Synthesis and photobehavior of chromium(III) and rhodium(III) complexes of the macrocyclic ligand C-meso-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane

Abstract

and MY"*] » ML1 234567*] are met. At this point, Md will approach the value of k-L, where M is the limiting rate of dissociation of L"4" from Ru(CN)5L(3"'i)•. Similarily, as [Ym+] is decreased, the observed rate constant approaches the rate of dissociation, M> of Y"4" from Ru(CN)5Y(3~'"h The expression in eq 5 is consistent with the observed dependence of the rate on [Ym+] for the substitution reactions in this study. With k_L for the complexes with nitrogen heterocycles being greater (Table I) than the corresponding rate constant for the dimethyl sulfoxide complex, fcobsd increases to a limiting value (Figure 1) with increasing [N^SO],In the substitution reactions of the dimethyl sulfoxide complex, an increase in [Ym+] results in a decrease in kobsi to a limiting value.Rate constants and activation parameters have been reported for formation and dissociation reactions of the analogous Fe-(CN)5L(3~',,~complexes. [1][2][3][4][5]14 The enthalpies of activation associated with M are similar for the two systems while the entropy values are slightly lower (5-10 cal K"1 mol"1) for the ruthenium complexes. The decreased entropies of activation are suggestive

Cr(III)-HMC (HMC = 5,5,7,12,12,14-Hexamethyl-1,4,8,11-tetraazacyclotetradecane) Alkynyl Complexes: Preparation and Emission Properties

“…These structured emissions are believed to be of vibronic origin, as noted in other Cr­(HMC) and Cr­(cyclam) complexes . The emission of cis -[Cr­( rac -HMC)­Cl 2 ]Cl at 77 K is also structured, similar to 1a and 1b in glass, albeit at lower wavelengths …”

Effects of Steric Constraint on Chromium(III) Complexes of Tetraazamacrocycles, 2. Comparison of the Chemistry and Photobehavior of the trans-Dichloro- and trans-Dicyano- Complexes of Cyclam, 1,4-C2-Cyclam, and 1,11-C3-Cyclam

“…Photophysical data for the trans -[Cr(N 4 )(CN) 2 ] + complexes (where N 4 = cyclam, 1,4-C 2 -cyclam, or 1,11-C 3 -cyclam) are summarized in Table and Figure . As demonstrated in Figure , the 1,4-C 2 -cyclam and 1,11-C 3 -cyclam complexes are dominated by the 0−0 band in contrast to the cyclam complex, , which shows substantial vibronic structure. This probably reflects the lower symmetry of these complexes as discussed above.…”

“…Complexes of the trans -[Cr(N 4 )X 2 ] n + (where N 4 = ammine or polydentate amine ligands or their combination and X = Cl - , F - , CN - , − or NH 3 ) type have a rich photochemistry, and the study of these complexes has offered insights into photochemical mechanisms . Of particular interest are studies that demonstrate the effect of geometric distortion and constraint on the photobehavior of the complex. ,,− We recently reported the chemistry and photobehavior of a complex of the constrained ligand 1,4-C 2 -cyclam (Figure ) …”

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

“…An interesting exception is trans-Rh(cyclam)(CN) 2 + , which is photoinert to ligand substitution [122,124,125]. Here the 3 T 1g (O h ) splits into 3 E g and 3 A 2g (D 4h ) levels, with the 3 A 2g being the lower energy (see also Section 4.3).…”