Nickel(II) complexes of the macrocyclic ligand 5-nitromethyl-5,7,12,14-tetramethyl-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) complex of C-meso-5,7,12,14-tetramethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene gives the nickel(II) complex of the 5-nitromethyl derivative containing a pendant nitro group. The complex is octahedral with the nitro group coordinated to nickel(II) via the aci-nitro tautomer. Although the complex contains one water molecule, six-coordination occurs by interaction with a neighbouring -CH=NO2- group in a polymeric structure. Recrystallisation 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 solution, NiL + 2H(2)O reversible arrow NiL(H2O)(2), with K = 0.28 at 40 degrees C. The thermodynamic, parameters for this equilibrium are Delta 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 spectroscopic results discussed.