Synthesis and structures of four homochiral metal camphorates with auxiliary bipyridine ligands

Four homochiral metal camphorates with auxiliary bipyridine ligands are hydrothermally synthesized and structurally characterized. The structure of compound [Cd(d-Hcam)2(bpa)(H2O)]n (1; d-H2cam = d-(+)-camphoric acid, bpa = 1,2-bis(4-pyridyl)-ethane) presents a rare case where the d-Hcam is not a bridging ligand, but a dangling unit attached to the infinite [Cd(bpa)] chain. Compounds [M2(d-cam)2(4,4′-bipy)(H2O)4]n (M = Co, 2; M = Cd, 3; 4,4′-bipy = 4,4′-bipyridine) are isostructural and have homochiral [M(d-cam)]n chains linked by the 4,4′-bipy ligands into a honeycomb-like 63 layer. Compound [Zn2(d-cam)2(PPE)2]n (4, PPE = 1-(4-pyridyl)-2-(2-pyridyl)-ethylene) consists of the grid-like 44 layers with the dinuclear Zn2(COO)4 units and d-cam ligands, where the PPE ligands are only monodentately coordinated to the dinuclear units and act as the separators between two homochiral layers. The results demonstrate the rich coordination chemistry of the enantiopure d-camphorate ligand and the structural diversity of metal–camphorate compounds.