Pyrazinetetracarboxamide: A Duplex Ligand for Palladium(II)

Tetraethylpyrazine-2,3,5,6-tetracarboxamide
forms a dipalladium­(II) complex with acetates occupying the fourth
coordination sites of the two bound metal ions. Crystallographic results
indicate that the “duplex” dipincer has captured two
protons that serve as the counterions. The protons lie between adjacent
amide carbonyl groups with very short O···O distances
of 2.435(5) Å. In the free base, the adjacent carbonyl groups
are farther apart, averaging 3.196(3) Å. While the dipalladium­(II)
complexes stack in an ordered stepwise fashion along the a axis, the free base molecules stack on top of each other, with each
pincer rotated by about 60° from the one below.