Solution and Solid State Structure of a Canted, Side-to-Face, Bis(porphyrin) Adduct

Abstract

The coordination chemistry of meso-pyridyl/phenyl porphyrins (PyPs) toward metallo-porphyrins with substitutionally labile axial ligands has been exploited for the self-assembling of ordered arrays of pigments. PyPs are particularly versatile bulding blocks: the peripheral N atom can be either in the 4'-position (4'PyPs) or in the 3'-position (3'PyPs), and they can provide connections to as many as four metal centers by coordination of the pyridyl groups. While 4'PyPs lead to arrays of perpendicularly linked, side-to-face, porphyrins, 3'PyPs yield the corresponding canted analogues. Even though several perpendicular arrays have been described, the examples of canted adducts are few and all very recent. We report here a detailed X-ray structure of the new adduct of two axially ligated canted porphyrins [Ru(TPP)(CO)(3'MPyP)] (1) (TPP = tetraphenylporphyrin, 3'MPyP = 5-(3'-pyridyl)-10,15,20-triphenylporphyrin) as well as its thorough spectroscopic characterization in solution, including the dynamic (1)H NMR investigation of the NH tautomeric exchange process. 1 crystallizes in the monoclinic space group P2(1)/a, Z = 4, with a = 13.508(1) Å, b = 29.972(1) Å, c = 19.084(1) Å, and beta = 96.03(1) degrees. The structural and spectroscopic data of 1 assume a strategic importance among axially ligated pyridylporphyrin systems, since they can be fruitfully compared to those of perpendicular analogues. The importance of a comparative investigation of the canted and perpendicular arrays of porphyrins is readily understood: it might help understanding how relevant physicochemical properties, such as photoinduced long-range electron or energy transfer processes, depend on the mutual orientation of the pigments in the 3-dimensional architecture while the other parameters in the supramolecular array (number of macrocycles, distance between them) are maintained substantially unchanged.

Artificial Molecular Rotors

“…Allesio and co-workers 492 have also investigated an oblique-type PyP: a mono-3-pyridyl porphyrin bound to a Ru(II)-TPP. Again, rotation of the Ru-TPP about the Ru-N bond is fast, as evidenced by the equivalence of the phenyl groups in the NMR, while the individual rotations of the phenyl rings are slow at room temperature.…”

The Pivotal Role of Ru‐dmso Compounds in the Discovery of Well‐Behaved Precursors

“…of the tritopic and trigonal planar linker 2,4,6‐tris‐(4‐pyridyl)triazine (tpt) afforded the molecular trigonal prism [( 73‐Zn ) 3 (µ‐tpt) 2 ] ( 76 ) (Figure ) . The photophysical properties of these, and other, multi‐porphyrin assemblies have been thoroughly studied by the group of Professor Franco Scandola at the University of Ferrara, and the results have been reviewed already …”

Spectroscopic Properties of a Self-Assembled Zinc Porphyrin Tetramer II. Time-Resolved Fluorescence Spectroscopy

“…Many synthetic model systems have been synthesized to obtain a better insight in the energy transfer processes in natural systems. [3][4][5][6][7][8][9][10][11][12] In particular, self-assembled aggregates of metalloporphyrin arrays have been used as building blocks for artificial light harvesting systems and various molecular electronic devices. [13][14][15][16] This work focuses on porphyrin tetramers as models for plant pigments, such as chlorophyll organized in various protein complexes because, similar to these complexes, the tetramers have a fixed, defined structure and show fast energy transfer from a particular excited porphyrin to one or more of its neighbors and loss of excitation energy by relaxation to the ground state [Part I].…”