NICKEL(II) COMPLEXES OF THE MACROCYCLIC LIGAND AMETHYL-1,4,8,11-TETRAAZACYCLOTETRADECA-4,11-DIENE CONTAINING A PENDANT NITRO-GROUP

The reaction of MeNO2 in the presence of Et3N with the nickel(II) comp lex of amethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene gives the ni ckel(II) complex of the 5-nitromethyl derivative containing a pendant nitro group. The complex is octahedral with the nitro group coordinate d to nickel(II) via the aci-nitro tautomer. Although the complex conta ins one water molecule, six-coordination occurs by interaction with a neighbouring -CH=NO2- group in a polymeric structure. Recrystallisatio n from aqueous ammonia gives a blue paramagnetic complex with lattice ammonia. Addition of HClO4 to the blue paramagnetic hydrate gives the orange-brown diperchlorate salt with a pendant nitro group. This salt displays a planar reversible arrow octahedral equilibrium in aqueous s olution, NiL + 2H(2)O reversible arrow NiL(H2O)(2), with K = 0.28 at 4 0 degrees C. The thermodynamic, parameters for this equilibrium are De lta H = -59 +/- 2 kJ mol(-1) and Delta S -200 +/- 5 J K-1 mol(-1). The nitro group can be reduced with Zn/HCl to give the amino derivative. The configurations of the complexes are considered and the spectroscop ic results discussed.