Photochemistry of complex ions. XII. Photochemistry of cobalt(III) acidoammines

Abstract

The photolysis of CO(NH&~+, CO(NH&(H~O)~+, CO(NH~)~F*+, Co(NH8)sC12+, frans-Co(en)2C12+, and frans-Co(cyclam)Cl2+ in the wavelength region of the ligand field bands is reported, using a continuous wave Argon laser as light source. At 488.0 nm, quantum yields for Co(I1) production by redox decomposition are negligible compared to those for ammonia and X-aquation, which range from For the acidoammines, + N H~ dominates over +x-, and in the case of the chelate complexes, only chloride aquation occurs; frans-Co(en)zC12+ is 72 stereoretentive to give the trans-chloro aquo complex, while Co(cyclam)C12+ photoaquates with 100% stereoretention. It is believed that the low quantum yield values reflect enhanced radiationless deactivation rates, relative to the corresponding Cr(II1) complexes, rather than reduced excited state chemical reactivities. The qualitative photochemistry partly conforms to the photolysis behavior of Cr(II1) complexes but differs in detail ; for example, the stereochemistry of the products indicates that important differences in excited state reaction mechanisms are present.to 5 x he photochemistry of Co(II1) coordination com-

Photochemistry of Biologically Important Transition Metal Complexes. I. Cyanocobalamin and Related Corrin Complexes of Rhodium(III)

“…The low quantum yield of photoaquation of cyanocobalamin means then that either the deactivation of the excited corrin singlets leads to the lowest excited LF singlet which does not undergo efficient intersystem crossing to the reactive LF triplet or, more likely, the population of the reactive triplet is very effective, however, its deactivation does not only occur by the photoreaction but also by an efficient radiationless transition to the ground state. These explanations have been advanced to explain the low quantum yields of photoaquation which have been obtained upon LF excitation of Co(III) ammines [28,29].…”

Kinetic and Mechanistic Observations on the Photoinduced Isomerization Reaction of Organometallic Chalcones: A Steady State and Flash Photolysis Study

“…The cyrhetrenyl, ferrocenyl and cymantrenyl chalcones were prepared and characterized in previous work . Aldrich CH 3 OH, CH 3 CN and CH 2 Cl 2 chromatographic grade and ultrahigh purity N 2 were used as received.…”

“…CW irradiations at either 350 nm or 300 nm were carried out using the appropriate Rayonet lamps. The light intensities at 300 nm ( I 0 =9.61×10 −5 Einstein l −1 min −1 ) and 350 nm ( I 0 =1.10×10 −4 Einstein l −1 min −1 ) were, respectively, determined with the secondary actinometer [Co(NH 3 ) 5 Br](ClO 4 ) 2 and a calibrated photocell. Solutions were deaerated with streams of ultra‐high purity N 2 .…”

Ultrafast Excited-State Dynamics of Ligand-Field and Ligand-to-Metal Charge-Transfer States of CuCl42– in Solution: A Detailed Transient Absorption Study

“…LMCT excitation of iron­(III) chloride and bromide complexes in water and alcohols results in the iron-halogen bond breaking with the formation of iron­(II) complexes and halogen atoms. − The photodissociation process is often followed by a ligand substitution reaction. In aqueous solutions, the coordinated ligand can be photochemically substituted by the water molecule (the photoaquation reaction). − For example, Fehlner and Turner proposed that aqueous NiLCl 2 , where L = NH 2 (CH 2 ) 2 NH­(CH 2 ) 3 NH­(CH 2 )­NH 2 , upon LMCT excitation forms NiL­(H 2 O) 2 . The femtosecond studies of metal complexes with organic ligands have revealed another relaxation pathway of LMCT excited states, such as highly efficient internal conversion and intersystem crossing into low-lying d–d states followed by their relaxation into the ground state (GS) on femto- and picosecond time scales. − The femtosecond studies of aqueous ferric hexacyanide, [Fe­(CN) 6 ] 3− , revealed two main relaxation channels following LMCT excitation: CN – elimination followed by aquation to form [Fe­(CN) 5 H 2 O] 2– and internal conversion into the vibrationally hot ground electronic state. , …”