We report design and structural characterization of three new coordination compounds fabricated from Cd (NO3)2·4H2O and a helical organic ligand benzilbis((pyridin-2-yl)methylidenehydrazone (L) in the presence of two equivalents of NaHal (Hal=Cl, Br, I) in a mixture of MeOH and EtOH, namely [CdCl2L]·1.5MeOH (1), [CdBr2L]·EtOH (2) and [CdI2L] (3). The synthesis and design strategy involved using a branched tube, where temperature differential led to slow crystallization of the compounds. The ligand L is bound via two pyridylimine units with a tetradentate coordination mode yielding the 12π electron chelate ring. All the structures are stabilized by intermolecular hydrogen bonding and C–H⋯π interactions. Hirshfeld surface analysis showed that the structures of all the complexes are highly dominated by H⋯X (X=H, C and Hal) contacts. The optical properties of 1–3 have been investigated by diffuse reflectance spectroscopy. 1–3 each exhibit bands almost exclusively in the UV region up to about 450 nm, and the band gap energies were estimated to be 2.92, 3.03 and 3.11 eV, respectively.
