Synthesis and characterization of CrIII, FeIII, CoII, NiII, Cull and ZnII complexes of 2, 14-dimethyl-3, 15-di-n-propyl-1 ,4,13, 16- tetraazacyclotetracosa-1 ,3, 13,15-tetraene - R. N. Prasad (2011)