title: Substituent-Induced Perturbation Symmetries and Distortions of meso-tert-Butylporphyrins.
abstract: The out-of-plane and in-plane distortions of a series of nickel(II) meso-substituted porphyrins with 0, 1, 2, or 4 tert-butyl groups [nickel(II) porphine (NiP), nickel(II) mono-tert-butylporphyrin (NiMtBuP), nickel(II) di-tert-butylporphyrin (NiDtBuP), and nickel(II) tetra-tert-butylporphyrin (NiTtBuP)] are investigated using molecular mechanics (MM) calculations, X-ray crystallography, UV-visible absorption spectroscopy, and resonance Raman spectroscopy. MM calculations are used to predict the stable conformations for this series of porphyrins. The out-of-plane distortions are then analyzed in terms of displacements along the normal coordinates of the porphyrin macrocycle using a new normal-coordinate structural decomposition method. As expected, the distortions are found to occur primarily along the lowest-frequency normal coordinate of each symmetry type and the distortions could be adequately simulated using only the lowest-frequency normal coordinates as a basis (the minimal basis). However, the distortions could be simulated significantly more accurately by extending the minimal basis by including the second-lowest-frequency normal coordinate of all symmetries. Using the extended basis is most important for the in-plane distortions. Detailed analysis of the types of distortion revealed that both the out-of-plane and the in-plane distortions depend on the perturbation symmetry of the peripheral substituents. The symmetry primarily depends on the pattern of substitution (number and positions of substituents) and the orientations of substituents. Often the perturbation symmetry can be predicted for a given porphyrin simply from the possible orientations of the substituents. Then, the main type(s) of symmetric deformation occurring for each possible molecular symmetry can be readily predicted from a D(4)(h)() correlation table. The stable conformers predicted by MM for the series of tert-butyl-substituted porphyrins confirm this simple but informative approach. Experimental verification of the calculated contributions of the symmetric deformations is provided by normal-coordinate structural decomposition of the available X-ray crystal structures of NiP, NiMtBuP, and NiDtBuP. The solid-state results are also supported by the resonance Raman and UV-visible absorption spectroscopic characterization of the porphyrins in solutions. The X-ray crystal structure of NiMtBuP is reported here for the first time.
authors.affiliation: Materials Theory and Computation Department, Sandia National Laboratories, Albuquerque, New Mexico 87185-1349, Department of Chemistry, University of New Mexico, Albuquerque, New Mexico 87131, Klinik und Poliklinik für Nuklearmedizin, Universität GH Essen, Hufelandstrasse 55, D-45147 Essen, Germany, and Department of Chemistry, University of California, Davis, California 95616.
authors.forename: Xing-Zhi
authors.initials: XZ
authors.lastname: Song
authors.forename: Walter
authors.initials: W
authors.lastname: Jentzen
authors.forename: Laurent
authors.initials: L
authors.lastname: Jaquinod
authors.forename: Richard G.
authors.initials: RG
authors.lastname: Khoury
authors.forename: Craig J.
authors.initials: CJ
authors.lastname: Medforth
authors.forename: Song-Ling
authors.initials: SL
authors.lastname: Jia
authors.forename: Jian-Guo
authors.initials: JG
authors.lastname: Ma
authors.forename: Kevin M.
authors.initials: KM
authors.lastname: Smith
authors.forename: John A.
authors.initials: JA
authors.lastname: Shelnutt