Structures of Co II and Zn II complexes of the proton‐transfer compound derived from pyrazine‐2,3‐dicarboxylic acid and piperazine

The reaction of the proton‐transfer compound piperazine‐1,4‐diium pyrazine‐2,3‐dicarboxylate 4.5‐hydrate, C 4 H 12 N 2 2+ ·C 6 H 2 N 2 O 4 2− ·4.5H 2 O or (pipzH 2 )(pyzdc)·4.5H 2 O (pyzdcH 2 is pyrazine‐2,3‐dicarboxylic acid and pipz is piperazine), (I), with Zn(NO 3 ) 2 ·6H 2 O and CoCl 2 ·6H 2 O results in the formation of bis(piperazine‐1,4‐diium) bis(μ‐pyrazine‐2,3‐dicarboxylato)‐κ 3 N 1 , O 2 : O 3 ;κ 3 O 3 : N 1 , O 2 ‐bis[aqua(pyrazine‐2,3‐dicarboxylato‐κ 2 N 1 , O 2 )zinc(II)] decahydrate, (C 4 H 12 N 2 ) 2 [Zn 2 (C 6 H 2 N 2 O 4 ) 4 (H 2 O) 2 ]·10H 2 O or (pipzH 2 ) 2 [Zn(pyzdc) 2 (H 2 O)] 2 ·10H 2 O, (II), and catena ‐poly[piperazine‐1,4‐diium [cobalt(II)‐bis(μ‐pyrazine‐2,3‐dicarboxylato)‐κ 3 N 1 , O 2 : O 3 ;κ 3 O 3 : N 1 , O 2 ] hexahydrate], {(C 4 H 12 N 2 )[Co(C 6 H 2 N 2 O 4 ) 2 ]·6H 2 O} n or {(pipzH 2 )[Co(pyzdc) 2 ]·6H 2 O} n , (III), respectively. In (I), pyzdcH 2 is doubly deprotonated on reaction with piperazine as a base. Compound (II) crystallizes as a dimer, whereas compound (III) exists as a one‐dimensional coordination polymer. In (II), two pyzdc 2− groups chelate to each of the two Zn II atoms through a ring N atom and an O atom of the 2‐carboxylate group. In one ligand, the adjacent 3‐carboxylate group bridges to a neighbouring metal atom. A water molecule ligates in the sixth coordination site. The structure of (II) can be described as a commensurate superlattice due to an ordering in the hydrogen‐bonded network. In (III), no water is coordinated to the metal atom and the coordination sphere is comprised of two N , O ‐chelates plus two bridging O atoms. A large number of hydrogen bonds are observed in all three compounds. These interactions, as well as π–π and C=O...π stacking interactions, play important structural roles.