Job/Unit: I42546 /KAP1 Date: 17-09-14 19:21:52 Pages: 15 FULL PAPER DOI:10.1002/ejic.201402546 Exploring the Effects of Axial Pseudohalide Ligands on the Photophysical and Cyclic Voltammetry Properties and Molecular Structures of Mg II Tetraphenyl/porphyrin Complexes Khaireddine Ezzayani, [a] Zouhour Denden, [a] Shabir Najmudin, [b] Cecilia Bonifácio, [c] Eric Saint-Aman, [d] Frédérique Loiseau, [d] and Habib Nasri* [a] Keywords: Porphyrins / Magnesium / Ligand effects / Structure elucidation / Pseudohalide ligands The (meso-tetraphenylporphyrinato)magnesium(II) com- plexes with azido (1), cyanato-N (2), and thiocyanato-N (3) ligands were prepared by using 2.2.2-cryptand to solubilize the azide, cyanato, and thiocyanato salts in dichloromethane solvent. These species were characterized by UV/Vis and IR spectroscopy, mass spectrometry, and electrochemistry. The first reduction potential and the two first oxidation potentials of the porphyrin rings of these species are not affected by the nature of the axial ligand, and an unusual third irreversible oxidation of the porphyrin ring is observed. The anodic be- havior of the magnesium azide derivative is complicated by the appearance of additional signals for ligand-centered electron transfers that originate from the release of the azido ligand of 1. The room-temperature fluorescence spectra of the magnesium complexes 1–3 indicate that the Soret and Q bands are not particularly affected by the nature of the axial ligands. The quantum yields of the S 1 S 0 fluorescence are between 0.10 and 0.19, and the fluorescence lifetimes range between 3.7 and 6.1 ns at room temperature. Complexes 1–3 crystallize in the monoclinic crystal system in the same space Introduction The study of magnesium porphyrin species has been of long-standing interest because of their importance in bio- [a] Laboratoire de Physico-chimie des Matériaux, Faculté des Sciences de Monastir, Université de Monastir, Avenue de L’environnement, 5019 Monastir, Tunisia E-mail: hnasri1@gmail.com habib.nasri@fsm.rnu.tn http://www.fsm.rnu.tn [b] Faculdade de Medicina, Veterinària, Universidade de Lisboa, Avenida da Universidade Tecnica, 1300-477 Lisboa, Portugal [c] REQUIMTE/CQFB Departamento de Quimica, Faculdade de Ciencias e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal [d] Département de Chimie Moleculaire, UMR CNRS, Université J. Fourier, 5250, ICMG-FR 2607, Laboratoire de Chimie Inorganique Rédox, 363 Rue de la Chimie, BP 53, 38041 Grenoble Cedex 9, France Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/ejic.201402546 Eur. J. Inorg. Chem. 0000, 0–0 © 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1 group, P2 1 /n. The molecular structure of 1 is the first example of a magnesium azide complex. The average equatorial mag- nesium–N pyrrole bond lengths (Mg–N p ) are higher than those of the related pentacoordinate magnesium porphyrin species and decreases from 1 [2.1187(16) Å] to 2 [2.1108(15) Å] to 3 [2.0962(13) Å]; the distance between the magnesium center and the 24-atom mean plane of the porphyrin ring (Mg–P C ) also decreases from 1 to 2 to 3 with values of 0.6629(7), 0.6598(7), and 0.5797(6) Å, respectively. Complex 1 shows major doming and saddle distortions, whereas 2–3 exhibit relatively high ruffling and moderate doming deformations. The molecular structure of 1 is stabilized by weak inter- molecular C–H···N hydrogen bonds between one carbon atom of the phenyl ring and the terminal nitrogen atom of the azido ligand, and the lattice of 2 exhibits weak inter- molecular C–H···O H bonds between one carbon atom of the phenyl ring and the terminal oxygen atom of the NCO – li- gand. The crystal structure of 3 is mainly sustained by weak intermolecular C–H···C g π interactions between a carbon atom of 2.2.2-cryptand and the centroid of one pyrrole ring. logy. Indeed, the Mg II ion is present as a centrally coordi- nated metal ion in chlorophyll and plays a very important role in photosynthesis. Over the past fifteen years, there has been renewed interest in complexes of magnesium or dia- magnetic metal ions such as Zn II and Cd II with porphyrins owing to their new photoluminescence and closed-shell properties. [1,2] In general, the porphyrin complexes of Mg II are strongly fluorescent, whereas those of open-shell para- magnetic metal ions such as Mn II , Fe II , and Fe III are either nonfluorescent or very weakly fluorescent. Diamagnetic Zn 2+ and Mg 2+ metalloporphyrins display quite similar ab- sorption and emission properties. Zinc(II) porphyrins have been extensively studied, mainly because the insertion of Zn II ions into a porphyrin is very easy compared to the insertion of Mg 2+ ions into the related Mg II –metallopor- phyrins. However, magnesium porphyrins exhibit higher fluorescence quantum yields and longer excited-state life- times compared to those of zinc porphyrins. [3] The magne-