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.