Chromophore chelate

These reactions generate a single reactive site and occur via 15e, 16e, 17e, or 18e intermediates (6-8). One of our goals was to examine the photochemical behavior of complexes that contain an unsaturated chelate chromophore. Photofragmentation of these systems might lead to two reactive centers, either on the ligand or metal. This could produce intermediates that exhibit novel chemistry. 

The fluorescence and absorption of chelating chromophores and fluorophores is modified upon ion chelation. 

The Perturbing Chelate Chromophore System (B). The chelate system B may be considered effectively as three separate chelate chromophores indexed by I such that I = 1,2,3. Each individual chelate is considered to have a gound state < > and two electric dipole allowed (from the ground state ) excited states (fi, <1, so that the moment representation becomes... 

From a normal coordinate treatment of the IR spectrum of Fe(GMI)3, Nakamoto 728) concluded that the concept of group frequencies, as used above, may not be very appropriate for the conjugated chelate chromophore because of a strong couphng between various vibrational modes. The assignment of (weak) bands at 745, 515 and 501 cm-i to intermixed Fe—N and N—CHg stretches and the reported Fe—N force constant of 4.7 X 10 dyne/cm, seem surprisingly high. 

E. Circular Dichroism. The siderophores studied herein contain one bidentate ligand mounted on an optically active substituent, namely, threonine or its oxazoline. Th is the particular type of coordination isomer considered by Corey and Bailar (17) could result in a chelate chromophore which is capable of rotation of plane polarized li t. 

The complexes on surface of chelate-functionalized silica often include ligands available in solution in the coordination sphere. Use of a chromophore reagent as a ligand leads to the formation of colored mixed ligand complexes (MLC). The phenomena can be used as a basis for developing test-systems for visual determination of microquantities of inorganic cations in water. 

The discovery of crown ethers and cryptands in the late sixties opened new possibilities of cation recognition with improvement of selectivity, especially for alkali metal ions for which there is a lack of selective chelators. Then, the idea of coupling these ionophores to chromophores or fluorophores, leading to so-called chromoionophores and fluoroionophores, respectively, emerged some years later l9) As only fluorescent probes are considered in this chapter, chromoionophores will not be described. 

Structurally these compounds combine a eight-coordinate tetracarboxylate chelating site with stilbene chromophores. Of the six dyes proposed in Ref. 121 only Indo-1 leads to a short-wavelength fluorescence shift when bound to Ca2+. It is also the probe with the smallest D-A interactions as revealed by the shortest wavelength of fluorescence of the free ligand. As a consequence, the decrease of the electron density of the nitrogen binding site is not sufficient to break completely the interaction with Ca2+ in the excited state and the spectrum is considerably blueshifted. 

In our NMR studies 143,147,148,322-324) of amine and other adducts of Ni[R-dtp]2 complexes neat amines were employed in order to eliminate variations in extent of association (H-bonding) of the amines, to permit observation of NH proton shifts, and to maximize the concentration of the preferred adduct. The use of high concentration of primary amines in solutions with Ni[R-dtp]2 complexes can lead to products other than those expected, e.g., with aliphatic diamines, the R-dtp anion salts of f/zs(diamine)nickel(ll) chelates are obtained ). Furlani and co-workers ) have shown that Ni-(ethyl-dtp)2 reacts with n-butyl amine to yield complexes containing the NiS2N4 chromophore, presumably with monodentate ethyl-dtp. In all work with adducts it is necessary to assure that the complexes, adduct molecules and solvent systems are anhydrous. A number of authors 132,284,295,329) shown that Ni[ R-dtp ]2 complexes decompose when in contact with water. 

---