Metal complexes, anion sensing

Transition metal complexes with 2,2 -bipyridine ligands in anion-selective recognition and optical/electrochemical sensing 96CC689. 

The common problems with those metallomicelles may be summarized as follows (1) Most of these complexes were prepared in situ and often were not isolated. Hence, the intended structures of the metallomicelles in solution or in the solid state were not verified. (2) The metal complexes in solution were not identified or characterized in rigorous thermodynamic senses by potentiometric pH titration, etc. The complexation constants and possible species distribution at various pH s were totally unknown. (3) Possible catalytically active species L-Mn+—OH were not identified by means of the thermodynamic pvalues. Those described were all obtained merely in kinetics. (4) The product (phosphate anion) inhibition was not determined. Accordingly, it often was not clear whether it was catalytic or not. (5) Often, the substrates studied were limited. (6) The kinetics was complex, probably as a result of the existence of various species in solution. Thus, in most of the cases only pseudo-first-order rates (e.g., with excess metal complexes) were given. No solid kinetic studies combined with thermodynamic studies have been presented. It is thus impossible to compare the catalytic efficiency of these metallomicelles with that of the natural system. Besides, different... 

The receptor 67 [54] shows the sensing of F in DMSO. Upon addition of F to the solution of receptor 67 two bands at 323 and 525 nm decreased and a new band at 652 nm appeared. Furthermore, the color of the solution changed from red-pink to pale purple. These spectral changes were ascribed to the formation of a 1 1 adduct between the metal complex and F anion, in which F anion bound two dipyrrolylquinoxaline units (fC=54,000 M ) Receptor 67 was also studied electrochemically by cyclic voltammetry. A clearly reversible redox signal was observed at 160 mV (vs SHE), which was assigned to the Co(III)/Co(II) reduction. The addition of F led to a complete disappearance... 

Troster, T., 2003. Optical studies of non-metallic compounds under pressure. In Gschneidner Jr., K.A., Biinzli, J.-C.G., Pecharsky, V.K. (Eds.), Handbook on the Physics and Chemistry of Rare Earths, vol. 33. Elsevier, Amsterdam, pp. 515-589 (chapter 217). Tsukube, H., Shinoda, S., 2002. Chem. Rev. 102, 2389. Tsukube, H., Shinoda, S., 2006. Near infrared emissive lanthanide complexes for anion sensing. ICFE 6 Conference, Wroclaw, September 4-9, 2006, paper AI-5. 

Screening of an impressive series of polymers derived from different bulky methacrylate esters, e.g., 42 (Chart 8), and using a variety of chiral ligands has revealed the scope of the process of forming helical poly(methacrylate ester)s and their applicability in, for example, the separation of chiral compounds.151 These polymers were prepared not only by anionic polymerization, but also by cationic, free-radical, and Ziegler—Natta techniques. Recently, Nakano and Okamoto reported the use of a co-balt(II)—salophen complex (43) in the polymerization of methacrylate ester 41.155 The free-radical polymerization in the presence of this optically active metal complex resulted in the formation of an almost completely isotactic polymer with an excess of one helical sense. 

Let s consider the oxidative addition of Eq. (1). Because A and B groups become anion and the d electron number of the metal center decreases by 2 in a formal sense, the charge-transfer should take place from the occupied d orbital of the metal center to the o anti-bonding orbital of the A-B bond. Actually, Hoffmann and his collaborators previously indicated the importance of the charge-transfer from the occupied d orbital to the o anti-bonding orbital in the oxidative addition of the C-H bond to a transition-metal complex... 

Another class of mixed-metal anion receptors has been investigated which possess redox reporter groups based on two different metal complexes. This enables the quahtative comparison of their comparative anion-sensing abih-ties. Macrocycles 35 and 36 combine the Ru (bpy)3 moiety with a bridging ferrocene or cobaltocenium imit [29]. Electrochemical experiments in acetonitrile solution revealed that the Ru VRu redox potential was insensitive to anion binding, whereas the ferrocene/ferrocenium (in 35) and cobal-tocene/cobaltocenium (in 36) redox couples were shifted cathodically (by 60 mV and 110 mV respectively with chloride). However, the first reduction of Ru°(bpy)3, a Hgand-centred process based on the amide substituted bipyridyl, was also found to imdergo an anion induced cathodic shift (40 mV and 90 mV with chloride for 35 and 36, respectively). 

The spectroscopic and redox properties of Ru°(bpy)3 have allowed this metal complex to be used for combined optical and electrochemical sensing of anions without the need for additional chromophores or luminophores. 

Optical Anion Sensing Using Reporter Groups Based on Other Transition-Metal Complexes... 

---