Chiral or achiral camphorate-based complexes controlled by the conformational rigidity of N-donor co-ligands

Abstract

In this work, based on the chiral source of D-camphoric acid (D-H₂Cam), the effect of configurational rigidity of N-donor co-ligands on the crystallization chiral or achiral metal–organic compounds is explored. Firstly, the somewhat flexible N-donor ligand of 4,4′-bipyridine (4,4′-bpy) in conjunction with chiral D-camphoric acid and Zn(II) ions yields compound 1, Zn₂(D-Cam)₂(4,4′- bpy) (1), which crystallizes in the chiral P2₁ space group and shows the 3D six-connected self-penetrating net so-called LB-1 with the 4⁴6¹⁰8 Schläfli symbol. Afterwards, the replacement of 4,4′-bpy and Zn(II) ions by the relatively less flexible N-donor ligand of 2,2′-bipyridine (2,2′-bpy) and Cu(II) ions produces compound 2, Cu(D-HCam)₂(2,2′-bpy)·H₂O, which crystallizes in the chiral P4₁2₁2 space group and holds the 3D supramolecular (3,6)-connected net labelled as rutile with the (46²)(4²6¹⁰8³) Schläfli symbol. Lastly, the completely rigid N-donor ligand of benzotriazole (BtaH) is used, resulted in compound 3 and 4, namely Zn₃(DL-Cam)₂(Bta)₂ and Co₃(DL-Cam)₂(Bta)₂. Compounds 3 and 4 are isostructural and crystallize in the achiral P space group with the chiral D-camphorate ligand racemized. The structure feature of them is 2D net built on {Zn₃(CO₂)₄ (Bta)₂}_n or {Co₃(CO₂)₄(Bta)₂}_n rod-like building blocks. Moreover, the magnetic studies of 4 disclose a weak antiferromagnetic behaviour that is further interpreted by the non-critical scaling theory.