INTERACTIONS IN CRYSTALS .112. TETRA(2-PY RIDYL)PYRAZINE - A VERSATILE LIGAND FOR LEWIS-ACIDS - SEMI-ENCAPSULATED AND DOUBLY-ENCAPSULATED COMPLEXES OF COPPER(II) AND NICKEL(II) SALTS

Preceding cyclovoltammetric measurements of tetra(2-pyridyl)pyrazine ( TPP) in aprotic THF solution and the lowering of the reduction potenti al on Li+[B(C6H5)(4)(-)] addition, the crystallization of diprotonated [TPPH2++][B(C6H5)(4)(-)](2) and of ris(2-pyridyl)-1,3,5-triazine(Li+) ][B(C6H5)(4)(-)] have stimulated the preparation and structural charac terization of the following (TPP)(1,2) copper(II) and (TPP)(2) nickel( II) salts: (1) Green TTP-copper(II)-dichloride acetonitrile with Cu2fivefold coordinated by three N contacts to one TPP ligand and by two Cl anions, (2) green di(TPP)-copper(II)-di(perchlorate).2 acetonitrile with fully encapsulated Cu2+ coordinated to six N centers of two TPP ligands, and (3) the analogous nickel(II) complex, brown di(TPP)-nicke l(II)-bis-(tetrafluoroborat).3 water.methanol. Both complexes [(TPP)Me 2+(TPP)](X-)(2) with the Me2+ dications in the cavity provided by two twisted TPP ligands are reported for the first time. The discussion of the crystal structures is based on an extensive search in the Cambrid ge Structural Database, which confirms the distortion mode around the penta-coordinated Cu2+ center, and a more strongly distorted octahedro n at the Cu2+ center relative to that at the six-coordinate Ni2+ cente r as well as shorter contacts Me2+... N to the pyrazine N centers than to the pyridine N centers. The comparison of the monodentate terpyrid yl ligand with the bidentate tetra(2-pyridyl)pyrazine suggests the pre paration of Me+n-bridged polymer chains terminated by terpyridyl compl exation.