Abstract
In this contribution we report for the first time fabrication, isolation, structural and theoretical characterization of the quasi-aromatic Möbius complexes [Zn(NCS)2LI] (1), [Zn2(μ1,1-N3)2(LI)2][ZnCl3(MeOH)]2·6MeOH (2) and [Zn(NCS)LII]2[Zn(NCS)4]·MeOH (3), constructed from 1,2-diphenyl-1,2-bis((phenyl(pyridin-2-yl)methylene)hydrazono)ethane (LI) or benzilbis(acetylpyridin-2-yl)methylidenehydrazone (LII), respectively, and ZnCl2 mixed with NH4NCS or NaN3. Structures 1–3 are dictated by both the bulkiness of the organic ligand and the nature of the inorganic counter ion. As evidenced from single crystal X-ray diffraction data species 1 has a neutral discrete heteroleptic mononuclear structure, whereas, complexes 2 and 3 exhibit a salt-like structure. Each structure contains a ZnII atom chelated by one tetradentate twisted ligand LI creating the unusual Möbius type topology. Theoretical investigations based on the EDDB method allowed us to determine that it constitutes the quasi-aromatic Möbius motif where a metal only induces the π-delocalization solely within the ligand part: 2.44|e| in 3, 3.14|e| in 2 and 3.44|e| in 1. It is found, that the degree of quasi-aromatic π-delocalization in the case of zinc species is significantly weaker (by ∼50%) than the corresponding estimations for cadmium systems – it is associated with the Zn–N bonds being more polar than the related Cd–N connections. The ETS-NOCV showed, that the monomers in 1 are bonded primarily through London dispersion forces, whereas long-range electrostatic stabilization is crucial in 2 and 3. A number of non-covalent interactions are additionally identified in the lattices of 1–3.
Highlights
Helical molecules are highly favoured by nature.[1]
The dinuclear ZnII complex fabricated from doubly deprotonated octaethyl formylbiliverdine is the rst established helical doublestranded structure, which was reported in 1976.5 Following this discovery, strategies towards helical structure as well as their self-assembly have been the focus of researchers.[6,7]
The most powerful strategy towards metal-based helical structures is the smart predesign of parent ligands
Summary
Helical molecules are highly favoured by nature.[1]. Such molecules are of great importance, which is supported by the structure of deoxyribonucleic acid rst discovered in 1953.2On the other hand, zinc(II) (ZnII) ions are found in all six main classes of metalloenzymes and are essential for living organisms.[3,4] the dinuclear ZnII complex fabricated from doubly deprotonated octaethyl formylbiliverdine is the rst established helical doublestranded structure, which was reported in 1976.5 Following this discovery, strategies towards helical structure as well as their self-assembly have been the focus of researchers.[6,7] Obviously, the most powerful strategy towards metal-based helical structures is the smart predesign of parent ligands. Complex 1 has a neutral discrete heteroleptic mononuclear structure, where the ZnII metal center is coordinated by one ligand LI via its two pyridyl-imine chelate functions as well as two N-bound NCSÀ anions giving rise to the ZnN6 chromophore with a distorted trigonal-prismatic coordination environment around the cation (Fig. 1, Table S1 in the ESI†), which has been proven by the SHAPE 2.1 so ware.[32,33]
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