Coordination studies of copper(II), cobalt(II) and iron(II) with isomeric pyridyl-tetrazole ligands

The reaction of 2-(2H-tetrazol-5-yl)pyridine (L1) with 1,6-dibromohexane results in formation of the isomers 2-(6 ''-bromohexyl)-(1-tetrazol-5-yl)pyridine (12) and 2-(6 ''-bromohexyl)-(2-tetrazol-5-yl)pyridine (L3). Coordination reactions of 12 and 13 with CuCl2 center dot 2H(2)O, Co(SCN)(2) and Fe(ClO4)(2)center dot H2O yielded the strongly coloured solids [Cu(II)(L2)Cl-2](2) (1), [Cu(II)(L3)Cl-2](2) (2), [Co(II)(L2)(2)(NCS)(2)] (3), [Co(II)(L3)(2)(NCS)(2)] (4), [Fe(II)(L2)(2)(H2O)(2)](ClO4)(2) (5) and [Fe(II)(L3)(2)(H2O)(2)](ClO4)(2) (6), containing high-spin metal centres for the Co(II) and Fe(II) compounds. X-ray crystal structures were obtained for complexes 1-5. In each complex, ligands L2 and L3 coordinate to the metal centre through the pyridyl N atom and the 1-N site of the tetrazole ring, and the pyridyl-tetrazole ligand remains planar in all cases except 3. Complexes 1 and 2 comprise a central Cu2Cl2 dimeric core with Cu(II) in an essentially square-pyramidal coordination environment. Complexes 3 and 4 contain co(II) in a distorted octahedral coordination environment. In 3, the pyridyl and tetrazole rings of L2 are twisted with respect to each other and the complex adopts a puckered conformation in its equatorial plane. Complex 5 contains water molecules coordinated to Fe(II) in the axial sites, which form hydrogen bonds to the perchlorate counter anions. (C) 2011 Elsevier Ltd. All rights reserved.