Quinquedentate macrocycle

As regards other coordination compounds of silver, electrochemical synthesis of metallic (e.g. Ag and Cu) complexes of bidentate thiolates containing nitrogen as an additional donor atom has been described by Garcia-Vasquez etal. [390]. Also Marquez and Anacona [391] have prepared and electrochemically studied sil-ver(I) complex of heptaaza quinquedentate macrocyclic ligand. It has been shown that the reversible one-electron oxidation wave at -1-0.75 V (versus Ag AgBF4) corresponds to the formation of a ligand-radical cation. Other applications of coordination silver compounds in electrochemistry include, for example, a reference electrode for aprotic media based on Ag(I) complex with cryptand 222, proposed by Lewandowski etal. [392]. Potential of this electrode was less sensitive to the impurities and the solvent than the conventional Ag/Ag+ electrode. 

Dockal etal. [57] used slow-scan CV to determine the 21 values for 17 Cu(II/I) complexes in 80% methanol —20% water (w/w) - including nine complexes with macrocyclic terdentate, quadridentate, quinquedentate, and sexaden-tate thioethers and eight complexes with acyclic quadridentate ligands containing thioether sulfur and/or amine nitrogen donor atoms. (In naming the denticity of multidentate ligands, Dwyer, Lions, and coworkers have pointed out that dentate is a Latin root and proper nomenclature requires that Latin prefixes be used. 

Simple macrocyclic quadridentate complexes can be synthesized by template reactions from ethers derived from salicylaldehyde and diamines in the presence of appropriate metal ions such as nickel(II) (equation 3).35>36 However, these reactions can also be carried out quite effectively in the absence of metal ions to yield the free ligands, which can be obtained by hydrolysis of the complexes. An iron(II) macrocyclic quinquedentate chelate of this type has been produced by template synthesis (equation 4).37... 

Bis(l,2-diaminoethane)copper(II) perchlorate undergoes reaction with acetone to give the quinquedentate complex (43), which is converted to the macrocyclic complex (44) on addition of base, usually excess 1,2-diaminoethane (Scheme 8).86 Similar cobalt(I3) complexes cannot be prepared by metal template methods. 

A full report on the structural determinations of the complexes [Zn(H2L)(H20)2]-CI2 and Zh2L2 [H2L = 2,6-diacetylpyridinebis-(2 -pyridylhydrazone)] mentioned in last year s report has appeared. Reaction of Zn(S03CF3)2 with the macrocycle (6 H2L) in the presence of a tertiary amine such as triethyl- or tri-n-propylamine, yields the complexes [ZnL(amine)] n.m.r. studies indicate the co-ordination geometry to be square-pyramidal with the amine in the apical position. The complex [ZnL],H20 of the quinquedentate Schiff base (7 H2L) has been prepared the zinc environment is a distorted trigonal bipyramid (Zn—O = 1.95 A Zn—N = 2.11 — 2.16A). ... 

The Schiff base condensation of 2,6-diacetylpyridine with 4,7-dithiadecane-1,10-diamine yields the similar NjSj macrocycle (129). This ligand is able to form complexes with iron(II) but its mode of coordination adapts to the monodentate coligand. Thus X-ray crystal structures show that in [Fe(L)(NCS)] and [Fe(L)(MeOH)Cl]+ (L = 129) the iron atom has a distorted octahedral geometry. In the first complex the macrocycle is quinquedentate and wraps around the iron atom. In the second complex the macrocycle is quadridentate with one sulfur atom weakly coordinated and one free. A compound with the formulation [Fe(L)(NCS)2] (L = 129) has been observed and evidently exists in three different forms (from IR, Mossbauer and magnetic data). Although X-ray structural data are not available on these isomers it is likely that they also reflect different ligand conformations of the NjS, macrocycle. 

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