Formation of cobalt(II)-piperazine supramolecular systems under different organic acid mediums: synthesis, characterization and crystal structures

The reactions Of CoCl2 salt and piperazine (L) in the presence of different organic acid mediums afford a series of cobalt(II) complexes, the solid structures (determined by X-ray diffraction techniques) of which are controlled by the nature of the specific acid. When terephthalic acid was used, a novel mononuclear molecule [Co(HL)(2)Cl-3].Cl.(H2O) (1) was obtained [orthorhombic, Pnma, a = 24.604(16) Angstrom, h = 9.882(7) Angstrom, c = 6.609(4) Angstrom, Z = 4], in which the Co-II center takes the unusual compressed trigonal-bipyramidal coordination geometry (CoN2Cl3) and multiple hydrogen-bonding interactions extend this structure into a three-dimensional supramolecular network. However, with the replacement of terephthalic acid with malonic acid in the above reaction, a one-dimensional coordination polymer [CoLCl2](n) (2) was obtained [monoclinic, P2(1)/n, a = 6.363(3) Angstrom, b = 10.244(5) Angstrom, c = 12.124(5) Angstrom, beta = 103.560(8)degrees, Z = 4], in which the tetrahedral Co-II centers (CoCl2N2) are linked by the bidentate-coordinated piperazine molecules to form a zigzag chain array and these coordination chains are further expanded to a three-dimensional hydrogen-bonding architecture. In addition, a mononuclear complex [Co(gly)(3)].H2O) (3) [monoclinic, P2(1/)c, a = 6.261(5) Angstrom, b = 14.280(9) Angstrom, c = 12.182(8) Angstrom, beta = 10 1.450(14)degrees, Z = 4] was yielded when glycine was used in the similar procedure. A three-dimensional framework is also observed through the hydrogen-bonding interactions between [Co(gly)(3)] moieties, in which the guest water molecules are included. These results unequivocally indicate that the nature of the organic acid templates play the key role in formation of these complexes. (C) 2004 Elsevier B.V. All rights reserved.