Synthesis and crystal structure of an M₄L₆ tetrahedral cage with outward-facing pockets from a substituted pyrazolyl–pyridine ligand

The self-assembly of metal–polydentate ligands to give supramolecular tetrahedral complexes is of considerable current interest. A new ligand, 4-benzyl-2-[1-(2-{[3-(4-benzylpyridin-2-yl)-1H-pyrazol-1-yl]methyl}benzyl)-1H-pyrazol-3-yl]pyridine (L), with chelating pyrazolyl–pyridine units substituted on the 4-position of the pyridyl ring with benzyl units, has been synthesized and fully characterized. The self-assembly of L with cobalt(II) gave rise to a tetrahedral cage (hexakis{μ-4-benzyl-2-[1-(2-{[3-(4-benzylpyridin-2-yl)-1H-pyrazol-1-yl]-methyl}benzyl)-1H-pyrazol-3-yl]pyridine}perchloratotetracobalt(II) octakis-(perchlorate) acetonitrile undecasolvate, [Co₄(ClO₄)(C₃₈H₃₂N₆)₆](ClO₄)₇.-11CH₃CN) with approximate T symmetry. The X-ray crystal structure of the cage, i.e. [Co₄L₆⊂ClO₄](ClO₄)₇, shows that the substituted benzyl groups are oriented away from the centres of their respective ligands towards the Co^II vertices, making small outward-facing pockets from three benzyl rings at the corners of the tetrahedron.