TIME-RESOLVED RESONANCE RAMAN-SPECTROSCOPY AT LOW-TEMPERATURE - THE EXCITED-STATE METAL-METAL STRETCHING FREQUENCY OF RH-2(TMB)(4)(2-DIMETHYL-2,5-DIISOCYANOHEXANE)() (TMB = 2,5)
Rf. Dallinger et al., TIME-RESOLVED RESONANCE RAMAN-SPECTROSCOPY AT LOW-TEMPERATURE - THE EXCITED-STATE METAL-METAL STRETCHING FREQUENCY OF RH-2(TMB)(4)(2-DIMETHYL-2,5-DIISOCYANOHEXANE)() (TMB = 2,5), Inorganic chemistry, 37(19), 1998, pp. 5011-5013
The time-resolved resonance Raman spectrum of the short-lived triplet
(d sigmap sigma) excited state of Rh-2(TMB)(4)(2+) (TMB = 2,5-dimethy
l-2,5-diisocyanohexane) was obtained by lowering the temperature of a
3:1 ethanol/methanol solution until the excited-state lifetime became
much greater than the width of the pulsed laser excitation source. The
metal-metal stretching frequency is 151 cm(-1) in the excited triplet
state, as compared to 50 cm(-1) in the ground state. The diatomic har
monic force constants derived from these frequencies are in a 9.12:1 r
atio (excited state/ground state), consistent with the simple molecula
r orbital description that predicts that the Rh-Rh bond order is great
er in the excited state than in the ground state. A comparison of Rh2(
TMB)42+ and Rh(2)b(4)(2+) (b = 1,3-diisocyanopropane) Raman data indic
ates that the nature of the bridging ligand considerably affects the g
round- and excited-state metal-metal stretching frequencies and that t
he population of the p sigma orbital may have very little effect on th
e bonding in the excited triplet state.