Insights on the UV/Vis, Fluorescence, and Cyclic Voltammetry Properties and the Molecular Structures of Zn II Tetraphenylporphyrin Complexes with Pseudohalide Axial Azido, Cyanato‐ N , Thiocyanato‐ N, and Cyanido Ligands

• Published in: European journal of inorganic chemistry 2015-05, Vol.2015 (15), p.2596-2610
• Main Authors: Denden, Zouhour, Ezzayani, Khaireddine, Saint‐Aman, Eric, Loiseau, Frédérique, Najmudin, Shabir, Bonifácio, Cecilia, Daran, Jean‐Claude, Nasri, Habib
• Format: Article
• Language: English
• Subjects: Chemical Sciences
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.201403214

The syntheses, spectroscopic and photophysical properties, and molecular structures of azido‐ ( 1 ), cyanato‐ N ‐ ( 2 ), thiocyanato‐ N ‐ ( 3 ), and cyanido‐ ( 4 ) ( meso ‐tetraphenylporphyrinato)zinc(II) complexes are reported. These species were prepared by using cryptand‐222 to solubilize the pseudohalide salts in organic solvents. The UV/Vis spectra of these zinc metalloporphyrins are solvent‐dependent and exhibit large redshifted Soret bands compared with those of the [Zn(Porph)L] derivatives in which Porph is a meso ‐porphyrinato ligand and L is a monodentate neutral axial ligand. The room‐temperature fluorescence spectra of the zinc complexes 1 – 4 indicate that the Q bands are not very affected by the nature of the axial ligands, and their positions are very close to those of previously reported ( meso ‐porphyrinato)zinc complexes. The quantum yields of the S 1  → S o fluorescence of 1 – 4 range between 2.8 and 5.5 %, and their fluorescence lifetimes are the same (1.7 ns). Cyclic voltammetry investigations on 1 – 4 show that the characteristic potentials for the reduction and the two first oxidations of the porphyrin ring are not very affected by the nature of the axial ligand. A third irreversible oxidation of the porphyrin ring is observed. Additional anodic irreversible waves are observed for the thiocyanato‐ N ( 3 ) and cyanido ( 4 ) species. The solid‐state molecular structures of 1 – 4 are the first examples of zinc porphyrin complexes with anionic ligands. The average equatorial zinc–pyrrole N atom (Zn–N p ) distances for 1 – 4 range between 2.083(1) and 2.117(2) Å and are much longer than those of the related pentacoordinate zinc porphyrin complexes with monodentate neutral ligands. As a consequence, the displacement of the Zn 2+ cation from the mean 24‐atom plan of the porphyrin core is significant (ca. 0.5 Å), and the porphyrin core is very distorted. The crystal structures of 1 – 4 are stabilized by weak intermolecular π interactions, C–H ··· Cg (Cg are the centroids of some six‐membered phenyl rings and five‐membered pyrrole rings). The molecular structure of 1 is further stabilized by weak intermolecular C–H ··· N hydrogen bonds between one carbon atom of cryptand‐222 and the terminal nitrogen atom of the azido ligand.