Synthesis and characterization of new unsaturated macrobicyclic and bis(macrocyclic) copper(II) complexes containing N–CH2–N linkages

New copper(II) complexes [CuL2]2+ (L2=7,7,9-trimethyl-1,3,6,10,13-pentaazabicyclo[11,2,11.13]hexadec-9-ene) and [Cu2(L3)(H2O)2]4+ have been prepared by the reaction of [CuL1]2+ (L1=5,5,7-trimethyl-1,4,8,11,14-pentaazatetradce-7-ene) and formaldehyde. The mononuclear complex [CuL2]2+ has a square-planar coordination geometry with a 5–6–5–6 chelate ring sequence and is relatively stable even in low pH at room temperature. The dinuclear complex [Cu2(L3)(H2O)2]4+ consists of two unsaturated 15-membered pentaaza macrocyclic units (7,7,9-trimethyl-1,3,6,10,13-pentaazacyclopentadec-9-ene) that are linked together by a methylene group in a tilted face-to-face arrangement [Cu⋯Cu distance: 7.413(2) Å ]. Each macrocyclic unit of [Cu2(L3)(H2O)2]4+ contains one four-membered chelate ring and has a severely distorted octahedral coordination polyhedron. The dinuclear complex is quite stable in aqueous solutions containing an excess of formaldehyde or in dry acetonitrile but is decomposed to [CuL1]2+ and [CuL2]2+ in pure water.