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.