Correlations between Raman frequencies and structures for planar and nonplanar metalloporphyrins
- Sandia National Labs., Albuquerque, NM (United States)
- Univ. of California, Davis, CA (United States); and others
Resonance Raman spectra were obtained for two series of metalloporphyrins, and frequencies of structure-sensitive Raman lines are correlated with structural changes in the porphyrin macrocycle. In the first series, metal derivatives of tetracyclohexenyltetraphenylporphyrin (TC{sub 6}TPP), the porphinato core size is varied by varying the metal (Ni < Co < Cu), causing little change in the planarity of this nonplanar porphyrin. In the second series, nickel complexes of tetracyclopentenyl-, tetracyclohexenyl-, and tetracycloheptenyltertraphenylporphyrin (NiTc{sub x}TPP, where x = 5-7), the size of the alky ring at the {beta}-carbon positions of the pyrrole rings is varied. In the NiTc{sub x}TPP series, the porphyrin macrocycle becomes significantly more nonplanar as the alkyl ring becomes larger and steric crowding increases. As a consequence of the increasing nonplanarity, the porphyrin core contracts. Correlations between Raman frequencies and structural parameters, including core size and C{sub {alpha}}-N-C{sub {alpha}} angle (obtained from molecular mechanics calculations), are found for both series of porphyrins. These new correlative relationships are compared to similar relationships previously observed for metal octaalkylporphyrins, metal tetraphenylporphyrins, and a series of Ni octaalkyltetraphenylporphyrins. Most importantly, by comparing the metal series (Ni, Co, Cu, Zn, etc.) for differing porphyrin ligands, the authors find a trend toward weaker frequency dependence on core size for the more nonplanar porphyrins. Thus, the applicability of this useful structural correlation is extended to both planar and nonplanar porphyrins. Finally, the differences between these correlative relationships are traced to more fundamental (Badger`s rule) relationships between vibrational frequencies and the length of bond contributing to the total potential energy of the vibrational modes corresponding to the structure-sensitive Raman lines.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 450860
- Journal Information:
- Inorganic Chemistry, Journal Name: Inorganic Chemistry Journal Issue: 10 Vol. 33; ISSN 0020-1669; ISSN INOCAJ
- Country of Publication:
- United States
- Language:
- English
Similar Records
Planar-nonplanar conformational equilibrium in metal derivates of octaethylporphyrin and meso-nitrooctaethylporhyrin
Metal dependence of the nonplanar distortion of octaalkyltetraphenylporphyrins