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 octahedral equilibrium in aqueous solution, NiL+2H2O NiL(H2O)2, with K=0.28 at 40degC. The thermodynamic parameters for this equilibrium are DeltaH=-59+2kJmol-1and DeltaS=-200+5JK-1mol-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. This revised version was published online in June 2006 with corrections to the Cover Date.