Infrared Spectra of RuTPP, RuCOTPP, and Ru(CO)₂TPP Isolated in Solid Argon

Abstract

Infrared spectra of unstable species such as CO-free ruthenium tetraphenylporphyrin RuTPP and RuCOTPP (species with vacant coordination sites) isolated in solid argon at 8 K have been recorded. Selective deposition conditions allow the isolation of either RuTPP and RuCOTPP or RuCOTPP and Ru(CO)2TPP. This depends on the preparation conditions of the sample. A specific Ru-CO bending mode has been characterized at 590.1 cm(-1) for Ru(CO)2TPP. The behavior of each vibrational mode of RuTPP, RuCOTPP, and Ru(CO)2TPP has been analyzed. Modes such as gamma8 at 721.3 cm(-1) (out-of-plane stretching mode gamma(Cbeta-H)sym) and nu41 at 1342.8 cm(-1) (nuCalpha-N coupled with deltaCalpha-Cm) reflect the charge transfer in the porphyrin. Indeed, the addition of one or two CO ligands to RuTPP reduces the charge transfer between the metal center and the porphyrin, which appears as an increase in the frequency of the nu41 mode and in a decrease in that of the gamma8 mode.

Phosphate group effects upon the equilibrium of iron(III) meso-tetrakis (4-N-methylpyridiniumyl) porphyrin in aqueous solution

“…Optical absorption spectroscopy has been also successfully used in the assignment of penta-and hexacoordinated iron species [6][7][8]. Infrared spectroscopy is also a useful technique to monitore metal ligand coordination in metaloporphyrin systems [9][10][11]. Finally, the present results suggesting phosphate coordination to iron at low pH are important to complete and correct our previous results [4] where the involvement of the buffer in metal coordination was not, erroneously, considered.…”

Ultrafast Vibrational Dynamics of CO Ligands on RuTPP/Cu(110) under Photodesorption Conditions

“…This, in turn, would strengthen the C-O stretch bond and increase its stretch frequency. Indeed, the C-O stretch frequency of 1957 cm −1 , as seen in Figure 2b is higher than the 1951.1 cm −1 observed for CO-RuTPP in an Ar matrix at 8 K [33], and the 1944 cm −1 observed in vacuum at 293 K [34]. The blueshift of 13 cm −1 corresponds to about 2% increase of 2π* occupation [35,36].…”

In Situ Surface-Enhanced IR Absorption Spectroscopy on CO Adducts of Iron Protoporphyrin IX Self-Assembled on a Au Electrode

“…It is well-known from previous study on bulk-phase metalloporphyrin complexes that Fe II PP can form both mono- and biscarbonyl adducts of iron and ruthenium porphyrins. , The band frequency falls between ca. 1920−1975 cm -1 for the former and 1990−2050 cm -1 for the latter, and the frequency depends on the kinds of central metal ions, the trans base ligands, and the peripheral structures of the porphyrins .…”

“…Before the reacquisition, the potential was reset to −0.2 V in the presence of CO-saturated 0.1 M HClO 4 for 10 min followed by bubbling Ar to purge solution CO for 60 min. For bulk phase coordination reactions of other iron porphyrin molecules, the coordination constant of a monocarbonyl adduct is higher than its corresponding biscarbonyl adduct; as a result, the five-coordinate monocarbonyl adduct will convert to the six-coordinate biscarbonyl adduct with increasing CO pressure, 9a, and the opposite process will take place with decreasing CO pressure. For the surface CO coordination to an FePP adlayer at a Au electrode, at least in the time domain of the measurement, the purging of solution CO does not cause a significant reduction in the IR bands for these two species for the same electrode, which is suggestive of rather strong coordination affinity of CO to the FePP adlayer on the Au electrode.…”