Ammonium based anion receptors

The selectivity and sensitivity of two colorimetric sensors based on the ruthenium complexes N719 [bis(2,2‘-bipyridyl-4,4‘-dicarboxylate)ruthenium(II) bis(tetrabutylammonium) bis(thiocyanate)] and ...

Reversible colorimetric probes for mercury sensing.

The molecular structure and dynamics of the photoexcited metal-to-ligand-charge-transfer (MLCT) state of [CuI(dmp)2]+, where dmp is 2,9-dimethyl-1,10-phenanthroline, in acetonitrile have been investigated by time-domain pump-probe X-ray absorption spectroscopy, femtosecond optical transient spectroscopy, and density functional theory (DFT). The time resolution for the excited state structural determination was 100 ps, provided by single X-ray pulses from a third generation synchrotron source. The copper ion in the thermally equilibrated MLCT state has the same oxidation state as the corresponding copper(II) complex in the ground state and was found to be penta-coordinate with an average nearest neighbor Cu−N distance 0.04 A shorter than that of the ground state [CuI(dmp)2]+. The results confirm the previously proposed “exciplex” structure of the MLCT state in Lewis basic solvents. The evolution from the photoexcited Franck-Condon MLCT state to the thermally equilibrated MLCT state was followed by femtosec...

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MLCT state structure and dynamics of a copper(I) diimine complex characterized by pump-probe X-ray and laser spectroscopies and DFT calculations.

Metal centered ligand field excited states: Their roles in the design and performance of transition metal based photochemical molecular devices

The role of transition metal complexes is overviewed for the iron, copper and chromium compounds, for which photoreactivity is of crucial environmental importance. Attention is paid to these complex systems, in which metal centres are photoreduced by organic matter under solar irradiation and re-oxidized by molecular oxygen, i.e. to the systems, that play a part in the environmental photocatalysis. The photoreduction is accompanied by simultaneous oxidation of organic matter, which plays a role of ligand and/or sacrificial electron donor. Under favourable conditions a complete photodegradation of the organic pollutants can be achieved. The general mechanisms are analysed and examples of different photocatalytic behaviours are presented in some details. The systems are more sophisticated due to concurrent generation of active oxygen species, such as the O 2 − , HO 2 , OH , H 2 O 2 , and HO 2 − , which are involved in the redox reactions of the photocatalytic cycling and influence the pollutant degradation. Beside the monometallic cycles, the mixed metal systems can function in nature. The cooperation between the photocatalytic cycles of two metals can abate diverse environmental pollutants, but their efficiency can be either higher or lower in comparison with that of the sum of single cycles.

Homogeneous photocatalysis by transition metal complexes in the environment

Stereochemistry of equatorial aquation in the ligand field photolysis of trans-dicyanotetraamminechromium(III)

Cyanopentaamminechromium(III). Synthesis, characterization, and aquation kinetics

Some new complexes of nickel(II) halides with N,N′-disubstituted thioureas

Thermal and photochemical aquation of some substituted acetatopentaamminechromium(III) ions

The ligand field photolysis of three trans-Cr(NH/sub 3/)/sub 4/(CN)X/sup z+/ ions, with X = H/sub 2/O, NCS/sup -/, and F/sup -/, has been studied in acidic aqueous solution (10/sup -3/ M HClO/sub 4/). These complexes are electronically unusual, in that the CH/sup -/ and X axial groups act in opposition on the splittings of the octahedral states and, moreover, are respectively ..pi..-acceptors and ..pi..-donors. In each case photoaquation of all three types of ligands is observed. For X = H/sub 2/O, trans ..-->.. cis photoisomerization is taken as a measure of water photoexchange. The total quantum yields are in the 0.2-0.4 range, virtually wavelength independent. Equatorial and axial reactivities are of comparable magnitude, their ratios being 0.32, 2.5, and 3.0 for X = H/sub 2/O, NCS/sup -/, and F/sup -/, respectively, upon irradiation of the long-wavelength maximum. This is consistent with the small energy separation between the lowest excited quartet states, /sup 4/E and /sup 4/B/sub 2/. The results are compared with the predictions of various photolysis models and are analyzed particularly in terms of excited-state sigma-and ..pi..-bonding changes. All three complexes phosphoresce from the lowest doublet state under photochemical conditions, with 20/sup 0/C lifetimes of 1.1, 30, and 0.2more » ..mu..s, respectively. Luminescence and photoreaction quenching by Cr(C/sub 2/O/sub 4/)/sub 3//sup 3 -/ have been investigated in the case of trans-Cr(NH/sub 3/)/sub 4/(CN)(NCS)/sup +/. The quantum yields for the three photoaquation modes decrease in parallel with emission and, upon complete doublet quenching, one-fourth of the photoreactivity remains unquenched. The proportion in ligand labilization is the same for both the unquenchable and the quenchable photochemistry.« less

Pietro Riccieri

Papers

Stereochemistry of equatorial aquation in the ligand field photolysis of trans-dicyanotetraamminechromium(III)

Cyanopentaamminechromium(III). Synthesis, characterization, and aquation kinetics

Some new complexes of nickel(II) halides with N,N′-disubstituted thioureas

Thermal and photochemical aquation of some substituted acetatopentaamminechromium(III) ions

Ligand field photochemistry of trans-tetraamminechromium(III) complexes with one strong-field and one weak-field axial ligand