Ligands weakest

Electronic effects on the reactions of [Rh(Por)h dimers and hydrides were probed by varying the porphyrin macrocycle. OEP and TPP vary considerably in their properties, with OEP being one of the strongest and TPP one of the weakest (7-donors among porphyrin derivatives. However. Rh(Por)]2, Rh(Por)H, and Rh(Por)r showed the same reactivity in a variety of reactions for both OEP and TPP, indicating that electronic effects relating to the porphyrin ligand have... 

Since the limit of detection for small molecule ligands, with modern ESI-Tof mass spectrometers, is approximately 0.05 pM, the concentration of the protein-ligand complex prior to the GPC spin column treatment must be about 0.25 pM. For initial protein and ligand concentrations >5 pM, this corresponds to values <20 pM, as indicated in Fig. 2.3. This is a desirable region for the GPC spin column studies, since one wants to be certain to detect ligands from the stronger as well as the weakest ligand binders. 

Table 6.1 The order of breakthrough for the example of Fig. 6.7 closely parallels the IC50 values from independent determinations using plate-based activity assays [10]. Kj values were measured for the strongest and weakest ligands in separate FAC-MS experiments.

Pt(a-alaninate)(H20)L] (L = NH3, py, Et2S, or DMSO) has shown that the acidity varies greatly with the nature of the cis-L. As expected, the 7r-donor NH3 causes the weakest acidic properties, whereas 7t-accepting ligands produce a marked increase in for the water. Similar studies on trans-[Pt(DMSO)-C1L(H20)] indicate that the acid strengths decrease in the order L = NH2OH > acetoxime > acetaldoxime. ... 

Fig. 2. Histogram of the formation constants of selected I 1 complexes. Formation constants generally increase with increasing metal hardness (increasing charge, decreasing ionic radius) and with increasing ligand hardness. Metal hardness increases from K+ to Zr4+ and ligand hardness from Cl " to OH". The most stable complexes are formed between hard metals and hard ligands, the weakest complexes are formed betweeen soft metals and soft ligands.

The distortion around six-coordinated Cr , the next cation in the periodic table, is so much larger than that around that the two weakest cation-ligand bonds have effectively disappeared, reducing the coordination number to 4. The coordination around Cr + is always tetrahedral, though one can sometimes observe two residual weak bonds in compounds such as CrOs (16031) which crystallizes with chains of corner-linked Cr04 tetrahedra packed in such a way that two very long octahedral bonds (lengths 322 and 334 pm) can still be identified (Fig. 8.10). 

In the case of mixed ligands photoreactivity may be predicted empiri- lly from considerations of the ligand field strencth (Adamson s rule), for O complex, the axis having the weakest average held as determined % the position of its respective ligands in the spectrochemical series will... 

Attempting to rationalize the strength of a metal-phosphorus bond in terms of the collective a, tt, and steric capacity of a coordinated phosphine is a difficult matter. Refer to the series you developed in Problem 11.13 and predict which ligands would form the strongest and the weakest M—P bonds. 

The X-ray structure of the L-Sr(Picrate)2 (L = p-tert-butyl-calix[4]arene-tetra(diethylamide)) is reported, as well as MD simulations on the L M2+ complexes in vacuo, in water, and in acetonitrile solutions for alkaline earth cations with a comparison of converging and diverging conformers.130 In the simulated and solid-state structures of the L M2+ complex, the ligand wraps around the complexed cations M2+ (more than it does with alkaline cations), which are completely encapsulated within the polar pseudo-cavity of L, without coordination to its counterion in the crystal or to solvent molecules in solution. In contrast to alkali cation complexes, which display conformational flexibility in solution, computations show that the alkaline earth cation complexes are of the converging type in water and in acetonitrile. Subtle structural changes from Mg2+ to Ba2+ are observed in the gas phase and in solution. Based on FBP calculations, a binding sequence of alkaline earth cations was determined Mg2+ displays the weakest affinity for L, while Ca2+ and Sr2+ are the most stable complexes, which is in agreement with the experiment. 

As described above, among the several closed-shell metal ions that form luminescent supramolecular entities with gold, thallium(I) forms the most numerous examples. While aurophilic attractions can be considered the upper extreme of the metallophilic interactions (with values up to 46 kJ mol-1), intermetallic contacts involving T1(I) centers appear as the weakest ones (even <20 kJ mol-1),46 which is explained by the enhancement of the Au---Au interactions and the weakening of the Van der Waals attractions between the s2 metal atoms produced by the relativistic effects.47 Nevertheless, the complexes in which this interaction appears are surprisingly stable, with additional electrostatic, packing forces, or the ligand architecture, responsible for this fact. 

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