Complexes with Multidentate Ligands

In the ca of [Co(ida)(dien)] , three isomers, tran O), s-cis(0) and u-ciMP), were separated in that order of elution the isomeric composition is given in Fig. 3.2. With [Co(mida)(dien)], two isomers, trans and s-cis, were obtained, but the u-cis isomer was not found. The ligand pdc should only span meridional edges of an octahedron and only the trans isomer was foimd of [Co(pdc)(dien)]. In accordance with a general trend on trans and cis isomeric complexes, the trans isomers were first eluted. 

The same workers prepared [Co D-asp)(dien)] (D-asp = D-aspartate) by the reaction of [CoClsfdien)] and Ag2D-asp at activated charcoal. The resulting solution was chromatographed on a cation exchanger column (Dowex 50W-X8, Na form) by ehition with 0.3 mol/dm NaC104. The possible three isomers were isolated with different yields (Fig. 3.3). 

The sexadentate ligand, (L)-ethylenediamine-iV,Ar-diacetic-iV -n[ionosuccinic acid (Htcddams), can form two geometric isomers with cobalt(III) (Fig. 3.6), in which 

The CD spectra of the complexes, [Co(ida)2] , [Co(ida) asp)] and [Co(asp)2] , should be compared with those of [Co(edta)] , [Co(eddams)] and [Co(edds)] , respectively, for the elucidation of absolute configurations. Their tentative assignments for the isomers of [Co(L-asp)2] were trans(N), cis(N)traits(OsO), and cis(N)-transiO O) in the order of dution, opposite to those made by Douglas et al. as to the two cw(N) isomers. An X-ray study was made by Oonishi et al. with a crystal of calcium bis(aspartato)cobaltate III), a reaction product of [Co(C03 3f and L-aspartate The structural analysis confirmed the formula Ca as(N)rrans(050)-[Co(L-asp)2] cis(N)/rans(060)-[Co(L-asp)2] 10 HjO assigned from the absorption and CD spectra. 

The stereochemistry of cobalt(III) complexes with 0,N,0-terdentate ligands of the linear type was studied by Okamoto et al. In a [Co(0,N,0-terdentate)2]-type complex four isomers,/ac-/rans(N), mer-trans(ti), A-c/ (N) and A-cis(N), are shown in Fig. 3.7. When L-alanine-N-monoacetic acid (L-H2alama) participates in coordination, the nitrogen donor atom of the L-alama is optically rtivated, and hence three isomers, RR, RS, and SS, are possible for each of the above rrans(N) and cis(N) forms. 

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Table 2.3 Bond distances (pm) in selected complexes with multidentate ligands.

Complexes with Multidentate Ligands Containing Anionic N-Donors... 

Trends in Potentials of Copper(ll/l) Complexes with Multidentate Ligands... 

Among complexes with multidentate ligands, a few lan-thanide(II) diketonates are known. [Eu(tmhd)2(dme)2], has been made by reaction of [Eul2(thf)2] with Kthd in thf, evaporation and crystallisation from DME [Sm(tmhd)2(dme)2] is made by a similar route. 

Slow isotopic exchange of the central ion in various square-planar copper(ii) complexes with multidentate ligands has also been studied, with special reference... 

Lanthanide Complexes with Multidentate Ligands Lanthanide Oxide/Hydroxide Complexes Lanthanides Coordination Chemistry Solvento Complexes of the Lanthanide Ions Trivalent Chemistry Cyclopentadienyl. 

Lanthanides in Living Systems Lanthanides Coordination Chemistry Lanthanides Luminescence Applications Lmninescence Lanthanides Magnetic Resonance Imaging Lanthanide Oxide/Hydroxide Complexes Carboxylate Lanthanide Complexes with Multidentate Ligands Rare Earth Metal Cluster Complexes Supramolecular Chemistry from Sensors and Imaging Agents to Functional Mononuclear and Polynuclear Self-Assembly Lanthanide Complexes. 

AUcyl Lanthanide Alkoxides Lanthanide Complexes with Multidentate Ligands Lanthanides Luminescence Apphcations. 

Lanthanide Complexes with Multidentate Ligands Supramolecular Chemistry from Sensors and Imaging Agents to Functional Mononuclear and Polynuclear Self-Assembly Lanthanide Complexes. 

Gadolinium ions are highly toxic in their hydrated form [Gd(H20)g] +. In vivo, Gd + ions compete with calcium ions and block the reticuloendothelial system. To avoid this toxicity, gadolinium is complexed with an organic thermodynamically stable matrix, (see Lanthanide Complexes with Multidentate Ligands, Organometallic Chemistry Fundamental Properties, Lanthanides Coordination Chemistry) In addition, ligands that allow coordination sites for one (or more) water molecule(s) ate preferred since they increase... 

References to kinetic studies of the displacement of a metal cation from its complexes with multidentate ligands are listed in Table 30. 

In this case the radical coupling of the benzyl radicals competes apparently successfully with the recombination. Co(IEI) complexes with multidentate ligands which prevent also a facile decay of Co(II) complexes show similar photoproperties [94]. An important example for this behavior is methylcobalamin [4]. 

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