Pulsed-laser photochemical study of tris(1,20-phenanthroline)chromium(III) ion in acidic and alkaline aqueous media

Journal Article · Wed Dec 03 04:00:00 EST 1986 · Inorg. Chem.; (United States)

DOI:https://doi.org/10.1021/ic00245a008· OSTI ID:6720664

Lilie, J; Waltz, W L; Lee, S H; Gregor, L L

The photochemistry and photophysics of tris(1,10-phenanthroline)chromium(III) ion, Cr(phen)/sub 3//sup 2 +/, following pulsed-laser excitation at 347 nm, have been studied in deaerated acidic and alkaline aqueous media (pH 3.0-11.1) at room temperature by using conductivity and visible optical detection methods. The lifetimes of the lowest doublet excited state(s) from which is derived the major portion of the photochemistry are little affected by changes in pH as monitored by emission and excited-state absorption nor are the initial intensity levels of these phenomena noticeably altered by pH changes. Alterations in pH do have significant effects on the conductivity signals, which correlate to photoaquation. Conductivity studies for natural pH (ca. pH 7.1) provide evidence for a ground-state intermediate with a pK/sub a/ value around 7. In basic media, an apparent single stage of conductivity occurs, and the values of the observed rate constant and the resulting overall change in conductance are dependent upon the concentration of hydroxide ion. The quantum yield for aquation at the highest pH of 11.1 is determined as 0.08 (+/-20%). By contrast, photochemical reaction in acidic media is found to be very much reduced relative to that occurring in alkaline solutions. A mechanism, incorporating a six-coordinate, monodentate phenathroline intermediate, is proposed, and it is used to discuss the occurrence of photoracemization and to compare the behavior of Cr(phen)/sub 3//sup 3 +/, where bpy designates the 2,2'-bipyridine ligand.

• Research Organization: Univ. of Saskatchewan, Saskatoon
• OSTI ID: 6720664
• Journal Information: Inorg. Chem.; (United States), Journal Name: Inorg. Chem.; (United States) Vol. 25:25; ISSN INOCA
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
140505 -- Solar Energy Conversion-- Photochemical
Photobiological
& Thermochemical Conversion-- (1980-)
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
AROMATICS
AZAARENES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISTRY
CHROMIUM COMPLEXES
COMPLEXES
DATA
EFFICIENCY
ENERGY LEVELS
EXCITED STATES
EXPERIMENTAL DATA
GROUND STATES
HETEROCYCLIC COMPOUNDS
INFORMATION
KINETICS
LASERS
LIFETIME
MEDIUM TEMPERATURE
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PH VALUE
PHENANTHROLINES
PHOTOCHEMICAL REACTIONS
PHOTOCHEMISTRY
PULSE TECHNIQUES
QUANTUM EFFICIENCY
REACTION INTERMEDIATES
REACTION KINETICS
TRANSITION ELEMENT COMPLEXES