Photochemistry of (2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene)copper(II): participation of copper(II) hydrides
The photochemistry in acidic methanol and the relevant thermochemistry of (2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene)copper(II) (ligand abbreviations are 2,3,9,10-Me/sub 4/-(14)-1,3,8,10-tetraeneN/sub 4/ or L in this work) have been investigated. UV photolysis results in the rapid formation of a transient identified as Cu(2,3,9,10-Me/sub 4/-(14)-1,3,8,10-tetraeneN/sub 4/)/sup +/. A minor fraction of the transient is produced in t < 10 ns and a major fraction in the microsecond time domain via a second-order process (k = (5.7 +/- 0.3) x 10/sup 7/ M/sup -1/ s/sup -1/) that involves the reaction of solvent radicals (CH/sub 2/OH) with the copper(II) macrocycle. In perchlorate media, (ClO/sub 4//sup -/) > 10/sup -3/ M, a first-order isomerization followed in milliseconds (k = (2.0 +/- 0.3) x 10/sup 3/ s/sup -1/). Cu(2,3,9,10-Me/sub 4/-(14)-1,3,8,10-tetraeneN/sub 4/)/sup 2 +/ then undergoes slow decay by competitive pathways to produce H/sub 2/ and Cu/sub solv//sup +/. The product quantum yields (10/sup -3/ < phi/sub Cu/sup +/solv/ < 10/sup -2/; 10/sup -4/ < phi/sub H/sub 2// < 10/sup -3/) depend on light intensity, acid concentration, and the concentration of the copper(II) macrocycle. The production of hydrogen is postulated to occur via a copper(II) macrocycle in acid solution. The thermal properties relevant to an interpretation of the photochemistry were as follows: (1) There is a dependence on solvent of E/sub 1/2/ for the Cu/sup II/L/Cu/sup I/L couple (varies from -0.02 V in CH/sub 2/Cl/sub 2/ to -0.62 V vs. SCE in H/sub 2/O) and the CuL/sup 2 +/ electronic absorption spectrum. (2) The E/sub 1/2/ value for the ligand reduction at approx.-1.4 V vs. SCE shifts positively in acidic media until it overlaps the metal(II/I) couple. (3) The spectral properties of Cu(2,3,9,10-Me/sub 4/-(14)-1,3,8,10-tetraeneN/sub 4/)/sup +/ generated by coulometric reduction (n = 1.01) at -0.60 V vs. SCE in acetonitrile are lambda/sub max/ = 746 nm with epsilon approx. = 8 x 10/sup 3/ M/sup -1/ s/sup -1/. 24 references.
- Research Organization:
- Univ. of Notre Dame, IN
- OSTI ID:
- 5528643
- Journal Information:
- Inorg. Chem.; (United States), Journal Name: Inorg. Chem.; (United States) Vol. 24:3; ISSN INOCA
- Country of Publication:
- United States
- Language:
- English
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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400301 -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
400500* -- Photochemistry
ALCOHOLS
AROMATICS
AZAARENES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISTRY
CHLORINE COMPOUNDS
COMPLEXES
COPPER
COPPER COMPLEXES
COPPER COMPOUNDS
COPPER HYDRIDES
DATA
DECOMPOSITION
ELECTROMAGNETIC RADIATION
ELECTRON TRANSFER
ELECTRONIC STRUCTURE
ELEMENTS
EXPERIMENTAL DATA
HALOGEN COMPOUNDS
HETEROCYCLIC COMPOUNDS
HYDRIDES
HYDROGEN COMPOUNDS
HYDROGEN PRODUCTION
HYDROXY COMPOUNDS
INFORMATION
ISOMERIZATION
KINETICS
LIGANDS
METALS
METHANOL
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANOMETALLIC COMPOUNDS
OXYGEN COMPOUNDS
PERCHLORATES
PH VALUE
PHOTOCHEMICAL REACTIONS
PHOTOCHEMISTRY
PHOTOLYSIS
PHYSICAL PROPERTIES
RADIATIONS
REACTION INTERMEDIATES
REACTION KINETICS
SOLVATION
SPECTRA
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPLEXES
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
ULTRAVIOLET RADIATION
ULTRAVIOLET SPECTRA
VOLTAMETRY