelation (Pedersen, 1980 Pilgrim et al, 1991). 

In Table III is also given the distortion of the W(IV) complexes as demonstrated by the displacement from the plane as well as the change in bite angle of the equatorial cyano ligand with the M=0 moiety as well as the v(W = 0) as obtained from IR studies and the oxygen-17 NMR data. It is clear that a reasonable correlation between all these parameters, excluding the chemical shift for the [WO(CN)5]3 complex (Fig. 4a), exists. 

For monodentate ligands, e.g., triphenylphosphane, Tolman s cone-angle 0 and the electronic parameter x have a significant influence on the activity and the selectivity of the resulting catalyst system [24,25]. As regards bidentate ligands, which provide two coordination centers for the transition metal, the so-called bite angle fi determines the selectivity of the formed aldehydes. 

Note that these rates are not true rate constants as these overall rates will contain concentration and pre-equilibria parameters. Nevertheless, longer bridges, and thus wider bite angles lead to a relative increase in the rate of chain transfer. Ester formation for the wide bite angle ligands were assigned to the formation of trans complexes as mentioned above. 

Table 10 Natural bite angles, NMR chennical shifts, and Hammett parameter of Y in HRh(ligand)(CO)2 ...

The Ni—N bond distances, N-N bite distances, and N-M-N bite angles of Ni(II) macrocyclic complexes depend on the coordination number of the metal ion and the type of macrocycle. These structural parameters influence the electronic spectra and the electrochemical data. In general, Ni—N bond distances of square-planar complexes are shorter than those of the octahedral complexes because of the absence of electrons in dx2 . Furthermore, as the Ni—N bond distance in-... 

The bite angle makes the difference A practical ligand parameter for diphosphine ligands./. Chem. Soc., Dalton Trans., 1519-1529. 

This increase in and 0B is experimentally observed and is shown in Table 10, which is restricted to molecules with bidentate ligands that form four-membered chelate rings with small normalized bites. Exact agreement is not expected with Figure 32, which was calculated for i (unidentate/bi-dentate) = 1.0. Nevertheless, in all cases the largest distortion from the parameters of the regular octahedron is the increase in 0B, whereas A slightly increases. 

Detailed structural parameters are given in Table 13. On the other hand, the bidentate sulfur donor ligands in [Te (SPPh2)2N 2] form six-membered chelate rings with large normalized bites, b - 1.37, and the complex has an undistorted planar rectangular structure, 4>a = 47.0°, [Pg.60]

If the only way of obtaining the normalized bite of a bidentate ligand was from the crystal structure, the repulsion energy approach to stereochemistry would be limited. No matter how useful the theory may be in rationalizing the relation between different stereochemical parameters, it would have little predictive use since these other parameters are precisely determined at the... 

Extension to flexible seven-membered rings does not necessarily increase the normalized bite, as indicated by [Co(NH2CH2CH2CH2CH2NH2)3]Br3, for which the parameters are b = 1.40 and 6 = 27.9°.234 This is achieved by substantial buckling of the seven-membered ring. 

Table 3. Calculated 4A2 - 4T2 transition energies and inferred AOM parameter values for a Cr(A-A)3 complex with different Cartesian bite angles8...

Fig. 12. Definition of solid state structural parameters for tris chelate complexes with D3 symmetry 0 is the twist angle and is the projection of the bite angle a onto the plane which is perpendicular to the C3 symmetry axis, 0 is the pitch angle and is the angle subtended by the plane of the chelate ring and the C3 symmetry axis r, d, s and h are the metal ligand distance, bite distance, triangle edge, and the distance between the triangles, respectively. From Ref.82 ...

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