Macrocyclic Quadridentate Ligand

Sadasivan et al. studied cobalt III) complexes containing 5,7,7,12,14,14-hexa-methyl-l,4,8,ll-tetraazacyclotetradeca-4,ll-dien. A, the Cu(II) and Ni(II) complexes of which had been extensively investigated by Curtis and co-workers 

The other complexes such as dicyano, diazido, dinitro, dibromo and diisothio-cyanato complexes are prepared analogously. The diaqua complex, [ oA(H20)2]-( 104)3, is synthesized from the free amine prepared by urtis method. Equimolar ethanolic solutions of the free amine and 0(0104)2 6 H2O are mixed and after filtering out the precipitate, the mixed solution is boiled in the presence of har-coal Activated Norit. While boiling, air or oxygen is passed through. After some 

The IR spectra, chemical properties and visible spectra showed that the unidentate ligands are trans to each other, indicating square planar coordination of the Schiff base macrocycle. 

The above Co(II) derivative has a noncoordinating anion (BF4 ) and is quite stable in nitromethane toward oxidation until coordinating anions are introduced into the system. Thus, when lithium chloride is added to a nitromethane solution of [Co(TTP)] (BF4 2 and exposed to air, the resulting solution gives cw-[CoCl2(TTP)]-BF4 after adding ether. The bromide derivative, cw-[CoBr2(TTP)] BF4, is prepared in a similar manner. 

The same dichloro complex is prepared by air-oxidation of the components in a one-step procedure either cobalt(II) perchlorate hexahydrate and excess lithimn chloride or anhydrous cobalt(II) chloride and excess lithium perchlorate are stirred 

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Bernardo etal. [51] subsequently determined the potentials of a series of copper(II/I) complexes formed with 14-membered macrocyclic quadridentate ligands involving amine nitrogen and thioether sulfur donor atoms and found that the substitution of each sulfur donor atom by an amine nitrogen resulted in an average decrease of 0.3 V in the Cu(II/I) potential. Since the Afcu L values had been determined previously for these systems [99], Bernardo et al. were able to calculate the A (jji values using Eq. (9). The latter values proved to be nearly constant, indicating that Cu(I) does not discriminate... 

The absorption and c.d. spectra of 4,4 -(i -propylene-di-iminato)di(3-penten-2-one)-copper(ii) (133) has been interpreted to show that the complex is tetrahedrally distorted with the absolute configuration A 2f-ray diffraction has confirmed this. The synthesis of new binucleating agents (134) and their dimeric cupric complexes has been reported. The new macrocyclic quadridentate ligands of type (135) form... 

Two studies have appeared for the base hydrolysis of complex ions of the type ra j-[Co(L)XY] + containing a macrocyclic quadridentate ligand [L = (19) or (20)] and two unidentate ligands (X and Y). When X = NOg and Y = Cl, loss of chloride ion proceeds at much the same rate for L = (19) and (20), the extra methyl groups in (20) having little or no effect upon the base-hydrolysis rates. Complex ions in which X = Y = NH3 have also been prepared and rate data are reported for the base hydrolysis of the first ammonia molecule in 2,6-lutidinium buffers [L = (20), pH 6.0—6.8] or in carbonate buffers [L = (19), pH 9.8—10.6]. This time, the second-order rate constant at 298.2 K increases markedly from 3.2 dm mol s [L = (19)] to 7.6x 10 dm mol s- [L = (20)] as the number of peripheral methyl groups is increased. 

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... 

As far as quadridentate ligands are concerned, the easiest attainment of the Ni state, denoted by the less positive redox potential, is observed with the 14-membered macrocycle, 5, known as cyclam. Both contraction and expansion of tetramine ring atomicity, to 12 and to 16, respectively, makes the potential more positive, thus destabilizing Ni with respect to Ni Moreover, the isomeric 14-membered macrocycle, 6 (isocyclam) stabilizes the Ni state to a much lesser extent than cyclam. Notice that the two macrocyclic complexes simply differ in the sequence of the five-... 

Cyclam, tet a, tet b, and trans[14]diene are a group of macrocyclic quadridentate nitrogen donor ligands. 

The formation and dissociation kinetics for the complexation of Cu, Zn, Co and Ni with the quadridentate l,4,8,ll-tetramethyl-l,4,8,ll-tetraazacyclotetradecane to give five-coordinate species have been reported.1203 The rate order (Cu > Zn > Co > Ni) is the same as that for H2O exchange, but the rates are much slower, probably owing to conformational changes occurring in the ligand. The dissociation is acid-catalyzed the five-coordinate species are found to be much less kinetically inert than four- or six-coordinate complexes. No macrocyclic effect was observed. 

Square-planar complexes of quadridentate macrocyclic ligands 204... 

Schrauzer (52) also found that a macrocyclic sulfur quadridentate (XXIV) could be formed by the sequence of Scheme I if the iodomethane is replaced by a,a -dibromo-o-xylene. This type of ligand is of interest... 

Macrocyclic Ligands. The structure of LCu2Cl2,6H20 [LH2 = quadridentate Schiff base macrocycle (111) formed by condensation of propane-l,3 diamine and 2-hydroxy-5-methylisophthalaldehyde] has been determined. The cyclic structure consists of two copper atoms held in a dinuclear arrangement (112) by the planar N4O2 donor set ... 

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