Structural versatility of the quasi-aromatic Möbius type zinc(ii)-pseudohalide complexes - experimental and theoretical investigations.

In this contribution we report for the first time fabrication, isolation, structural and theoretical characterization of the quasi-aromatic Möbius complexes [Zn(NCS) 2 L I ] (1), [Zn 2 (μ 1,1 -N 3 ) 2 (L I ) 2 ][ZnCl 3 (MeOH)] 2 ·6MeOH (2) and [Zn(NCS)L II ] 2 [Zn(NCS) 4 ]·MeOH (3), constructed from 1,2-diphenyl-1,2-bis((phenyl(pyridin-2-yl)methylene)hydrazono)ethane (L I ) or benzilbis(acetylpyridin-2-yl)methylidenehydrazone (L II ), respectively, and ZnCl 2 mixed with NH 4 NCS or NaN 3 . 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 Zn II atom chelated by one tetradentate twisted ligand L I 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.