From Chromium–Chromium Quintuple Bonds to Molecular Squares and Porous Coordination Polymers

Reaction of the quintuply bonded chromium­(I) dimer [ApCrCrAp] (Ap = sterically demanding 2-aminopyridinate) with pyrazine yields a chromium­(II) complex with a η⁴:η⁴ face-on coordinated pyrazine dianion. Reaction with 4,4′-bipyridine, on the other hand, completely cleaves the metal–metal bond, leading to a chromium­(II)-based molecular square. XRD and magnetic measurements show ligand radical anions and a ferrimagnetic alignment of alternating metal and ligand magnetic moments. Controlled polymerization of the molecular square with pyrazine yields a porous coordination polymer featuring both reduced and nonreduced linkers.