Solvent-driven azide-induced mononuclear discrete versus one-dimensional polymeric aromatic Möbius cadmium(ii) complexes of an N6 tetradentate helical ligand

Abstract

We report the synthesis and structural characterization of a heteroleptic mononuclear discrete complex [Cd(N₃)₂(L)(MeOH)]·MeOH (1·MeOH) and a one-dimensional coordination polymer of the composition [Cd₃(N₃)₆(L)]_n (2), fabricated from Cd(NO₃)₂·4H₂O and the helical organic ligand benzilbis((pyridin-2-yl)methylidenehydrazone) (L) in the presence of two equivalents of NaN₃. The formation of different structures is driven by the solvent. The former complex is formed in the presence of MeOH, while the latter complex is formed in EtOH. The Cd^II centre in 1·MeOH is trapped by the two pyridyl-imine units of the tetradentate ligand L, two azide ligands and one oxygen atom of one methanol ligand with the CdN₆O coordination polyhedron yielding a square face monocapped trigonal prism. The asymmetric unit of 2 consists of three symmetrically independent atoms of Cd^II, six azide anions and one L. The polymeric structure of 2 is realized through chains of the Cd(N₃)₂ units which are decorated with Cd(N₃)₂L units. The Cd^II atoms from the backbone of the coordination polymer have a distorted octahedral coordination, while the remaining Cd^II atom forms a trigonal prism with two basal planes nearly parallel to each other. In both complexes, the 12π electron chelate ring of the CdL fragment is shown to be aromatic by establishing it as a Möbius object. Hirshfeld surface analysis of 1 in 1·MeOH and L in 2 showed that the structures of both species are highly dominated by HX (X = H, C and N) contacts, of which the latter two are highly favoured, as well as some contribution from highly enriched CC contacts is clearly observed.