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

Copper and zinc complexes of 2,3,5,6-tetra(2-pyridyl)pyrazine (TPPZ) have been prepared. The reaction of Cu(ClO4)2 with TPPZ leads to a dinuclear complex where the ligand is bis-tridentate (crystal data: C24H28N6O22Cl4Cu2, monoclinic, space group P2(1)/n, a = 7.855(4), b = 16.267(6), c = 14.860(3) angstrom, beta = 102.91(3)-degrees, Z = 2, 2522 reflections with I > 2.5sigma(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) angstrom and the Cu...Cl bridging bond is 2.682(2) angstrom. The molecules are stacked up the a axis with a short Cu ... Cu inter-stacking distance of 3.854(4) angstrom. One of the non-coordinated pyridine N atoms is protonated and hydrogen bonded to a perchlorate O atom (crystal data: C24H17N6O8Cl3Cu, triclinic, space group P1BAR, a = 6.873(7), b = 12.753(5), c = 16.252(7) angstrom, angstrom = 69.29(3), beta = 90.10(4), gamma = 83.57(4)-degrees, Z = 2, 3436 reflections with I > 3sigma(I), R = 0.050). The reaction of TPPZ with an excess of ZnCl2 gave a neutral mononuclear five-coordinate complex where TPPZ is mono-tridentate (crystal data: C24H16N6Cl2Zn, monoclinic, space group P2(1)/n, a = 14.744(1), b = 7.245(1), c = 21.253(2) angstrom, beta = 104.51(1)-degrees, Z = 4, 3340 reflections with I > 2.5sigma(I), R = 0.036).