Tetraazamacrocyclic ligand

CONTENTS Preface. George W. Gokel. Cryptophanes Receptors for Tetrahedral Molecules, Andre Collett, Jean-Pierre Dutasta and Benedict Lozach. Inclusion Polymerization in Steroidal Canal Complexes, Kiichi Takemoto, Mikiji Miyata. Functionalized Tetraazamacrocycles Ligands with Many Aspects, Thomas A. Kaden. Calixarenes as the Third Supramolecular Host, Seiji Shinkai, Kyushu University, Japan. Fluorescent Chemosensors for Metal and Non-Metal Ions in Aqueous Solutions Based on the Chief Paradigm, Anthony W. Czamik. Index. 

A new optically active tetraazamacrocycle ligand, 27 ,37 -cyclohexano-1,4,7,10-tetra-azacyclododecane was covalently anchored on micelle-templated silicate (MTS) surface. The... 

Figure 10-2. Although they are relatively rare in biology, organometallic compounds with metal-carbon bonds are important. An typical example is coenzyme B12. The cobalt is co-ordinated to a tetraazamacrocyclic ligand, and has one axial nitrogen donor heterocyclic ligand and one axial alkyl group. The figure illustrates only the core of the macrocycle and the axial groups.

Figure 9. Visualization of the lone pair directionality (complementarity) of three tetraazamacrocyclic ligands L5, L6 and L7.19...

SATURATED, UNSUBSTITUTED TETRAAZAMACROCYCLIC LIGANDS AND THEIR COB ALT(IH) COMPLEXES... 

However, using a tetraazamacrocyclic ligand (L), this has been achieved in both H20 and CN solutions, and a paramagnetic complex AgL2+ has been isolated. Normally, however, Ag11 species can be obtained only by oxidation. 

Cobalt complexes with 14-membered tetraazamacrocyclic ligands have been investigated and successfully employed as catalysts for electrochemical and photochemical reduction of C02 and H20.230 One such complex low-spin [Co(I)HMD] + (HMD = 5,7,7,12,14,14,-hexamethyl-l,4,8,ll-tetraazacyclotetradeca-4,ll-diene (hex-amethylcyclam)) reacts with C02 in H20 and in CH3CN to form the N-rac-[CoHMD(C02)]+ species which is sufficiently stable in dry CH3CN and in a C02... 

The Ni(I) forms of these hydroporphyrin model compounds have not been isolated, and thus have been studied in solution by EXAFS (see below). However, several Ni(I) complexes with tetraazamacrocyclic ligands have been isolated and structurally characterized by X-ray crystallography [66 - 70]. These studies showed that depending on the macrocyclic ligand s flexibility, reduction of Ni(II) to Ni(I) was associated with either expansion of the Ni-N distances, a distortion in the NiN4 core (i. e., two sets of significantly different Ni(I)-N bond lengths) or both expansion and distortion. 

PCTA is a tetraazamacrocyclic ligand bearing a pyridine chromophore and three carboxylic functions. It offers seven potential donor atoms able to coordinate a lanthanide. The stability constant of 20.3 for (Eu )PCTA is acceptable in order to work in the presence of competing ions or ligands [101]. A well known complex 37 is based on a phosphonate equivalent of DOTA Tb(III)-3,6,9-tris(methylene phosphonic acid -butyl ester)-3,6,9,15-tetraazabicyclo[9.3.1]-pentadeca-l (15),ll,13-triene (Tb-PCTMB) [102,103] k azx. = 270nm, 8259 = 3,000cm X (H2O) = 4.98 ms [104] tot (H2O) = 0.51. As one could expect from a single pyridine chromophore the absorption is rather low and the absorption falls below the workable window (300-340 nm) Amax = 269 nm, 6259 = 4,600 cm ... 

Tetraazamacrocyclic ligands incorporating an intracyclic terpyridine chromophore 39 was described [106, 107], as expected the absorption maxima (335 nm) was more advantageous compared to 38. The physical characteristics were described X (H2O) = 1.06 ms, luminescence decays indicated that no water molecule is coordinated to the metal ion suggesting that the nine binding sites provided by the ligand are coordinating the lanthanide. No decomposition of these complexes was observed after 1 day in... 

There are many examples of the stabilization of unstable 3+ oxidation states by complex formation with macrocyclic ligands. and Cu are stabilized by complex formation with tetraazamacrocyclic ligands. The most universal ligand for the stabilization of unstable oxidation states is [9]aneS3 (L), which forms coordination compounds of general type ML with many unstable ions, e.g., Ag Pd % and Pt. ... 

There is a brief discussion of kinetics of complex formation of nickel(III) complexes of tetraazamacrocyclic ligands such as cyclam with chloride, bromide, thiocyanate, and sulfate in a review of the synthesis and reactions of nickel(III) complexes.Such reactions are really rather fast—it is at nickel(IV) that slow substitution may be expected, if not obscured by rapid oxidation of ligands. 

A radical mechanism was found for the formation of alkyl-chromium(III) complex [Cr(L)R] from the reactions of [CrCL)] " with alkyl halides, RX (L = tetraazamacrocyclic ligand [15]aneN4). ... 

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