Crystal and molecular structures of Cu(II) and Zn(II) complexes of 2,3,5,6-tetra(2-pyridyl)pyrazine (TPPZ): an old ligand revisited

Abstract

Copper and zinc complexes of 2,3,5,6-tetra(2-pyridyl)pyrazine (TPPZ) have been prepared. The reaction of Cu(ClO 4) 2 with TPPZ leads to a dinuclear complex where the ligand is bis-tridentate (crystal data: C 24H 28N 6O 22Cl 4Cu 2, monoclinic, space group P2 1/ n, a=7.855(4), b=16.267(6), c=14.860(3) Å, β=102.91(3)°, Z=2, 2522 reflections with I>2.5σ( I), R=0.053). In an acidic medium the same reaction gave a mononuclear dimeric complex where TPPZ is mono-tridentate. The Cu…Cu separation in the dimer is 3.446(3) Å and the Cu…Cl bridging bond is 2.682(2) Å. The molecules are stacked up the a axis with a short Cu…Cu inter-stacking distance of 3.854(4) Å. One of the non-coordinated pyridine N atoms is protonated and hydrogen bonded to a perchlorate O atom (crystal data: C 24H 17N 6O 8Cl 3Cu, triclinic, space group P 1 , a=6.873(7), b=12.753(5), c= 16.252(7) Å, α=69.29(3), β=90.10(4), γ=83.57(4)°, Z=2, 3436 reflections with I>3σ( I), R=0.050). The reaction of TPPZ with an excess of ZnCl 2 gave a neutral mononuclear five-coordinate complex where TPPZ is mono-tridentate (crystal data: C 24H 16N 6Cl 2Zn, monoclinic, space group P2 1/ n, a=14.744(1), b=7.245(1), c= 21.253(2) Å, β=104.51(1)°, Z=4, 3340 reflections with I>2.5σ( I), R=0.036).