Tris complex, with

Few Fe(III) complexes have been reported with dithioaliphatic or dithio-aromatic ligands. The deeply colored tris-complexes with the FhDta" and BzDta- ligands have been reported to contain a pseudooctahedral Fe(III)S6 chromophore (111). They all are low spin as expected from the high field strength of the ligands. The M5ssbauer spectra of these compounds were recorded (111). Attempts to prepare the Fe(PhDta)2Cl complex by the reaction of the tris complex with HG failed. 

Right) Luminescence lifetimes of tris and ternary Nd111 complexes as a function of the fluorinated radical chain length. Filled and opened triangles stand for tris complexes with benzoylacetonate and thienylacetonate derivatives, respectively filled and opened circles for the corresponding ternary complexes formed with phen. 

Trimethyldipyrromethane (dpm) yields the low-spin six-co-ordinate tris-complex with iron(m). Strong ligand-field bands in this complex are consistent with the presence of a trigonal distortion and highly covalent metal ligand bonds.217 The complex [Fe(pbz), ]Cl, [pbz = 2-(2 -pyridyl)benzimidazole] has also been reported.214... 

Tris-chelate complexes exist in enantiomeric configuration A and D about the metal atom, and when the chelating ligand is unsymmetrical, there are also geometrical isomers, cis and trans. Each geometrical isomer exists in enantiomeric forms thus there are four different molecules. In the case of tris complexes with symmetrical ligands, the process of inversion (interconversion of enantiomers) is important. When the metal ions are of the inert type, it is often possible to resolve the complex then the process of racemisation can be followed by measurement of optical rotation as a function of time. Possible pathways for racemisation fall into two broad classes those without bond rupture and those with bond rupture. 

Chelate complexes. Chelate rings can be formed by pyridines containing -substituents such as carboxyl or CH=NR. Important bicyclic chelating agents are 2,2-bipyridyl 68 (R = H), o-phenanthroline 69 and 8-hydroxyquinoline 70, which all form bis and tris complexes with many metals <1994CSR327>. This type of complex formation has many analytical applications. Overlap between the d-orbitals of the metal atom and the pyridine -orbitals is believed to increase the stability of many of these complexes. Steric effects can hinder complex formation as in 68 (R = Me). 

Treatment of the tris(dialkyldithiocarbamato)iron(III) complexes in benzene with a controlled amount of concentrated hydrohalic acid affords the black bis(ligand) complexes [FeX(S2CNR2)2] (X = Cl, Br or I).306 For X = Cl the complexes may also be prepared by irradiation of the tris-(ligand) complex in a halogenated solvent. This free radical reaction is believed to proceed via excited-state labilization of one ligand followed by attack of solvent.307 Analogous complexes of pseudohalide ions (X = NCO, NCS- or NCSe ) have been obtained from reaction of the parent tris complex with the appropriate Ag+ salt.380 Representative complexes of this class have been shown by X-ray diffraction methods to have square pyramidal structures (71) in which the sulfur atoms of the two bidentate ligands comprise the basal plane (Fe—S 2.228 2.30 A) with the halide ion in the apical position (Fe—Cl 2.26-2.28 A).309 310 In the cases examined the metal atom sits 0.6 A out of the mean S4 plane in the direction of the apical halide ion. 

Reaction of 0s04 with catechol or substituted catechols Rcat in chloroform yields the deep blue diamagnetic Os(Rcat)3 species (Rcat = catechol, 4-rerf-octyl-, 4-terr-butyl-, 3,5-di-ferf-butyl-catech-ol).486 X-Ray crystal structures of Os(cat)3 and of the tris complex with 3,5-di-terf-butylcatechol show these to have D3 symmetry the Os—O distances fall within the range 1.947 to 1.985 A (mean 1.960 A) and the C—O distances are between 1.30 and 1.35 A the catecholato (02C6H4 or 02C6H2) rings are essentially planar.666 For Os(cat)3, IR, Raman, HNMR and electrochemical data were obtained the latter showed two one-electron reversible reductions, presumably to [Os(cat)3] and [Os(cat)3]2-. The diamagnetism of these formally osmium(VI) species probably arises from the distortion from octahedral to Z>3 symmetry.486... 

Dipicolinic acid or 2,6-pyridinedicarboxylic acid (H2dipic), an excellent chromophore for Eu(III) and Tb(III) sensitization, forms stable tris complexes with RE(III) ions, [RE(dipic)3] [78], The Eu(III) and Tb(III) complexes are very bright red and green emitters with quantum yields of 12 and 21%, respectively. All of their RE(III) analogs are isostructural and their second order NLO activities were reported. In the complexes, the RE(III) ions are coordinated by three tridentate dipic with a symmetry close to D3, CN = 9 [79],... 

In order to obtain neutral tris complexes with the lanthanide(III) ion surrounded by three tridentate ligands to form a nine-coordinated geometry, an amide is introduced to the 2-position of 8-hydroxyquinoline, affording the tridentate derivatives 12,12-Br, and 12-Br2 [31]. In these tris complexes, the lanthanide(III) ion is shielded against intrusion by the solvent molecules into the first coordination sphere. As revealed by X-ray crystallography, the three stranded ligands coordinate to the lanthanide(III) ion in a helical fashion, leading to a coordination... 

Further examples of tris complexes with tn rings substituted at the 2 position include 2-hydroxy-l,3-diaminopropane (87), 2-bromo-l,3-diaminopropane (87), and 2,2-dimethyl-l,3-diaminopropane. (88)... 

Polynuclear iron(II) and cobalt(III) oximehydrazonates have arisen from the template macrocyclization of the initial nonmacrocyclic tris-complexes with polydentate ligands resulting from the condensation of the corresponding diketones and their monooximes with hydrazine [193]. The tris-complexes formed have... 

Macrobicyclic binuclear iron(II) oximehydrazonates were synthesized by encapsulation of initial nonmacrocyclic tris-complexes with boron- and tin-containing Lewis acids and by direct template reactions on the Fe + ion (Scheme 89). 

Figure 12. Differences in destabilization energies for the low- (1-3) and high-spin (4-6) tris-complexes with TP and TAP geometries at a = 35° [1 and 4], 38.5° [2 and 5], 45° [3 and 6] as a function of the d-electron number. The x-bonding effect is not taken into account [93].

The most stable oxo-complexes are chelate compounds. Gallium and indium form tris- -diketone complexes, soluble in alcohol and benzene, and structurally similar to those of aluminium (Fig. 155). Gallium and thallium form trioxalato compounds like the oxalato-aluminates MJ[Ga ( 304)3]HgO. All the metals form tris-complexes with oxine (Fig. 156). 

The dipicolinic acid platform has proven to be extremely versatile, leading to numerous applications of its tris-complexes with Eu and Tb, in particular in analytical and bioanalytical chemistry (see Section 2.5 for photophysical properties and Section 6.2 for bioanalytical applications). As a consequence, researchers have invented ways of modulating the photophysical properties, principally by introducing substituents on the para position of the pyridine ring, a relatively easy synthetic procedure. Simple substituents (e.g.. Cl, Br, NH2, NHCOCH3) are introduced by substitution of the hydroxyl function of chelidamic acid under... 

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