Synthesis, spectroscopy, and photophysical behavior of mixed-ligand mono- and bis(polypyridyl)chromium(III) complexes. Examples of efficient, thermally activated excited-state relaxation without back intersystem crossing

Journal Article · Wed Jun 29 00:00:00 EDT 1988 · Inorg. Chem.; (United States)

DOI:https://doi.org/10.1021/ic00286a002· OSTI ID:5853486

Ryu, C K; Endicott, J F

A series of Cr/sup III/(PP)/sub x/X/sub 6-2n/ complexes have been prepared and characterized in which n = 1 or 2, PP = 2,2'-bipyridine or 1,10-phenanthroline, and X = NH/sub 3/, en/2, acac/sup /minus///2, CN/sup /minus//, or NCS/sup /minus//. The (/sup 2/E)Cr/sup III/(PP)/sub n/X/sub 6-2n/ excited states are much weaker oxidants than their (/sup 2/E)Cr(PP)/sub 3//sup 2+/ parents. The visible spectroscopy of the Cr/sup III/(PP)/sub n/X/sub 6-2n/ complexes is complicated by overlapping absorptions. A very prominent feature of these absorptions is a regular, relatively narrow band progression with energies independent of X. This progression is attributed to direct excitation into the triplet-/pi/* ligand manifold states, with the forbidden singlet-triplet transitions of the free polypyridyl ligand(s) being relaxed by spin-spin coupling in the Cr(III) complexes. The (/sup 2/E)Cr(III) lifetimes, /tau/(/sup 2/E), of these complexes in fluid and glass solutions are strongly temperature dependent but approach a limiting value at low temperatures: (/tau/(/sup 2/E))/sup /minus/1/ = k/sub r/ + k/sub nr//sup 0/ + A exp(/minus/E/sub a//RT), where k/sub r/ and k/sub nr//sup 0/ are the nearly temperature-independent radiative and nonradiative relaxation rate constants, respectively. The room-temperature lifetimes of the mixed-ligand complexes vary over a 30-fold range, and /tau/(/sup 2/E) is much smaller for these complexes than found for their Cr(phen)/sub 3//sup 3+/ and Cr(bpy)/sub 3//sup 3+/ parents. The range of lifetimes is not strongly temperature dependent since E/sub a/ = 33 /plus minus/ 2 kJ mol/sup /minus/1/ and A = (3.5 /plus minus/ 1.1) /times/ 10/sup 11/ s/sup /minus/1/ for the Cr/sup III/(PP)/sub n/X/sub 6-2n/ complexes (X ne CN/sup /minus//); for X = CN/sup /minus//, A /approx/ 7 /times/ 10/sup 12/ s/sup /minus/1/. 65 references, 8 figures, 9 tables.

• Research Organization: Wayne State Univ., Detroit, MI (USA)
• OSTI ID: 5853486
• Journal Information: Inorg. Chem.; (United States), Vol. 27:13
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
AMMONIA
EXCITED STATES
SYNTHESIS
CHROMIUM COMPLEXES
PHENANTHROLINES
PYRIDINES
EXPERIMENTAL DATA
AROMATICS
AZAARENES
AZINES
COMPLEXES
DATA
ENERGY LEVELS
HETEROCYCLIC COMPOUNDS
HYDRIDES
HYDROGEN COMPOUNDS
INFORMATION
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
TRANSITION ELEMENT COMPLEXES
400201* - Chemical & Physicochemical Properties