Weak ligand chemistry

Fig. 22. TPRS spectra for CO/HCOOH from Cu/Ni alloys of varying surface composition (100). (a) 37% Ni (b) 46% Ni (c) 54% Ni (d) 61% Ni (e) 68% Ni. The peak shifts indicate weak ligand effects (see text). Reprinted with permission from Journal of Inorganic Chemistry 17, 1978. Copyright 1978, American Chemical Society.

The equilibrium constants K and f)2 increase as the ligand pKt increases. The increases in porphyrin basicity and solvent polarity also increase / 2, indicating the importance of the charge neutralization factor in the iron(III) porphyrin coordination chemistry (Table 6).86 For preparative purposes, five-coordinate complexes of the weak ligands are conveniently used to avoid contamination of the mixed ligand species Fe(Por)XL. 

The size of the macrocycle coordination hole has a profound influence on its coordination chemistry thus in the weak ligand field of hydroporphyrinoid systems Ni2 + assumes the high spin state and binds extra axial ligands, while in the stronger ligand field of the corrin macrocycle the coordination sphere of the metal is saturated and diamagnetic complexes are generated [82]. 

Presumably, the polymer works because of a multiplicity of functional groups that behave as weak ligands in the proper conformation. Further experiments of this type with other functional groups that might behave as ligands for inorganic salts should be tried. Perhaps, combinatorial chemistry can be applied here. 

SOLID SOLVATES THE USE OF WEAK LIGANDS IN COORDINATION CHEMISTRY... 

Solid Solvates The Use of Weak Ligands in Coordination Chemistry 113... 

Another interesting example of flexibility of the framework [55] has been found" in the polymer constructed from Cu(II) and the ligand, 5-sulfoisophthalate. The unique properties of this material can be attributed to the coordination flexibility of the structure, imparted by the use of a linker with the potential for both strong and weak ligand interactions. The two carboxylate donors on the ligand bind relatively strongly to Cu(II) that help maintain the overall structure while chemistry can take place at the weaker sulfonate-metal bonds reversively. The low-temperature structure of the polymer consists of a tetramer of Cu(II) ions as the SBU linked by two... 

It is extremely challenging to define solution speciation based on Eu(III) luminescence data in solutions that only contain weak ligands such as buffer, or counter ions such as nitrate, chloride, or triflate. This is in large part due to the complexity of the solution chemistry of... 

Despite the weak basicity of isoxazoles, complexes of the parent methyl and phenyl derivatives with numerous metal ions such as copper, zinc, cobalt, etc. have been described (79AHC(25) 147). Many transition metal cations form complexes with Imidazoles the coordination number is four to six (70AHC(12)103). The chemistry of pyrazole complexes has been especially well studied and coordination compounds are known with thlazoles and 1,2,4-triazoles. Tetrazole anions also form good ligands for heavy metals (77AHC(21)323). 

The group at Johnson and Johnson has published several reports on their efforts to find potent H3 antagonists. High-throughput screening using the recombinant human receptor identified the imidazopyridine RWJ-20085 (30) as a weak H3 receptor ligand K — 4 pM). Medicinal chemistry efforts then led to the discovery of the piperidine propyloxy compound (31) [100]. This imidazopyridine has a A) at the human H3 receptor of 2nM and... 

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