Quasi-aromatic Möbius Metal Chelates

Ghodrat Mahmoudi; Farhad A Afkhami; Alfonso Castiñeiras; Isabel García-Santos; Atash Gurbanov; Fedor I Zubkov; Mariusz P Mitoraj; Mercedes Kukułka; Filip Sagan; Dariusz W Szczepanik; Irina A Konyaeva; Damir A Safin

doi:10.1021/acs.inorgchem.8b00064

Quasi-aromatic Möbius Metal Chelates

Inorg Chem. 2018 Apr 16;57(8):4395-4408. doi: 10.1021/acs.inorgchem.8b00064. Epub 2018 Mar 27.

Authors

Affiliations

¹ Department of Chemistry, Faculty of Science , University of Maragheh , 55181-83111 Maragheh , Iran.
² Young Researchers and Elite Club, Tabriz Branch , Islamic Azad University , 51579-44533 Tabriz , Iran.
³ Departamento de Química Inorgánica, Facultad de Farmacia , Universidad de Santiago de Compostela , E-15782 Santiago de Compostela , Spain.
⁴ Department of Chemistry , Baku State University , Z. Xalilov Str. 23 , AZ1148 , Baku , Azerbaijan.
⁵ Centro de Química Estrutural, Instituto Superior Técnico , Universidade de Lisboa , Av. Rovisco Pais , 1049-001 Lisboa , Portugal.
⁶ Organic Chemistry Department, Faculty of Science , Peoples' Friendship University of Russia (RUDN University) , 6 Miklukho-Maklaya Street , Moscow 117198 , Russian Federation.
⁷ Department of Theoretical Chemistry, Faculty of Chemistry , Jagiellonian University , R. Gronostajowa 2 , 30-387 Cracow , Poland.
⁸ Limited Liability Company "NIOST" , Kuzovlevski trakt 2 , 634067 Tomsk , Russian Federation.
⁹ Department of Technology of Organic Substances and Polymer Materials , National Research Tomsk Polytechnic University , 43 Lenin Avenue , 634050 Tomsk , Russian Federation.
¹⁰ Institute of Chemistry , University of Tyumen , Perekopskaya Street 15a , 625003 Tyumen , Russian Federation.

PMID: 29582995
DOI: 10.1021/acs.inorgchem.8b00064

Abstract

We report the design as well as structural and spectroscopic characterizations of two new coordination compounds obtained from Cd(NO₃)₂·4H₂O and polydentate ligands, benzilbis(pyridin-2-yl)methylidenehydrazone (L^I) and benzilbis(acetylpyridin-2-yl)methylidenehydrazone (L^II), in a mixture with two equivalents of NH₄NCS in MeOH, namely [Cd(SCN)(NCS)(L^I)(MeOH)] (1) and [Cd(NCS)₂(L^II)(MeOH)] (2). Both L^I and L^II are bound via two pyridyl-imine units yielding a tetradentate coordination mode giving rise to the 12 π electron chelate ring. It has been determined for the first time (qualitatively and quantitatively), using the EDDB electron population-based method, the HOMA index, and the ETS-NOCV charge and energy decomposition scheme, that the chelate ring containing Cd^II can be classified as a quasi-aromatic Möbius motif. Notably, using the methyl-containing ligand L^II controls the exclusive presence of the NCS^- connected with the Cd^II atom (structure 2), while applying L^I allows us to simultaneously coordinate NCS^- and SCN^- ligands (structure 1). Both systems are stabilized mostly by hydrogen bonding, C-H···π interactions, aromatic π···π stacking, and dihydrogen C-H···H-C bonds. The optical properties have been investigated by diffused reflectance spectroscopy as well as molecular and periodic DFT/TD-DFT calculations. The DFT-based ETS-NOCV analysis as well as periodic calculations led us to conclude that the monomers which constitute the obtained chelates are extremely strongly bonded to each other, and the calculated interaction energies are found to be in the regime of strong covalent connections. Intramolecular van der Waals dispersion forces, due to the large size of L^I and L^II, appeared to significantly stabilize these systems as well as amplify the aromaticity phenomenon.