Single crystals of CoCl2(pyz)2 were prepared for the first time by sol-gel technique using pyrazine in tetramethoxysilane (TMOS) as the gel-forming reagent. The red polymeric Co(II) complex crystallizes in the orthorhombic space group Ccca with lattice parameters a = 10.100(1) Ä, b = 10.672(1) Ä, c = 10.136(1) Ä and Z = 4 formula units, which is in contrast to its former structural description in the tetragonal system. The structure consists of infinite Co(pyz)2 layers parallel (010) with a square planar Co-N4 coordination completed to a nearly undistorted square bipyramide by the two chloro ligands.Einleitung