Solvent-induced formation of novel ni(Ii) complexes derived from bis-thiosemicarbazone ligand: An insight from experimental and theoretical investigations

In this work, we report solvent-induced complexation properties of a new N2S2 tetradentate bis-thiosemicarbazone ligand (H2LI), prepared by the condensation of 4-phenylthiosemicarbazide with bis-aldehyde, namely 2,2’-(ethane-1,2-diylbis(oxy)dibenzaldehyde, towards nickel(II). Using ethanol as a reaction medium allowed the isolation of a discrete mononuclear homoleptic complex [NiLI ] (1), for which its crystal structure contains three independent molecules, namely 1-I, 1-II, and 1-III, in the asymmetric unit. The doubly deprotonated ligand LI in the structure of 1 is coordinated in a cis-manner through the azomethine nitrogen atoms and the thiocarbonyl sulfur atoms. The coordination geometry around metal centers in all the three crystallographically independent molecules of 1 is best described as the seesaw structure. Interestingly, using methanol as a reaction medium in the same synthesis allowed for the isolation of a discrete mononuclear homoleptic complex [Ni(LII)2 ] (2), where LII is a monodeprotonated ligand 2-(2-(2-(2-(dimethoxymethyl)phenoxy)ethoxy)benzylidene)-N-phenylhydrazine-1-carbothioamide (HLII). The ligand LII was formed in situ from the reaction of LI with methanol upon coordination to the metal center under synthetic conditions. In the structure of 2, two ligands LII are coordinated in a trans-manner through the azomethine nitrogen atom and the thiocarbonyl sulfur atom, also yielding a seesaw coordination geometry around the metal center. The charge and energy decomposition scheme ETS-NOCV allows for the conclusion that both structures are stabilized by a bunch of London dispersion-driven intermolecular interactions, including predominantly N–H···S and N–H···O hydrogen bonds in 1 and 2, respectively; they are further augmented by less typical C–H···X (where X = S, N, O, π), CH···HC, π···π stacking and the most striking, attractive long-range intermolecular C–H···Ni preagostic interactions. The latter are found to be determined by both stabilizing Coulomb forces and an exchange-correlation contribution as revealed by the IQA energy decomposition scheme. Interestingly, the analogous long-range C–H···S interactions are characterized by a repulsive Coulomb contribution and the prevailing attractive exchange-correlation constituent. The electron density of the delocalized bonds (EDDB) method shows that the nickel(II) atom shares only ~0.8|e| due to the σ-conjugation with the adjacent in-plane atoms, demonstrating a very weak σ-metalloaromatic character. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

Mahmoudi G. 1 , Babashkina M.G.2 , Maniukiewicz W.3 , Afkhami F.A.4 , Nunna B.B.5, 6 , Zubkov F.I. 7 , Ptaszek A.L.8 , Szczepanik D.W.8 , Mitoraj M.P.8 , Safin D.A.9, 10, 11
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  • 1 Department of Chemistry, Faculty of Science, University of Maragheh, P.O. Box, Maragheh, 55181-83111, Iran
  • 2 Institute of Condensed Matter and Nanosciences, Université Catholique de Louvain, Place L. Pasteur 1, Louvain-la-Neuve, 1348, Belgium
  • 3 Institute of General and Ecological Chemistry, Lodz University of Technology, Żeromskiego 116, Łódź, 90-924, Poland
  • 4 Department of Chemistry, The University of Alabama, Box 870336, 250 Hackberry Lane, Tuscaloosa, AL 35487, United States
  • 5 Department of Mechanical and Industrial Engineering, New Jersey Institute of Technology, University Heights, Newark, NJ 07102, United States
  • 6 Department of Medicine, Brigham and Women’s Hospital, Division of Engineering in Medicine, Harvard Medical School, Harvard University, Cambridge, MA 02139, United States
  • 7 Organic Chemistry Department, Faculty of Science, Peoples’ Friendship University of Russia (RUDN University), Miklukho-Maklaya Str. 6, Moscow, 117198, Russian Federation
  • 8 Department of Theoretical Chemistry, Faculty of Chemistry, Jagiellonian University, Gronostajowa 2, Cracow, 30-387, Poland
  • 9 Institute of Chemistry, University of Tyumen, Volodarskogo Str. 6, Tyumen, 625003, Russian Federation
  • 10 Innovation Center for Chemical and Pharmaceutical Technologies, Ural Federal University Named after the First President of Russia B.N. Eltsin, Mira Str. 19, Ekaterinburg, 620002, Russian Federation
  • 11 Kurgan State University, Sovetskaya Str. 63/4, Tyumen, 640020, Russian Federation
Ni interactions; σ-metalloaromaticity; Ni(II) complexes; intermolecular C–H
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