A new molecular star is born

One thing chemists have learned over the years is that geometry is innate in molecular structures. Besides regular polygons, unexpected shapes often emerge when researchers explore new combinations of metal and ligand components. In one of the latest examples, a team led by Dillip Kumar Chand of Indian Institute of Technology Madras has built a “truncated molecular star,” a pentagram-shaped palladium coordination complex (Chem.–Eur. J. 2017, DOI: 10.1002/chem.201702264). Most self-assembled coordination complexes are built from a metal coordinated with one type of ligand (homoleptic). Complexes made using two or more types of ligand (heteroleptic) are not as common. On top of that, the ligands often are chelating, meaning the ligand binds one metal through two or more atoms. Despite the success in geometrical self-assembling coordination chemistry, Chand and coworkers discovered that their new molecular star is unique not just because of its pointless shape—a pentagon ringed by isosceles trapezoids—but also because it appears to be the first heteroleptic, nonchelating, multicompartment supramolecular coordination complex built with five palladium atoms. The researchers assembled the compound from a palladium(II) salt paired with equal amounts of 1,4-phenylenebis(methyl­ene) diisonicotinate and 4,4′-bipyridine ligands in a one-pot reaction at room temperature. The chemistry behind the cool-looking truncated star molecule isn’t “pointless,” the researchers say, as their study provides new insight on how intricate coordination complex structures form and could lead to guest-binding applications that mimic multicompartmental biological systems.